I could be wrong, but this is one factor that makes sense to me.





When you compress air, it heats up.



When you compress air with a turbo, you can cool it with an intercooler (or whatever else), yet still keep it pressurized.



When you compress air in the engine, there's no way to cool it down before the mixture is ignited.



So, it's easier to get a lot more pressure from a turbo and cool it while still keeping pressure, than it is to raise the compression ratio of the motor and keep things from going bang too early.

 

yeah baldy is right, lower compression gives you more room to avoid detonation, and while you do loose a bit, the turbo more than makes up for it.



the FD runs about 125hp a rotor @9.0:1



the na fc runs 80hp per rotor @9.7, which is almost as high as practical



so imma say its got to do with intake heat/vs volumetric efficency



the one that doesnt fit is the 787b, 175hp per rotor on a 10:1 rotor...

 

"the one that doesnt fit is the 787b, 175hp per rotor on a 10:1 rotor..."



Peripheral Port Motors Increase efficiency on the motor bye allowing more volume into the individual rotor.

 

Plus the 787b is being run on race gas which is well over 100-octane so you can up the compression ratio and still not get much in the way of knock.