Boost modelling questions... [Archive]

Ball Bearing Turbo

9th January 2006, 20:23

I have some questions as to the boost modelling in LFS at the moment... It's been discussed lightly in the past but I couldn't find anywhere that Scawen commented on it at all, save for the ancient days...

After taking a ride in a turbo'd car this weekend (woohoo :razz: ) which actually had a boost gauge installed, I noticed drastically different behaviour in terms of the activity of pressure under certain circumstances.

I realize that systems will differ vastly in their manners depending on numerous factors, but I'm wondering if there are some fundamental things that should be looked at...

First off, since turbochargers are positive feedback devices (more pressure in = more pressure out = more pressure in etc) the gauge indicated that pressure rises faster as it increases, not slower as in LFS. In LFS the needle slows as it approaches max pressure which is the opposite of how it seems things are IRL.:tilt:

Second, I know some cars have more lag than others.... But seriously are some (street, not drag) cars as bad as the cars in LFS? I know it's just one example but the car I rode in this weekend could hit 15lbs at 2200RPM in second gear (it's elecronically limited to 12lbs in first gear).

The LFS RAC: It's almost unbeleivable how much lag that thing has; is that REALLY how that car behaves on the street? :shrug:

I can post video of the gauges during my excursion if anyone needs to see what I am talking about.

Finally, it would be nice to have the vacuum side of the pressure gauge included... I don't think I've seen one anywhere that was just the positive side, correct me if I'm wrong. That would also help to understand what's happening with the boost modelling too.. Hmm maybe that's why it's not there :scratchch

axus

9th January 2006, 20:51

Gunn

9th January 2006, 21:06

I know some cars have more lag than others.... But seriously are some (street, not drag) cars as bad as the cars in LFS?Oh yes. Some experience way more turbo lag. Many modern cars also use a twin turbo system where a smaller turbo helps to maintain boost pressure and therefore reduce lag. But some cars IRL have hideous lag indeed and the advantage of a turbocharger seems absent at all but higher speeds.

Ball Bearing Turbo

9th January 2006, 21:19

The RAC has lag? I have been driving that thing around all day long (even got me a WR) and I can't feel any lag that really affects the way you drive the car. It really depends on the size of the turbo - spool time does not go up linearly as a heavier turbo takes more exhaust gas pressure to turn it the same amount. I'm not sure how it is modelled in LFS but I remember that there was a turbo physics re-write before S2 came out.

RAC HAS LAG????

Egad and gad zooks man, try a standing start - it takes AGES for the needle on the boost gauge to start creeping up... you're ready to shift the instant max pressure is acheived. I'm not talking about losing too much pressure between shifts, but building boost takes eons if there's not already pressure there.... And even when shifting the needle shouldn't lull before it hits max pressure again, that whole "positive feedback" aspect of turbochargers.

As far as the re-write the thread I found on that is seriously ancient and IIRC was pre S1

EeekiE

9th January 2006, 21:23

Supercharging is where it's at for me. I hope one is included at some point, with an adjustable BRV position etc.

Fonnybone

9th January 2006, 21:25

I have some questions as to the boost modelling in LFS at the moment... It's been discussed lightly in the past but I couldn't find anywhere that Scawen commented on it at all, save for the ancient days... :scratchch

Well, i'm not talking in his name at all here, but maybe he just doesn't want to get into arguments about who is right and 'how LFS should be'. I'm sure he appreciates any usefull information, and he reads the forums so don't think he's not paying attention. Also the devs have many things to develop at the same time. Turbo boost might be on their ToDo list, but there might be other stuff above it. That's if it's not already been worked on but simply not released. Also, it's been talked about before as you've mentionned.

Another thing, LFS uses the simulation approach which is contrary to many current games on the market who generally go for the "it
FEELS right" approach which often means simpler code that tries to make you feel like it's right while it's breaking about 10 laws of
physics. So the difference is that the turbo in LFS would need to be reproduced in details instead of using a simple curve to mimic a
turbo's behavior. Same for a supercharger. That might take a little time.

axus

9th January 2006, 21:42

Ball Bearing Turbo

9th January 2006, 21:50

Well, i'm not talking in his name at all here, but maybe he just doesn't want to get into arguments about who is right and 'how LFS should be'. I'm sure he appreciates any usefull information, and he reads the forums so don't think he's not paying attention. Also the devs have many things to develop at the same time. Turbo boost might be on their ToDo list, but there might be other stuff above it. That's if it's not already been worked on but simply not released. Also, it's been talked about before as you've mentionned.

Another thing, LFS uses the simulation approach which is contrary to many current games on the market who generally go for the "it
FEELS right" approach which often means simpler code that tries to make you feel like it's right while it's breaking about 10 laws of
physics. So the difference is that the turbo in LFS would need to be reproduced in details instead of using a simple curve to mimic a
turbo's behavior. Same for a supercharger. That might take a little time.

Indeed... Just to be clear I was in no way trying to appear aggresive, and your post seemed mildly defensive to me so I wanted to make that clear. All I meant by mentioning Scawen was literally what I said, nothing more...

I fully understand and absolutely love the way they are doing this, I've read the forums daily for a couple years now, I'm just starting to try and actually be more active and get involved in the community lately though so... HI!

The passion for truly simulating as many aspects as possible is EXACTLY what drew me to the first releases, and I've always been excited as to where this is going, and that won't change - so please don't take my post as a "complaint" like I've seen on here in the past few weeks, but just a catalyst for some discussion on something that's not brought up very much...

Ball Bearing Turbo

9th January 2006, 21:51

Fonnybone

9th January 2006, 22:48

Indeed... Just to be clear I was in no way trying to appear aggresive, and your post seemed mildly defensive to me so I wanted to make that clear. All I meant by mentioning Scawen was literally what I said, nothing more...

Same here ;) Just making things clear from the start, i don't doubt you enjoy LFS, you ARE here after all ;) I've been around long enough to know how these thread can turn over to the dark side before you can say "i'm your father!" :tilt:

Funnybear

10th January 2006, 00:09

Daddy?

Is that really you?

Hyperactive

10th January 2006, 01:04

No. Im your woorst nitemare!

:D

The turbo in RA is barely noticeable for me. It feels almost NA...

FlintFredstone

10th January 2006, 08:44

It could be down to dump valve settings - the RA has so much torque low down already that in that light a car sudden boost would just spin it. The people that make it could have opted to make the boost get there slower by adjusting the dumpvalve so that the car is actually drivable.

A dump valve has nothing directly to do with boost 'buildup', it is activated when you 'close' the throttle, its purpose is to stop 'overboost' and make sure the turbo does not stall, it does however mean you get a little lag on the next throttle 'open' but atleast the turbo is still spinning to build the boost quickly.

Troy

axus

10th January 2006, 09:54

No, a good turbo allows you to set up the dumpvalve for throttle positions and RPM so you minimaize the effects of turbo lag on drivability. Obviously, you don't actually hear the dump valve when the throttle is open because you want to let out as little boost as possible while having the boost come in smoothly. Once you close the throttle, all boost escapes at once and you hear the dump valve sound.

L(Oo)ney

10th January 2006, 10:05

Daddy?

Is that really you?

PMSL.

I knew there had to be some link between you and fonny.. :D

FlintFredstone

10th January 2006, 10:58

axus

10th January 2006, 11:03

I was always under the impression that it is part of the function of the waste gate/dump valve... trying to do some research on it now but if someone can tell us what it is actually called it will be appreciated. The point is, there is a way to make the turbo work like it does in the RA - spool slowly but smoothly so it doesn't affect drivability that much.

