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 ) 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.

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?

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

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.

Quote from Ball Bearing Turbo :

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.

Quote from axus :

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

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

Quote from Ball Bearing Turbo :

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...

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.

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.

Quote from Fonnybone :

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...

Quote from axus :

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.

True

It already lights 'em up as it is

Quote from Ball Bearing Turbo :

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!"

Daddy?

Is that really you?

No. Im your woorst nitemare!



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

Quote from axus :

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

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.

Quote from Funnybear :

Daddy?

Is that really you?

PMSL.

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

Quote from axus :

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.

Is that not called a 'bleed valve' though?

I could be mistaken

Troy

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.

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

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...

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.

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...

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?

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.

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.

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"