Supercharger simulation in BeamNG

This is something that I wouldn't have picked up on before I started playing Forza, and I may be way off-base here, but: the superchargers on cars like the Barstow are obviously modeled as roots/twin-screw (more likely roots) superchargers, but they build boost like centrifugal superchargers, i.e. more RPM = more boost. This may also have something to do with the odd behavior of supercharged engines which may be observed in the torquecurve app, whereby setting a higher rev limiter actually gives more power and torque across the rev range - thus, if the chassis can handle the extra power, it's actually beneficial to set the rev limiter as high as possible with a supercharged car rather than to set it reasonably.

Is there some game-engine limitation which requires this to be the case?

 

Don't all engines in BeamNG do that, though?

 

Well... superchargers of any type are directly driven off the engine, so naturally, the higher the RPM's your at, the faster the supercharger is running, and the more air it will move because of this... and because of this, you end up making more Torque/HP the faster you spin it.

The only reason that supercharged engines start to drop off higher in the RPM range is because they start to lose efficiency the faster you spin them... and seeing as most superchargers spin 2.5 to 3 times the speed of the engine (really depends on the engine/charger, but this is just an average for a roots), they really start to spin faster then they can even draw air in, so up toward the top end, you start to lose boost as the charger just can't keep up with the air that the engine demands.

Pro chargers usually don't have this issue, so they are normally used on higher revving engines, while roots are more common on low revving engines. Roots are for stupid torque down low and mid, Pro are for stupid torque mid and up top as pro chargers can normally keep up with the air flow at higher RPM's.

So by setting the rev limiter higher, you will be spinning everything faster, which assuming the particular charger is efficient enough, should mean that you make more boost, and thus more power (assuming your torque is still going up at that RPM range). This will only give you more power "past" the original rev limit however (again, assuming the torque can keep climbing past the original rev limit)

The way you are wording it, you are making it sound like you are making more power at every RPM rather than just the RPM's that you added above the rev limit. That should not be the case. Power and Torque should stay the same at 3000RPM (or any other) no matter where the rev limit is set... so if this is not the case, then this will garner looking into.

 

I tested it and raising the rev limiter does seem to give more power *at a given RPM*. If you set a supercharged car's rev limiter to 7000RPM, it could quite easily lead to making more power at 5000RPM than it would if you set the rev limiter to, say, 5500RPM. It also seems to lead to peak power and torque being made at a slightly higher RPM, though this is less certain. It's as if the supercharger's boost curve/behavior varies based on how the rev limiter is set.

For the rest, I was assuming that the behavior of twin-screw superchargers in Forza, i.e. making the same boost regardless of RPM (if a given twin-screw blower has 11psi max boost, then it is giving you 11psi whenever you are WOT, from idle all the way to limiter), was the realistic way to simulate them, and that building boost in proportion to RPM was an (undesirable) quirk of centrifugal superchargers.