FlintFredstone

10th January 2006, 11:09

The wastegate is the mechanism of diverting the exhaust gasses from the turbo, this is a method used to control spooling/stop overboosting, i know this because my wastegate activator failed leading to overboost leading to the ecu 'panicing' leading to total fuel cut leading to me nearly going through the windscreen :)

Troy

Ball Bearing Turbo

10th January 2006, 15:39

So then....

Am I the only one that thinks there is the possibility of a shortcomming?

Once I get some video editing software installed I will post some video to back up my ramblings...

axus

10th January 2006, 15:46

Ball Bearing Turbo

10th January 2006, 16:10

Ok I can buy the lag argument - but specifically what are your thoughts on the way pressure is built up? I know it's vulgarizing but I mean the "needle slows towards max pressure" rather than the real life behaviour I've witnessed and dug up. If you can tell me with certainty that the phenomenon that happens in LFS happens IRL then it's all cool...

axus

10th January 2006, 16:14

Ball Bearing Turbo

10th January 2006, 16:32

LOL

I guess... Just seems unlikely, people always say "compare LFS to reality" but we can't start bending reality to suit LFS, there a lots of things people "could" do with cars.... But it's not the norm. As stated above wastegates (talking exhaust side) are what mediate boost... And I'm not even certain that the concept you just stated is even possible with them, maybe I am wrong though.

axus

10th January 2006, 16:43

Well look at it this way - with the current, slightly dodgy tyre physics in terms of regaining grip, a snappy turbo would be much harder to control then it would be in real life which is what I imply when I say there are things higher on the list of things to do. So all we are technically doing is using concepts possible in real life to make the cars suit LFS's reality.

Ball Bearing Turbo

10th January 2006, 17:21

I understand.... So your point then is "yes there may be some incongruities happening, but at least we can generates scenarios from reality that could explain the phenomenon"

axus

10th January 2006, 17:24

No, my point is that physics in all aspects has to progress at the same rate because certain bits of the physics rely upon others to be acceptable. Therefore it doesn't make sense to make the turbo physics perfect before the tyre physics because the turbo physics relies on the tyre physics. I think that's fair enough, seing as tyre physics updates are on the way.

Ball Bearing Turbo

10th January 2006, 17:35

I'll buy that, no problem....

And my only point was that perhaps a problem exists, one that people don't talk about very often. That's all...

Huru-aito

10th January 2006, 17:59

What you refer to as the bleeder valve - haven't found the proper name for it - could open more and more as revs build up until maximum boost is reached so that the car isn't as snappy to drive and you get a smooth toque curve. Is that good enough?

Bleeder valves (or bleed valves) are used to cheat the wastegate by bleeding out some of the air going into the wastegate actuator so that the wastegate opens on a bit higher boost levels.

atledreier

10th January 2006, 18:18

Lord_Verminaard

10th January 2006, 19:00

The turbo in RA is barely noticeable for me. It feels almost NA...

Yeah, I get that feeling with nearly every turbo car in LFS. If anyone has played with Netkar, drive the Supra- it has some of the best turbo modeling I have ever seen in a sim. More importantly with the way boost builds and the way the behaviour of the car changes when the boost comes up. I've taken a ride in a street Supra (not anything like the GTR Supra in NetKar) that had an upgraded single turbo, boost maxed at 20 lbs at probably 2600 rpm and held there all the way to redline. Car was pretty fast too. I've also driven many 1.8T VW's (I used to work for VW) some stock, some chipped, and some with upgraded turbos, and the boost responce was nearly the same in all of them, although the upgraded turbo car was a bit more "laggy" down low, it still had nice mid torque but when the turbo came into full song there was that "kick in the back" feeling that hit much harder than the stock turbos did.

I would imagine turbo modeling in a sim would be a very difficult thing to do, especially on cars that are not really based on real-life counterparts with real-world data to compare them to. The exception of the RAC, and from what I have read the engine in that car is nearly identical to the Saab "Viggen" engine which had very quick turbo responce. So who knows.

Brendan

Ball Bearing Turbo

10th January 2006, 19:19

On my engine, a VW 1.8T, the boost buildup is incredibly rapid at low pressures, and gradually ease into it's stable position. I believe this is a function of the ECU, as it controls the wastegate on this engine. This turbo (K3) can easily put out double the boost it's allowed by the ECU, and thus the buildup should be virtually instant. The fact that the K3 turbine is tiny does not affect the overall behaviour of the boost buildup, other than being faster overall. I believe if the ECU left the turbine and wastegate on their own, I'd see the accelerating buildup BBT was expecting.

Having said that, I somehow doupt Scawen has coded in ECU-controlled curves for the wastegate position like VW does. Thus I have no idea why the RAC does this, I only know that it can and does happen in real life.

Interesting. When you say rapid building at low pressures, how low are you talking?

The phenomenon you've transcribed here is still different from the RAC, where the boost gauge needle pretty much moves in unison with the tach... and you need to shift pretty much the instant max pressure (which is quite low on that car) is acheived.. Which is what seems odd to me (talking about roll on from any speed or standing start)

atledreier

10th January 2006, 19:27

With the K3 turbo being so small, I can get full ECU-allowed boost (.55 Bar) from 1400 rpm. If I go WOT at 1800rpm, I have full boost in about 2 seconds, but the boost build pretty fast in the beginning, and slower as I approach full boost. At higher rpm the boost hits full very fast, less than half a second, so it's hard to make out just how the curve is. I'd go film it, but it's dark out so it'd probably just be a blurred mess.

Edit: I've been looking at the turbo behaviour in LFS a little closer and made a few observations. It seems to me turbo spool time is a direct function of throttle position and rpm, and very linear. In real life the low exhaust pressure at low rpm would inhibit any rapid spool, which in turn inhibit a rapid increase in exhaust pressure, making the whole process pretty slow, which is the essence of turbo-lag in the first place.
The other cars seem more natural to me, but they have the power- peak really really high in the rpm band. But then they are race cars, and suppsed to have pointy torque curves.

Ball Bearing Turbo

10th January 2006, 19:29

...boost maxed at 20 lbs at probably 2600 rpm and held there all the way to redline......I would imagine turbo modeling in a sim would be a very difficult thing to do, especially on cars that are not really based on real-life counterparts with real-world data to compare them to. The exception of the RAC, and from what I have read the engine in that car is nearly identical to the Saab "Viggen" engine which had very quick turbo responce. So who knows.

Right, unless it's a drag motor I don't understand this idea of not reaching max boost unless I'm over 4K, wouldn't seem like a drivable street car :shrug:
but again I am no expert which is why I am asking all these questions...

Ball Bearing Turbo

10th January 2006, 19:32

With the K3 turbo being so small, I can get full ECU-allowed boost (.55 Bar) from 1400 rpm. If I go WOT at 1800rpm, I have full boost in about 2 seconds, but the boost build pretty fast in the beginning, and slower as I approach full boost. At higher rpm the boost hits full very fast, less than half a second, so it's hard to make out just how the curve is. I'd go film it, but it's dark out so it'd probably just be a blurred mess.

Edit: I've been looking at the turbo behaviour in LFS a little closer and made a few observations. It seems to me turbo spool time is a function of throttle position and rpm, and very linear.

Cool now the discussion is actually going somewhere....

When it's light out sometime I'd love to see your film!

And good point about the linearity of what happens in LFS, that's exactly what I was getting at in my last post.

Ball Bearing Turbo

11th January 2006, 00:41

In real life the low exhaust pressure at low rpm would inhibit any rapid spool, which in turn inhibit a rapid increase in exhaust pressure, making the whole process pretty slow, which is the essence of turbo-lag in the first place.
The other cars seem more natural to me, but they have the power- peak really really high in the rpm band. But then they are race cars, and suppsed to have pointy torque curves.

