HomemadeTurbo - DIY Turbo Forum

Quote:

Originally Posted by Zeusfire69

I guess I don't get it then...arn't you moving less air/exhaust when you lower comrpession?
Well, the more I think about it, the more it makes sense. You really aren't moving that much less unless you went from like 12:1 to 7:1.

CR has to match camshaft. Your efficiency (at filling the chamber) goes up as CR goes up, but only in the sweet spot of the cam's powerband.

For a stock camshaft, as CR goes up you lose out on low end power because the piston is making that much more suction on the intake stroke against a closed intake valve. When you put the beefy longer duration cam in, it moves the efficient powerband up in the rpm range. Basically, high CR loses efficiency at low RPM operation regardless what you do.

Well, that's the theory, anyway. If you look at some dynos of an engine's power (naturally asphixiated, of course) at the point of spool and 1000-1500 rpm previous, you don't find a huge change for a given engine if manipulating CR, cam, etc. In practice, you only get improvements in spool from displacement. I'm sure one of the much-bukkake'd Big Name engine builders could pull a few tricks, but neither you nor I are they.