Not sure what formula you’ve used since the update but it’s the first time I’ve played around with it and the exhaust systems seem way too restrictive, you need a 3-3.25" diameter exhaust with tubular headers in the game to match what I know a mere 2.5" diameter exhaust would support in real life (approx 250-260bhp before it becomes much of an issue) Just my 2p, I find the exhaust limiting many OEM builds I’m trying to replicate.
Hmmm, that’s odd, I seem to recall we used some fairly legit data regarding how many L/min a straight pipe could flow and how much air the engine wants to flow.
Maybe the actual flow restriction implementation at the limits aren’t gradual enough?
To make an S2000 motor get the right power for example, it needs to be on a 3" exhaust with long tube headers even with the sliders right up at the highest quality. Put it at the OEM short tube headers with the stock exhaust (which is just over 2.25" diameter), and it looses a lot of horsepower (about 30bhp) If I build a few of the race motors from the buggies, they pretty much all, without fail, need an exhaust 0.75 to 1.00 inch larger than they actually had to get close to the right power output.
Seems a lot more prevailent on high RPM motors, although possibly because they’re the most likely to be running high power on smaller systems.
What data were you using for the pipe flow? Static tests rather than dynamic perhaps?
I’m not a mechanic however an engine that makes 300 horsepower at 3000 rpm requires a larger pipe than another motor that always 300cv but at 7000 rpm. because the fumes of the first are slower.
Maybe is not based on the horsepower but the torque. A 1" pipe can withstand XX NM, the horsepower the engine produces is irrelevant.
Err, no, horsepower = flow.
Also I noticed quite often switching to throttle bodies/race inlet looses a lot of midrange torque/power - shouldn’t happen with correct inlet tract lengths, if anything it should gain.
Hmm. That is odd.
I’d say the thing regarding throttle bodies is.maybe it moving resonant tuning effects up higher rpm?
yes the exhaust diameters seem to be larger than real life for the same power (a 2.5 inch exhaust can hold 350 hp with ease) , but it’s of no consequence in my opinion. it does not affect the game that much (i always look at the max power figure)
regarding the inlets : a short ram intake will allow breathing at higher rpm at the cost of complexity and lowdown torque. this is beacuse air is drawn directly from the throttle plate instead of a plenum that will allow the air to pick up momentum.
The s2000 does have a 55 mm (2.2 inch) exhaust, but it has very long headers, not the short tubes of ordinary cars.
[quote=“Daffyflyer”]Hmm. That is odd.
I’d say the thing regarding throttle bodies is.maybe it moving resonant tuning effects up higher rpm?[/quote]
It could well be, but usually on a race motor you’ll do what you do with the race headers, make them longer to bring an extra harmonic into play, so long as you have room - you can sort of fudge it by switching to throttle bodies and dropping the cam by 6-7, which gives a much more realistic effect imo.
Dark, I have an S2000 engine right in front of me, that why I was modelling one. It has short primaries, and short secondaries. They were deliberately kept short to keep the catalyst temperatures high:
http://i.ebayimg.com/t/00-09-Honda-S2000-OEM-exhaust-manifold-header-F20C-AP1-engine-motor-F20-IVTEC-/00/$(KGrHqYOKnUE3ZRCu-79BN5uPh83bg~~_12.JPG
This is a LONG tube race header for an S2k:
That’s just the primaries!
Holy shit that race header is a work of art…
But that’s a VVL setup, isn’t it?
[quote=“PhillipM”]
[quote=“Daffyflyer”]Hmm. That is odd.
I’d say the thing regarding throttle bodies is.maybe it moving resonant tuning effects up higher rpm?[/quote]
It could well be, but usually on a race motor you’ll do what you do with the race headers, make them longer to bring an extra harmonic into play, so long as you have room - you can sort of fudge it by switching to throttle bodies and dropping the cam by 6-7, which gives a much more realistic effect imo.
Dark, I have an S2000 engine right in front of me, that why I was modelling one. It has short primaries, and short secondaries. They were deliberately kept short to keep the catalyst temperatures high:
This is a LONG tube race header for an S2k:
That’s just the primaries![/quote]
mother of god
that’s a HUGE manifold. seems larger than the engine. 
that thing could hold 600 hp.
well the stock exhaust is as short as they could make it, but it’s still longer than 95 % of the cars i’ve seen, even those that are modded.
The ITB as well as enlarging the intake and exhaust ports or larger exhaust work best with more aggressive cams. the vvl setting of the f20c is already very aggressive so an ITB will allow great breathing in the top range, but impair normal driving.
Yes, it is. On both.
The exact same pattern happens when I model all the PSA TU/XU and EW engines vs throttle bodied versions, vauxhall XE engines, duratecs, old triumphs…I’ve never seen a correctly setup ITB setup loose midrange torque/power.
No, it doesn’t, that’s my point. ITB’s generally reduce the effects of having large cams because the throttle plates are almost shut at low rpms and loads and so prevent the usual charge robbing and pressure fluctuations in the plenum compared to a plenum setup with a throttle body on the end.
As for the manifold lengths, that’s probably because most of the cars you have seen are running a short length header design for space and/or cost reasons, even the modded ones. Automation specifically has long tube and long race designs in there. Which is what the one I posted is.
Anyway, the devs are aware and I imagine a dartboard with my face on it is being erected in the office as we speak.
I did some studying on the internet and through some books i have and it seems ITBs are better at all rpms, but only for engines designed to use them. putting them on a stock engine will mess up the power band. using ITBs with a chamber in front of them will make the best of both worlds. BTW E36 and E46 M3s use ITBs with a chamber in front of them. the R34 GT-r uses them as well to mantain idle smootheness with the long duration cams. many ITB systems also have a rail for equalizing intake pressuse.
That race headers you have cannot easily fit in an S2000. it seems from the picture it was mountes on something else. am i right?
It does fit on something else yes. But you’d find most race cars where the headers aren’t restricted are far longer than the OEM ones. To the point where the cat converter is removed just in order to get the right length in.
That picture on the previous page is ITB’s on a stock engine. You design the ITB’s to suit the engine, not the other way around 
no, no , I meant an engine designed to use ITBs , not around the ITBs. different sensors, different ports, etc.
What different sensors and ports? You don’t need anything any different from the normal engine. It’s just a manifold at the end of the day, that happens to have some throttles in it.
Anyway, it’s not game breaking, just a niggle.
The exhaust potentially is though as high power cars are going to require absolutely massive exhausts to be fitted into the car body somewhere later on in the development. It’ll also stop people replicating stock cars.