Turbochargers are driven more via heat and the pressure differentials created through the restriction on the turbine (exhaust) side. Exhaust pressure in terms of kinetic energy is a tiny fraction of what spools turbochargers up. In essence they run on heat... And when you open the throttle all the way even at low RPM there is magnitudes more heat dumped into the exhaust manifold, which is why they function more the opposite of what you stated and are referred to as "positive feedback devices". As soon as pressure starts to build, serious amounts of heat are generated along with massive cylinder pressures, accounting for the copious amounts of torque generated. More heat causes a faster spool time not a slower one...

The response on the GTR cars I can't comment on, they might just be accurate since they are tiny motors making so much power...I don't know, but the road cars should have much more boost available more evenly through the RPM band.

Sapient

16th January 2006, 21:44

Ball Bearing Turbo

16th January 2006, 22:54

Snaps to Ball Bearing for generating such an informative thread, and to all those replies.:thumb:

I can throw away the rest of the internet now and learn everything I need to know right here:)
I guess we need to keep in mind that LFS is a work in progress......so any deficiencies, whether real or percieved, could simply be a result of unfinished or un-tweaked modelling.
And besides, the RAC is the offspring of Satan, I would rather drive a UF1000 in a 6 hr enduro than spend 10 min in a RAC:)

Thanks!

I think this topic is cool but considering the lack input by many of the local physics gurus (bob? tristan? TODD? skiingman? and others...) perhaps it's only me that finds it fascinating.... Oh well:shrug:

tristancliffe

16th January 2006, 23:40

I'd love to come and chat, but as I don't regularly drive turbo cars, especially ones with a boost gauge, I can't say how it's meant to behave on a general basis, but it sounds as though you do.

I'll keep an eye on this thread, but unless you seriously balls it up, I doubt my limited knowledge will help.

Bob Smith

17th January 2006, 05:40

All I can input is that I tried making the entire smart range with Mechanic (well, with what little we can adjust), and once I had all the engine parameters right, the peak torque and power were spot on for the base model. The rest of the range simply have more boost, and just by altering the boost number to what the cars use in real life, I didn't have to tweak anything else to get power or torque to match up.

So what I'm saying is, while I don't know anything about spool times, the amount of extra torque the turbo creates at a certain boost pressure, seems spot on. :)

atledreier

17th January 2006, 07:09

I drive a turbo car, and I have a boost gauge. Problem is, the turbo is running about idle, as the engine is tax-restricted to hell and back. So my turbine is almost constantly in it's linear range, and not very useful for this discussion. If someone could send me a new ECU, I'd be happy to show you how it behaves... ;)

Ross Burton

17th January 2006, 10:42

FlintFredstone

17th January 2006, 12:17

This is a scooby, may be of use in the descussion

http://media.putfile.com/Scooby60

Troy

Ball Bearing Turbo

17th January 2006, 17:08

So what I'm saying is, while I don't know anything about spool times, the amount of extra torque the turbo creates at a certain boost pressure, seems spot on. :)

I would concur with that, the output at any given boost seems to be accurate, indicating that the "cyber air / fuel" ratio behaves right since power output / fuel consumption are related in LFS...

This part of the boost modelling seems spot on I agree :thumbsup:

Ball Bearing Turbo

17th January 2006, 17:22

Wow it's been a while since I've been on here... enoyed reading the thread. In my experience, a turbo should spool up rather quickly once you're into it's working rev-range. Obviously that is dependant upon the turbo used, and how the ECU is mapped. It's a bit weak, but I have a vid that I used recently when diagnosing where I was losing boost:

http://www.rossburton.com/castlecoombe/Boostleak.MOV

you can only really see the boosguage at the beginning (hard to hold the camera steady and drive at the same time!) but what you'll notice, is that on idle it sits about -0.5, and as soon as I get above about 2200 rpm the boost climbs steadliy. The fact it holds at about .8bar for a few secs is not normal, that was the problem i was trying to fix, but you'll then see it suddenly climb up to 1.5bar (max). This then starts bleeding off at about 5000 rpm to 1bar @ approx. 7000rpm, but I don't see that too often as that'd be breaking the speedlimit even in 2nd :x

If anyone is interested, I'm sure I could get some footage of boost characteristics, but I think the point is seen that once the car is up in the revs, the boost should climb quite rapidly to max boost. In fact, the turbo would continue to build boost until it died were it not for the wastegate frequency valve that electronically limits boost (if it's not ecu controlled, then the tightness of the spring in the wastegate will limit boost).

cheers
Ross

More footage is always better! Thanks for the input and the movie. Another thought following through with your observations: The way the turbochargers behave now in LFS, for any given car, boost would eventually cease to build which also illustrates my point very well. Watching the boost gauge needle ease into position @ max PSI implies that it's limited by "it's own restrictions" (poor wording, gotta be quick @ work I should be coding hehe:schwitz: ) rather than violently trying to build more pressure and suddenly being limited by a wastegate. One could argue that the retardation of the pressure increase near max boost is due to the impeller running out of it's efficiency range, but then boost should start to drop again right away, but it doesn't; it holds for a couple thousand more RPM... That's the other thing we don't see is boost dropping when the engine exceeds peak power output (approach or exceed redline in most cars in LFS). I'm reasonably certain this should happen as well.....

Gotta run back soon got more to say

Ball Bearing Turbo

18th January 2006, 05:27

Note in these vids we can't see people's feet but they still tell a tale to back up my ramblings.

Here is a quick link.... Super high horsepower car so this could compare to how the GTR may act, although this car has more power.... EVO 8, 2L turbocharged motor... putting out 826hp WOW. (No, not Rice Tristan, it's cool really)
http://media.ams-evo8.com/sevo826awhp.wmv

Here's another one.
http://www.oroinvestments.com/turbophile/videos_n_thumbs/gtir/andy_gtir_speedo.avi

Note on this link, most of the way down the page he describes the cars boost characteristics.
http://www.powerlabs.org/jdmsubaru.htm

Here's a race prepped Supra, boost gauge visible in the lower right of his cluster.
http://www.gscdownloads.com/steve/007_2.wmv

Ball Bearing Turbo

20th January 2006, 22:13

If you roll your FX0, and keep your foot on the throttle out of spite and bitterness for having rolled the car, (guess you could test this without the spite and bitterness, it would be healthier), you will notice also that full boost is never acheived, which seems odds since there is no engine damage to impede such shinanigans

Ball Bearing Turbo

13th February 2006, 16:54

*cough*

RevMonkey

15th February 2006, 01:04

coughity cough cough

neRu

15th February 2006, 16:26

It may be a shortcoming what we are trying to say is that the results that LFS produces are believable and explainable and since the RA is the only real life reference point we have, someone who has driven one must say what the turbo lag is like in it. The rest of the cars are non-existent in real life so you can easily use these explainations to say that what LFS does is believable. Therefore, it is not the most important thing on the list.

I know that the engine in a RA is a Saab B204L - the same as in for example a 9-3.
http://video.google.com/videoplay?docid=4050884557241632962&q=saab+9-3

Thats a vid of a quite tuned version, it has alot of spool up time too, but when it's there, it's there.

Being a saab-fanatic, i can tell you, that the RA's base-engine behavior is way of, it needs to build boost quicker, way quicker, but maybe the RA-developers have designed the enginemanagement to disallow fast turboboost, to prevent spinning.

Ball Bearing Turbo

15th February 2006, 17:03

EXCELLENT, a post!

Thanks for the info, that video is insane!

