Ok, yes, I know turbocharging has been covered. This is intended to be a very game engine friendly suggestion for the turbo revamp. I have no idea how far along the revamp may be, but I have been doing a lot of reading on turbos recently, and though I would share. I did do a forum search, and didn’t find much in the way of technical descriptions.
As of now we have basic non variable, single geometry turbo chargers. Frankly, these work great, and well represent how those work. Can we split hairs on wheel trim? Sure, but why?
The biggest, and simplest change is based on how this system works now. The system is based on a one turbo per bank model. Splitting this (0, 1, or 2 per bank), coupled with being able to size the turbos independently would be useful. Say you have a V8, and you run 2 per bank (4 turbos) you have 1 pair at one size, and one pair at the other. For an L6 with 2 per bank, you have 2 total, one of each size. This makes an expensive, rudimentary system system so one spins up fast, and the other flows enough for high (engine) speeds. The graph would need 2 colors, one map line for each set.
Pro:
Larger turbo effect area
Quieter exhause
Cons:
Expensive
Slight dip in reliability
Difficult inter-cooler sizing
Edit:
@Watermelon3878 raised a good point about the twin scroll turbocharger. In short, twin scroll is the “tuned exhaust” of turbochargers. The firing pulses are divided evenly into 2 identical exhaust chambers, and so exhaust flow into the turbine is smoothed. I can’t find a good source for when they were introduced, so lets say 10 years later for game purposes. I did find some dyno charts, and a twin scroll is 5-20% better than a single across the power band, much like going from sleeve bearing to ball bearing today. We will just assume the turbo is a twin scroll unless you are running a V6, or V10 with a 1 per bank setup.
This should be simple to add as well, change the calculations for a 5-20-5 bell curve improvement if CYL/2=(whole number) 10 years after turbo tech is available.
Now for the more exotic (or more accurately modern) systems. I don’t know what came first chronologically, so I will explain in the order I studied them. Fortunately they are very similar in concept, and interface.
Variable Geometry Turbocharger (VGT)
A VGT has a set of vanes on the turbine (exhaust side) that make this size change between 2 diamaters during operation.
I am not hinting at diesels, this is just the best picture I found.
Back to it, the interface would work the same way as VVL works in engines right now. Selecting a VGT turbo would give you a second exhaust diameter slider, just like VVL has now.
Pro:
Broader peak boost area
Faster spool without sacrificing flow
Cheaper than doubling up turbos
Cons:
Reliability hit due to hot moving parts
Louder exhaust than a single geometry turbo
Similar to a VGT, there is something called “dual volute” where there are actually 2 separate turbine feeds.
This would also work like the VGT, except the slider would be for the A/R ratio instead of the wheel diameter.
Pro:
More reliable than VGT
Same muffling effect as the single geometry
Con:
Less boost range than VGT
More prone to turbo surge (boost loss on rapid throttle change)
It would not be possible to combine them (yes, I know you can have a VGT in a double volute) so the multiple turbos are for older cars. Expensive, but effective, while the VGT vs. volute would require engine matching. The VGT would favor wide RPM bands, while the volute would be better for long stroke, low speed engines. Plus the similar volute design is more reliable that the VGTs moving parts.
What about turbo materials like aluminum, titanium, ceramic? Quality slider. Sure, I could get stupid overboard (probably have) but the KISS theory or engineering exists for a reason.
Just my $0.02
Superchargers are another animal.