Quote:
Originally Posted by Top-Secret
my buddy and me have been talking about forced air with the compression on the frs/brz with it being 12.5:1 that is already very high as it is. adding 10lbs of boost you ''should'' be around 21:1 and 20lbs of boost ''should'' be around 29.51:1
|
While your concern about cylinder pressure is on the right track, the static compression ratio of 12.5:1 does not tell you how much pre-combustion cylinder pressure you actually end up with. On any engine, due to valve timing, the dynamic compression ratio is lower. Sometimes much lower. On top of that you have the pressure wave effect of intake and exhaust plumbing which affects how much air ends up in the cylinder.
The issue of high pre-combustion pressures is that the air/fuel mixture can heat up to the point of spontaneous ignition (detonation). One of the benefits of direct injection engines is that they can run much higher cylinder pressures due to the cooling effect of injecting fuel during the compression stroke, especially using fuels like e85.