Interesting theory about about the RA design limiting the pressure build rate... Most cars that do this accomplish it via limiting the AMOUNT of boost available, usually in first gear only. So if the RA behaved that way in first gear only, it might be beleiveable but as it is it's silly.

neRu

16th February 2006, 20:02

Might be, that LFS engine modelling not yet allows different turbo-boost-patterns in different gears, and they might just have taken a middle of none boost-restraints, and IRL boost restraint?

Ross Burton

27th February 2006, 12:31

Hey there's been some decent footage posted in this thread since I last check it out!

A few more thoughts:

I've been researching turbo's a bit more and I'm still not sure I understand them all to well, but there's a few things I've been reading about. I'm sure some of this will be novice material to some reading this thread, so to bring it down to my level: :D

First is the efficiency range. A turbo can often put out more boost pressure than is being asked, but this can actually be counter-productive! Adding more pressure is not the answer. For instance, when running my little K24 @ 1.0bar, and then flooring it to 1.5bar, there isn't much increase in power. (Despite the increase in pressure, the turbo is now working at poor efficiency to produce this, therefore heating the air - so, due to the extra heat produced, all it's done is increase pressure and not really increase the airmass!)

Which leads me onto ECU control of the turbocharger - the turbo definitely is limited by the ECU, at least in any newer car. Boost characteristics are quite different for various setups though as they work differently... some are purely mechanical WG's, some entirely ECU controlled WG, others kinda use both. Whilst my turbo settles at 1.5bar, I know of some who've seen the exact same setup settle at 1.8bar. Difference is, that extra 0.3bar is giving very inefficient power (compressor wheel gives optimum efficiency about 1-1.2bar) and spinning the turbo to far higher RPMs than it was designed to - dramatically shortening it's life! It's all down to how the car is mapped, not the natural restrictions of the turbocharger.

The reason the pressure builds to a crescendo that seems quite natural is because the wastegate doesn't suddenly kick in when max boost is achieved, it starts bleeding off right from the start. So even though it's limited, you wouldn't expect it to hit violently.

I think there's so many variables now with different turbo designs, that it'd be more a case of matching which setup could theoretically cause the behaviour seen in a sim, than actually trying to model the behaviour of a specific turbocharger... I think, as long as the model gives an accurate representation of some 'generic features' of any turbocharged engine, it's all good. I haven't raced on LFS:S2 so I probably should to see how it compares... :D

One point, if the turbo won't spool right up when free-revving the engine (ie in neutral or on your roof!) then that's a good sign; you won't see max boost unless the engine is under load IRL. I guess ideally a sim would model a turbo from a compressor map, a virtual ECU map and real-time exhaust temps + flow etc..

Cheers
Ross

Ball Bearing Turbo

27th February 2006, 18:25

One point, if the turbo won't spool right up when free-revving the engine (ie in neutral or on your roof!) then that's a good sign; you won't see max boost unless the engine is under load IRL. I guess ideally a sim would model a turbo from a compressor map, a virtual ECU map and real-time exhaust temps + flow etc..

What you posted is mostly good I think, and provides a good background for this thread... However this last statement requires reproof... Given all the variables that you stated it's not necesarily true. All the required to build boost is heat - which one COULD argue that load helps create I suppose... But load in the engine isn't inherantly required! In fact, I can pull up a video of a car reaching over 10lbs just by revving. That SRT-4 I rode in could almost do this as well.

I'll be back shortly to post that video.

Also, could you clarify what you meant by crescendo in terms of the building up of boost pressure, cause that could go either way (< or >), but only one way is true in my mind.... The biggest point I've been TRYING to make is the fact that boost creates heat which creates more boost which creates more heat etc etc etc, thus there IS a crescendo which increases the speed at which boost builds, the more boost there is the faster it builds! That is exactly WHY we need a wastegate in the first place, boost does not taper itself off!

:thumb:

Ball Bearing Turbo

27th February 2006, 22:55

Here is the afforementioned video.

It speaks for itself!:scratchch

EeekiE

27th February 2006, 22:57

I think the turbo lag is part of the strategy. Just as ABS is banned, it may just be a big lonesome turbo with simple wastegate, due to any form of anti-lag not being allowed. This makes it more competitive as you have to try and keep it on boost as much as possible. Sometimes left foot braking while holding the boost up etc.

It doesn't quite feel right in LFS though. Redlining and engine in neutral would see close to full boost in no time. None of this slow building up like you get on the start line. It also feels too tied in to RPM. Rather than being on a truely independant RPM of it's own.

Anyway, what you want is a supercharger :D

http://www.zen97015.zen.co.uk/BoostGauge.mpg

http://www.zen97015.zen.co.uk/revups.avi Zero lag (Nearly)

Ross Burton

27th February 2006, 22:59

What you posted is mostly good I think, and provides a good background for this thread... However this last statement requires reproof... Given all the variables that you stated it's not necesarily true. All the required to build boost is heat - which one COULD argue that load helps create I suppose... But load in the engine isn't inherantly required! In fact, I can pull up a video of a car reaching over 10lbs just by revving. That SRT-4 I rode in could almost do this as well.

I'll be back shortly to post that video.

Also, could you clarify what you meant by crescendo in terms of the building up of boost pressure, cause that could go either way (< or >), but only one way is true in my mind.... The biggest point I've been TRYING to make is the fact that boost creates heat which creates more boost which creates more heat etc etc etc, thus there IS a crescendo which increases the speed at which boost builds, the more boost there is the faster it builds! That is exactly WHY we need a wastegate in the first place, boost does not taper itself off!

:thumb:

Hi! Yeah, I meant crescendo in terms of building boost not diminishing boost. 100% agree that a wastegate is needed :D

I'm not sure what you mean when you say that all you need is heat to run a turbocharger.... it's the exhaust gases turning the turbine that cause spooling, and this effect is gonna happen regardless of their temperature. Of course, more heat = higher pressure = faster spooling is that's what your getting at. And yes, you're gonna generate alot more heat with all that extra fuel burning in the engine.

As per the car giving boost when free-revving, the SR4 has a diddy little turbo I imagine; of course a small turbo will build more boost free-revving as it takes less to spin it. My K24 isn't exactly large, and it's old-skool (ie, no ball-bearing job) which doesn't help :( . To spool the turbo to max. pressure the engine needs to be under load, or else you simply can't burn enough fuel in it to create enough exhaust gases to spin the turbo fast enough. And you'd really quickly get shedloads of heatsoak if you could...

Cheers
Ross

Ball Bearing Turbo

28th February 2006, 02:27

I'm not sure what you mean when you say that all you need is heat to run a turbocharger.... it's the exhaust gases turning the turbine that cause spooling, and this effect is gonna happen regardless of their temperature. Of course, more heat = higher pressure = faster spooling is that's what your getting at.

:D This is a common misconception. The kinetic energy of the exhaust gases impacting the turbine side is almost negligable compared to the main principle by which turbochargers operate.... It's primarily the expansion of high heat, high pressure gases that drive the turbine. It's not like blowing on my sons shiny air fan thingy that you wave in the wind. Turbine housings are specially engineered to harness the energy of expanding gases. The greater the differential in pressure between the inlet and outlet side of the turbine, the more energy is dumped into the turbine itself. You can spool up a turbocharger bigtime on a bench with a blowtorch, due to the heat.... far more than you can with a hairdryer, even though the hairdryer "moves" more air. This is why with a turbocharged car wants a very large free flowing exhaust system, whereas a NA car benfits most from a properly tuned system, not necessarily a larger diameter system. The larger diameter on the exit side of a turbocharger's turbine makes the pressure differential between the inlet and outlet side larger, and spool times are quicker etc. There is plenty of information available on this topic if you dig, and it's a REALLY common misconception of the the fundamental physics of turbochargers.

As per the car giving boost when free-revving, the SR4 has a diddy little turbo I imagine; of course a small turbo will build more boost free-revving as it takes less to spin it. My K24 isn't exactly large, and it's old-skool (ie, no ball-bearing job) which doesn't help :( . To spool the turbo to max. pressure the engine needs to be under load, or else you simply can't burn enough fuel in it to create enough exhaust gases to spin the turbo fast enough. And you'd really quickly get shedloads of heatsoak if you could...

Did you check the video I posted? hehehe

I do however agree that of couse the dynamics of the system can change dramatically with different turbos / sizes / engines etc, however things just are off in LFS. I can't imagine for the life of me a car behaving like the RA, speaking in terms of the boost delivery... it's unreal, can you imagine trying to pass someone on the highway in that thing? By the time you've got boost you're finished your pass!:shrug:

Ross Burton

28th February 2006, 04:29

:D This is a common misconception. The kinetic energy of the exhaust gases impacting the turbine side is almost negligable compared to the main principle by which turbochargers operate.... It's primarily the expansion of high heat, high pressure gases that drive the turbine. It's not like blowing on my sons shiny air fan thingy that you wave in the wind. Turbine housings are specially engineered to harness the energy of expanding gases. The greater the differential in pressure between the inlet and outlet side of the turbine, the more energy is dumped into the turbine itself. You can spool up a turbocharger bigtime on a bench with a blowtorch, due to the heat.... far more than you can with a hairdryer, even though the hairdryer "moves" more air. This is why with a turbocharged car wants a very large free flowing exhaust system, whereas a NA car benfits most from a properly tuned system, not necessarily a larger diameter system. The larger diameter on the exit side of a turbocharger's turbine makes the pressure differential between the inlet and outlet side larger, and spool times are quicker etc. There is plenty of information available on this topic if you dig, and it's a REALLY common misconception of the the fundamental physics of turbochargers.

Did you check the video I posted? hehehe

I do however agree that of couse the dynamics of the system can change dramatically with different turbos / sizes / engines etc, however things just are off in LFS. I can't imagine for the life of me a car behaving like the RA, speaking in terms of the boost delivery... it's unreal, can you imagine trying to pass someone on the highway in that thing? By the time you've got boost you're finished your pass!:shrug:

Hmm, thanks for the info - expected a reply along those lines :D I wasn't trying to imply it's the kinetic energy in the exhaust gases, but in all honesty I wasn't sure; my understanding is very basic and I understand it to be rather like an aerofoil - it is the difference in pressure that causes the movement; makes sense that this is not just an effect of gases flowing over the compressor wheel like an airplane wing, but caused by a massive pressure increase on the exhaust side due to the mahoosive temps reached. Also explains how the wheel can "stall" (not fun). I almost wish I'd studied fluid mechanics now. :shrug: I can't watch that vid but will post when I can later. Don't seem to have access @ work... without watching, sure the car isnt fitted with an anti-lag system? There is simply no way idle can give large amounts of boost without some assistance or a very small turbo.. just not enough energy avaliable. Could try flooring it and keeping the throttle buried of course, but I doubt the engine would last too long like that! there's a reason dyno's are braked :smileypul

A very informative post though, in fact you've answered a puzzling question to me - I recently had a 3" decatted exhaust fitted with a removed centre box and vent-to-atmosphere WG pipe, it made a HUGE difference to low-end performance and reduced turbo lag. Now it makes complete sense :thumb:

G2G, work to do before the shift ends-

Cheers
Ross

PS any links for reading on this topic much appreciated :D All this turbo-talk gets me excited :pillepall

EeekiE

28th February 2006, 12:21

:D This is a common misconception. The kinetic energy of the exhaust gases impacting the turbine side is almost negligable compared to the main principle by which turbochargers operate.... It's primarily the expansion of high heat, high pressure gases that drive the turbine. It's not like blowing on my sons shiny air fan thingy that you wave in the wind. Turbine housings are specially engineered to harness the energy of expanding gases. The greater the differential in pressure between the inlet and outlet side of the turbine, the more energy is dumped into the turbine itself. You can spool up a turbocharger bigtime on a bench with a blowtorch, due to the heat.... far more than you can with a hairdryer, even though the hairdryer "moves" more air. This is why with a turbocharged car wants a very large free flowing exhaust system, whereas a NA car benfits most from a properly tuned system, not necessarily a larger diameter system. The larger diameter on the exit side of a turbocharger's turbine makes the pressure differential between the inlet and outlet side larger, and spool times are quicker etc. There is plenty of information available on this topic if you dig, and it's a REALLY common misconception of the the fundamental physics of turbochargers.

Did you check the video I posted? hehehe

I do however agree that of couse the dynamics of the system can change dramatically with different turbos / sizes / engines etc, however things just are off in LFS. I can't imagine for the life of me a car behaving like the RA, speaking in terms of the boost delivery... it's unreal, can you imagine trying to pass someone on the highway in that thing? By the time you've got boost you're finished your pass!:shrug:

Makes sense, but why do manufacturers bother with split pulse tubines. Why bother with different A/R ratios if it's only the pressure/heat difference that affects spooling. A turbo spools up quicker when it has distinct pulses of flow, rather than a smooth continuous one. You can reduce turbo lag on a V6 by running two turbos, and sending 3 cylinders worth into each turbo. Even though there would be less heat energy going in. (Assuming the two turbos are just a scaled down version of a bigger alternative that would provide the same boost)

Variable-vane technology would also be useless if it was only down to heat.

ALL of these things drastically affect spool up times.

Heat has an effect because the gas is higher pressure, and this higher pressure will try an equalise past the turbine. Which creates flow. Heat alone wont make it spool. The kinetic flow of the gas is what turns the turbine. Heat of course is what causes the flow. Just as heat expansion is what causes the piston to move down. As the mass of the exhaust is the same as the fuel and air that went in. Nothing extra was created to increase volume.

So on reflection no-one is really wrong, but a turbo is spooled ultimately through kinetic energy, and not thermal. As if you were to seal off the turbine inlet, and put a heat source in it, it wouldn't continue to spin.

Ross Burton

28th February 2006, 14:43

OK had a quick look at the vid. That turbo seems to have minimal lag, and seems like a rather small car, so I'd assume it's a small ball-bearing job that spools very quickly at low rpms (ie, with little flow). And 10psi isn't a huge amount of pressure. I haven't really paid attention yet, but I'm sure my turbo spools to about 5 or so psi on free-revving. Point I'm getting at is that's much less than peak boost, which for me is 22psi.

After some thinking, this is the conclusion I've come to now.. feel free to add comments, rip my comments apart etc or tell me where I'm wrong :tilt:

It's the difference in pressure, that is the primary reason for the turbo to be spooling. The flow has to make a difference, or else porting a turbo or changing A/R ratio's wouldn't make a difference (it quite obviously does). I think it's kinda like holding a vacuum cleaner hose in front of your little desk fan, it starts spinning wildly - the pressure difference on either side of the blades causes them to turn. Of course, in the engine, a bunch of gases at the same temp wouldn't do much. Heat these to 1000degs and there's a huge increase in pressure; of course the faster the turbine spins the quicker pressure is trying to equillise, so you need lots of gases to replace those that are 'escaping' - hence the need for higher revs (and more burnt fuel) to sustain higher boost levels.. you can double the flow without increasing the pressure. it's all inter-related. I'm clueless about pulsing so can't comment, but physics is really wierd so it doen't surprise me!

I don't think it's as much a case of who's correct with what hypothesis, as it is to them all being linked - without the heat, there wouldn't be the extreme pressure difference. This causes the airflow through the turbine which causes it to spin, much like airflow through a prop makes it spin (or like puting a cd on a table and blowing across it makes it lift, just to confuse things :D ). Which is why variable trim turbines are effective; they are angled for optimum spool-up time (ie, by changing the angle they require less flow to turn) and then once spinning change trim level in order to be more effective at higher RPMS. I think Porsche play with that stuff.

Disclaimer - this is just a bunch of my crazy thoughts and I could be entirely wrong.

So, to bring this to LFS relevance - it's all very complex, nobody would ever quite agree so it's best to make a simpler turbo model. However, it does need some improvement as LFS turbo's behave really wierd.

Cheers
Ross

Ball Bearing Turbo

1st March 2006, 22:08

Makes sense, but why do manufacturers bother with split pulse tubines. Why bother with different A/R ratios if it's only the pressure/heat difference that affects spooling.

Whoa, I never said it's the ONLY thing that affects spool times! :x

A turbo spools up quicker when it has distinct pulses of flow, rather than a smooth continuous one. You can reduce turbo lag on a V6 by running two turbos, and sending 3 cylinders worth into each turbo. Even though there would be less heat energy going in.

Twin turbo systems benfit primarily from reduced rotational intertia. You'll have to provide some info about this "pulsing" business, I don't see it making sense. At least I've never heard of what you're describing. More consistent flow produces more consistent work, I can't forsee splitting flow more than necessary creating a positive effect at all :shrug: The amount of heat energy dumped would still be proportional to the size of the turbine, however the mass is less and therefore two small turbochargers react much quicker than one larger one. This is just for twin designs; mating one large and one smaller turbo is a whole different ballgame.

Heat has an effect because the gas is higher pressure, and this higher pressure will try an equalise past the turbine. Which creates flow.

The difference is that the "flow" (read: the dumping of energy into the turbine) happens inside the turbocharger housing, rather than before it. Without high pressure/heat, that cannot happen. I realize that the heat energy is transferred mechanically but it still originates in the form of heat rather than kinetic form. That might be where it ends up, but the fundamental principle is still different from common belief, and this is what I was pointing out. Obviously it takes kinetic energy to apply force to the turbine - but there's a transfer that takes place, hence turbochargers by nature use the wasted thermal energy in exhaust for our benefit. They wouldn't be described as using the velocity of exhaust in the manifold, because that's not really how it works....

So on reflection no-one is really wrong, but a turbo is spooled ultimately through kinetic energy, and not thermal. As if you were to seal off the turbine inlet, and put a heat source in it, it wouldn't continue to spin.

Likewise, without heat, putting airflow through the turbine won't do much either. Therefore thermal energy is a fundamental requirement. Thermal energy is still the "fuel" for the turbine.

edited for clarity

bal00

8th May 2006, 04:44

Interesting thread. We should get the terminology right, though. Boost LAG and the engine speed by which the turbo is producing full boost are two different things.

Boost lag depends on the inertia of the spinning parts...how much is the boost pressure lagging behind compared to a 100% load/constant engine speed scenario. Take the RA up to 220km/h, let off, then floor it at 200km/h. You'll notice it'll take some time to get back up to full boost. That's lag. It's also the reason engines with big turbos often don't reach full boost in the lower gears, even though the engine speed/load would be sufficient.

Boost response on the other hand depends on the geometry of the turbo (turbo vs. engine size, A/R ratio, etc.) and the boost control mechanism and refers to the boost vs. rpm curve you get in a 100% load/costant engine speed scenario barring any lag.

As far as I can tell there are 2 problems with the boost modelling in LFS.
1. Too much lag - After letting off, it simply takes too long to get back full boost.
2. Unrealistic boost response curves - The RA for instance starts making boost at 1000rpm but doesn't reach full boost until 5000 rpm. It should climb steeper and peak sooner. Additionally the boost usually tapers off slightly towards the redline. Manufacturers tend to pick small turbos to improve boost response and low-end torque, and these usually start to choke at high revs.

For reference, here's a small video:
http://www.blinkerfluid.net/0auf290mittel.wmv

The engine is a 2.0L with about 330hp. The turbo is either a KKK K26 or K29, so a good bit bigger than what you would find on the 250hp-ish 2.0L engines in LFS.

A dyno graph along with the boost curve can be found here:
http://www.eds-motorsport.de/Diagramme/Calibra_C20LET_PH-35.jpg
(not the same engine, but an identical one)

The video does a good job of showcasing turbo lag (or lack thereof), boost spike ("overshooting" the target boost level) and the slight drop in boost at higher revs.

Ball Bearing Turbo

8th May 2006, 05:33

THAT, is an awesome video!!! Is that your car?

And it shows everything I've been trying to say this whole thread very very well.

Excellent post, and excellent video. I 100% agree with your post.

:)

330HP from 1 bar on a 2 litre... That's not too shabby either (for a road car)
Noticed the peak at 1.25Bar in 3rd, what are you supposed to be limited at?

bal00

8th May 2006, 22:36

If it was my car, I'd know for sure what kind of turbo is on there. :)
It's supposed to run 1 bar. The spike is due to the manifold being held completely shut for as long as possible. When it actually hits target boost, it takes a bit of time to fully open and bleed off the excess exhaust. This is also why the spike is less pronounced in the upper gears.

Small correction to my post above, which was worded a bit poorly. The actual boost pressure tapering off is more commonly found on modded cars having a stock turbo spinning at the top of its lungs. Completely stock cars usually just see a decrease in efficiency in the upper rev range (hotter air, less density).

Efficiency is also why 1 bar of boost can be either 230hp or 330hp on the same engine, depending on what kind of turbo is used.

Ball Bearing Turbo

9th May 2006, 00:00

If it was my car, I'd know for sure what kind of turbo is on there. :) :doh: I suppose so. Who knows? Maybe you'd been into the sauce :shrug:

It's supposed to run 1 bar. The spike is due to the manifold being held completely shut for as long as possible. When it actually hits target boost, it takes a bit of time to fully open and bleed off the excess exhaust. This is also why the spike is less pronounced in the upper gears.

Small correction to my post above, which was worded a bit poorly. The actual boost pressure tapering off is more commonly found on modded cars having a stock turbo spinning at the top of its lungs. Completely stock cars usually just see a decrease in efficiency in the upper rev range (hotter air, less density).

Efficiency is also why 1 bar of boost can be either 230hp or 330hp on the same engine, depending on what kind of turbo is used.

As you alluded to, the whole purpose of intercooler is greater efficiency at the same boost. Which brings me to a question - when travelling on high mountain roads do turbocharged cars lose power? Assume the same air temperature (although it would be colder most likely, we'll ignore that for now) since the air is less dense at higher altitudes does this affect the output on turbo cars?

If I pressurized a bottle to 14lbs on a high mountain road... And then brought it down to sea level, what would the pressure be in the bottle? I would think that since the external pressure is greater at sea level that the relative pressure in the bottle should drop, therefore an engine running 14lbs on a high mountain road still has less oxygen available to burn than an engine running 14lbs at sea level... correct?

bal00

9th May 2006, 01:40

As you alluded to, the whole purpose of intercooler is greater efficiency at the same boost. Which brings me to a question - when travelling on high mountain roads do turbocharged cars lose power? Assume the same air temperature (although it would be colder most likely, we'll ignore that for now) since the air is less dense at higher altitudes does this affect the output on turbo cars?

Yep, they do, but not as much as naturally aspirated engines. It's easier to understand when you consider the absolute air pressure, not just relative.

Say the atmospheric air pressure at sea level is 14.7 psi absloute. So a naturally aspirated engine has an intake air pressure of...well...14.7 psi absolute. A turbocharged engine at sea level running 1 bar of boost would have a manifold air pressure of 29.4 psi absolute.

At high altitude with an atmospheric pressure of say 12 psi absolute, the naturally aspirated engine would lose ~18.4% of its power cause the air is ~18.4% less dense.
A turbocharged engine would still try to achieve 14.7 psi over atmosphere (remember the wastegate is spring-loaded, and you still need the same amount of boost pressure acting on the spring to compress it), making it 26.7 psi absolute in total, so the turbocharged engine only loses ~9.2% of its power.

Now, what's relevant for the efficiency for the turbo is the pressure ratio across the compressor (boost (abs.)/ambient air pressure (abs.)). While it's 2:1 at sea level, it goes up to 2.225:1 at high altitude. That means depending on the turbos efficiency range, the drop in power may be slightly smaller or slightly bigger than 9.2%. To determine that you'd need the compressor map of the turbo, though.

By the way, modern engines with electronic boost control often have an altitude sensor. At high altitude they pull a small amount of boost in order not to overspin the turbo, despite the higher pressure ratio.

If I pressurized a bottle to 14lbs on a high mountain road... And then brought it down to sea level, what would the pressure be in the bottle? I would think that since the external pressure is greater at sea level that the relative pressure in the bottle should drop,

Well, depends on how you measure it. If said bottle has 14 psi over ambient at 12 psi ambient pressure, it would only have 11.3 psi over ambient at sea level, simply because the reference point changed.

If it has 14 psi absolute at 12 psi ambient, it'll have 14 psi absolute anywhere.

Ball Bearing Turbo

9th May 2006, 02:47

A turbocharged engine would still try to achieve 14.7 psi over atmosphere (remember the wastegate is spring-loaded, and you still need the same amount of boost pressure acting on the spring to compress it), making it 26.7 psi absolute in total, so the turbocharged engine only loses ~9.2% of its power.

Ok, that makes sense. What would the boost gauge read in that situation then - because the wastegate is looking for enough pressure to activate a mechanical gate (which is constant) whereas the gauge will still be reading relative pressure won't it? So then your boost guage may not be giving you accurate info at higher altitudes? Or am I getting confused....

Now, what's relevant for the efficiency for the turbo is the pressure ratio across the compressor (boost (abs.)/ambient air pressure (abs.)). While it's 2:1 at sea level, it goes up to 2.225:1 at high altitude. That means depending on the turbos efficiency range, the drop in power may be slightly smaller or slightly bigger than 9.2%. To determine that you'd need the compressor map of the turbo, though.

That makes perfect sense.

By the way, modern engines with electronic boost control often have an altitude sensor. At high altitude they pull a small amount of boost in order not to overspin the turbo, despite the higher pressure ratio.

If they maintained the same ratio as sealevel then the engine should lose the same % of output as an NA then right?

If it has 14 psi absolute at 12 psi ambient, it'll have 14 psi absolute anywhere.

So, if I capped a bottle at sealevel and took it to space there would be 14.7psi pushing on the inside of that bottle.... Wonder if it would explode; guess that would be the same as pressurizing one to 14.7psi on earth at sea level.

bal00

9th May 2006, 03:37

Ok, that makes sense. What would the boost gauge read in that situation then - because the wastegate is looking for enough pressure to activate a mechanical gate (which is constant) whereas the gauge will still be reading relative pressure won't it? So then your boost guage may not be giving you accurate info at higher altitudes? Or am I getting confused....
Depends on the gauge. An electronic gauge run off the cars MAP sensor will read absolute, since that's all that matters for the ECU. So it would read lower at high altitude.

Most mechanical gauges read relative to ambient, so they'd be accurate.

If they maintained the same ratio as sealevel then the engine should lose the same % of output as an NA then right?
Yep. Most turbos still have some headroom at stock boost levels, though, so the ECU usually allows a slightly higher pressure ratio. As a rule of thumb you need 1% more rpm from the turbo for each 500ft of altitude.

So, if I capped a bottle at sealevel and took it to space there would be 14.7psi pushing on the inside of that bottle.... Wonder if it would explode; guess that would be the same as pressurizing one to 14.7psi on earth at sea level.

Exactly. Btw, if you want something to ponder, what kind of absolute pressure does the air have which a scuba diver breathes at 40m?

Ball Bearing Turbo

18th May 2006, 22:29

I wonder if Scawen has read this thread and what his thoughts are?

Just wondering if boost delivery will be tweaked at all in the future (I'm not asking when... just if...)

Scawen? :)

Viper93

18th May 2006, 23:11

Heya, just read through the thread, when I get back from England I will give a video of me free revving in my SRT-4 then again with a load rolling and then again launching and revving and shifting (effectively a 1/4 mile =P)

(I would do this tonight but someone rear ended the front of my car and it's in the body shop, they tore my bumper, grill and bent my intercooler.... not fun, they drove away too, a new stock intercooler is 600 bucks...)

Ball Bearing Turbo

19th May 2006, 00:47

Heya, just read through the thread, when I get back from England I will give a video of me free revving in my SRT-4

Oh sure, rub it in :nod: LOL

then again with a load rolling and then again launching and revving and shifting (effectively a 1/4 mile =P)

(I would do this tonight but someone rear ended the front of my car and it's in the body shop, they tore my bumper, grill and bent my intercooler.... not fun, they drove away too, a new stock intercooler is 600 bucks...)

Sounds like a good plan thanks for that. Sorry to hear about the "rear ending of the front of your car"... That's a bummer:(

OT: I might be purchasing a certain car with that same mill :D

Viper93

23rd June 2006, 03:03

Ok I am ressurecting this thread, just to give an update... my sticky pod camera mount was sent to the wrong address delaying it for two weeks, I should have it this weekend :banana:

I will show boost in neutral revving, boost in 4th gear from 1800 or so until I deem it becomes not safe anymore(will hit over 120 or so in 4th), and then from a dead stop through 4th gear.

Things to note about SRT-4
Boost is controlled by the stock ECU to keep horsepower constant below like 90-95 degrees air temp depending on how dense the air charge is. During the winter I was running about 4-5 pounds of boost, I should be able to run max boost this time of year though, some days I do some I don't. Anyone feel that this would not model boost properly?

Ball Bearing Turbo

23rd June 2006, 03:07

NO I think it will do wonders

Thank you! Is it also not limited in 1st to 12lbs?

Viper93

23rd June 2006, 03:09

NO I think it will do wonders

Thank you! Is it also not limited in 1st to 12lbs?

Donno it goes by so fast I never had time to look :razz: it's possible, first gear just doesn't last long enough for me to look down there while concentrating on keeping strait, sliding the clutch, and making sure I don't get too much wheel-spin

Shinanigans

23rd June 2006, 07:33

For reference, here's a small video:
http://www.blinkerfluid.net/0auf290mittel.wmv

Nice video.

You can notice in that how just before the car shifts into top gear (5th or 6th? couldnt work out because of the crazy start) that the boost drops off a bit. Then when shifted into top gear, boost actually sits a bit higher then the other gears. :scratchch

My RX7 comes onto boost fairly quickly with the stock turbo, even though i think they're quite large for a stock unit (Hitachi HT-18S). I would be well into the full 10 pounds of boost by the time 2500rpm came along. I haven't even noticed the speed increase of boost from 0-2500rpm though. It just seems to jump up to boost, not a long enough period to notice different speeds.

As the video above shows, boost generally (depending on turbo) comes on 10x quicker then it does in LFS. I would also agree with the point BallBearingTurbo made about them increasing boost faster as they increase boost, which seems to be the opposite in LFS. But as i said above, the time between 0 and full boost for a small to medium sized turbo is a short one, indeed. I also agree with what someone said earlier in regards to the turbo cars feeling like they're N/A. They just seem to lack that punch in the guts.

One of the reasons i was all for engine/parts changing in LFS was because i'd like to fit larger turbos to the cars. I'm a bit of a boost nut and just love the feeling of a truck load of boost building up and getting thrown out the exhaust with the tyres leaving darkies all over the place. Over here i'm labelled as a "rev head" :hyper: lol

I made a quick video of what i think hitting boost should be more like in LFS:

http://files.filefront.com/LFS_Boostwmv/;5179991;;/fileinfo.html

I think the boost noise isn't in sync with the engine RPM/load because as you can see on the 3rd gear launch just after the hairpin coming onto finish straight, it's pretty nicely simulated. But not so nicely simulated coming onto the main straight in 4th previous to this.

This may start evolving into a "this is a racing sim, not NFS boost your car up shite" argument, but please, don't take my post in that direction. That's not what i'm trying to get at. I'm trying to suggest different ways of simulating/recreating boost for LFS, i'm not talking about neons and chrome wiper blades.

For what it's worth, i think the car in that demo had about 300kw + 500nm of torque. Not a rediculous power figure by any means. :thumb:

shim

23rd June 2006, 07:35

just did a 2 second comparison to the XRT and me housemates Skyline R34..

XRT first gear im not even hitting max boost from a stop start with no clutch kicks or anything to get the revs up quicker..

Skyline R34.. boost starts bout 2.5k-3k, and max's out at 4k in first.. (running 8PSI)

the spooling time i believe is too long, sure there is 4PSI difference between the 8PSI (stock) in the skyline and the XRT, but spooling shouldnt take that long..

Blowtus

23rd June 2006, 12:56

My RX7 comes onto boost fairly quickly with the stock turbo, even though i think they're quite large for a stock unit (Hitachi HT-18S). I would be well into the full 10 pounds of boost by the time 2500rpm came along. I haven't even noticed the speed increase of boost from 0-2500rpm though.

you 100% sure on that? when mine was stock it would reach peak boost psi of 6 by about 3000rpm, to reach 10 it takes until about 4000rpm...

Shinanigans

23rd June 2006, 16:12

From memory, yeah. It's been 2 years since i've driven the car though. :scratchch

If i had to give leeway i would say a maximum of 3000 rpm to hit full boost.

Ball Bearing Turbo

23rd June 2006, 19:07

Viper93

23rd June 2006, 19:38

I think consideration has to be given to the fact of how much is required for the CFM requirements of an engine, maybe this is where LFS is off.

An SRT4s 2.4L running roughly the same pressure as the virtual XRT gives almost the same power per displacement, except the SRT4 has a torque peak all the way from 2200-4400RPM (Chris correct me if I'm wrong). None of the turbo'd cars in LFS feel very "torquey" which I think is a bit sad considering they're not 700HP 9000RPM beasts, they're road cars.

You are close about the torque Jeff. Here is a quick dyno http://www.mopar.com/street/products_srt4_stage1.htm. I get at least 250 pounds of torque from 2400-4400. I agree that the road cars in LFS don't have enough torque.

Pls stop knocking SRT's until you have driven one. The engine in them is phenominal, try to find any other engine that produces these kinds of power curves from the factory. It's NOT a neon, trust me, the only cars out there that can beat it in either cornering and accel in the states is the viper and the vette. Even the carrera4S with the tiptronic tranny isn't safe, look at the info for yourself online. 1/4 mile in mid 13's, the ACR will do the skidpad in the low .9's 60-0 110 feet 0-60 in 5.3 seconds. Top this with 30 MPG you cannot beat it. Sure it's FWD, and sure it might look kinda like a neon, but it will kick your ass. We want to use the SRT 2.4 for compairison because that is what the game runs for an engine, with it being turbo'd. We are not talking about a wankel engine that can create tons of revvs, they are totally different engines. Though if I were racing I would almost want one, they just keep making more and more power the higher the revvs and the power curve is relatively flat with the engine being upgraded.

back onto topic:

Shim one reason why the boost came on slow was maybe the ECU was limiting it? Another thing that brings the boost up slow is running low boost pressure, the higher the boost the faster the spool.

Turbocharge

27th June 2006, 02:36

those modded ricer generation supras??...from the vid clips ive seen of them on streetfire.net...the stock turboed ones...seem to accelerate fine...but all the garrett T4 and other style...only hit full boost at almost the redline limiter...would that be the engine not makin enough exhaust until full rpm is reached??

Viper93

3rd July 2006, 23:35

Well I am DLing the editing software so I can stabilize the video, have my camera mount set right, video camera works, now I just need proper lighting :( I think I will wait until tonight to make the video, that way the gauges are easier to see. This week I "should" have this done, sorry for the delay, funding requirements have delayed this project considerably.

Ball Bearing Turbo

4th July 2006, 00:44

Excuses

:razz:

Viper93

12th July 2006, 03:55

Ok here comes for the next barrage of excuses. I updated my bios, forgot to change my setttings in the bios and I spent the remainder of the day trying to remember how to to delete every driver in use and not in use on my friggen system, one good thing came out of this is my computer runs faster again =). Then I had to get my firewire port working, only to find out that the resolution sucks on the camera and I can only capture in 5 second segments... I have to go back to the drawing board and figure out how to get good quality video.

Did a 5th gear up a hill test and noticed that my boost actually starts coming on at 1500, it's linear up to 2300 when I get full boost. I will work on getting a better quality video and see if I can get the software to capture more than 5 seconds at a time with firewire.

Ball Bearing Turbo

15th July 2006, 23:38

Excuses

:razz:

Actually I was thinking of you this week as a navigated the most beautiful area in North America, and maybe more - Beautiful British Columbia, luckily I live only a hour or two from the province so vacationing is easy....

Back on topic, I was pondering how your car would perform on those twisty mountain roads and up the hills. I pondered being able to "Torque" my way up hills with that boost comming on almost for the entire powerband. When you do get the camera going some videos of different conditions like that would be interesting.

If you're travelling in a strait line at say 120k, with your right foot in one position, what happens boostwise if you DON'T move your foot but begin to climb a fairly steep hill? :scratchch

Blowtus

15th July 2006, 23:54

the onset of boost is determined by the amount of air flowing into the engine - the airflow doesn't change if your throttle doesn't change, the speed just drops off ;)
in situations where boost is developing, (more open throttle positions) you'll get more boost (below any sort of max limit) for a given rpm uphill, because it has more time to build.

Ball Bearing Turbo

16th July 2006, 00:55

Yeah I figured nothing would happen, BUT....

I was thinking perhaps some strange thermodynamic things might happen causing the engine to output more heat under that condition or something dumb.... Not really thinking much before posting unfortunately, my brain is fried from driving all day. I was somehow thinking that exhaust temperature would rise under increased load like that but if throttling remains constant nothing should really happen... So... never mind :shrug:

lol

Edit:

Upon some further (albeit minor) contemplation, wouldn't combustion chamber temperatures rise since the same A/F ratio would be used (same throttle position) while the engine decreases RPM due to load? The ignited mixture would remain under higher pressure (& generate more heat) for a longer period before being released into the exhaust manifold (& thus cooled) since there is less time per cycle at lower RPM....

lalathegreat

16th July 2006, 03:16

Upon some further (albeit minor) contemplation, wouldn't combustion chamber temperatures rise since the same A/F ratio would be used (same throttle position) while the engine decreases RPM due to load? The ignited mixture would remain under higher pressure (& generate more heat) for a longer period before being released into the exhaust manifold (& thus cooled) since there is less time per cycle at lower RPM....

No the temperature would not change drastically. This is because of the way the car is tunned. In HighLoad:Low Rpm situations more fuel is injected and Ignition timming is reduced to something like 2 degrees before top dead center.