How to get more lift out of your stock heads

[Pyro]

Sure the cylinder head flow should be considered in any cam selection. Along with vehicle weight, gear, exhaust flow, engine size, compression, ect. But, I talking in "general". Turbo cams typically have shorter exhaust durations than intake duration which is opposite of a super charger cam.

 

I'm not making it up.

 

He is a little copy and paste from racer brown on turbo cams.

 

Remember: A turbocharger works best as a function of the temperature and velocity of the exhaust gases, and the volume of exhaust gases is secondary. This strongly suggests late exhaust valve opening and early exhaust valve closing so that exhaust gases, in their purest form, can work on the turbo impeller, which is directly connected by the same shaft to the compressor impeller. This doesn't indicate that a turbocharged engine won't function with stock camshafts or those with a relatively long effective exhaust valve durations. It will. But longer exhaust valve durations have drastic effects on the average exhaust gas velocity and temperature. In addition, longer valve overlap periods permit fuel from the pressurised induction system to be pumped out the still-open exhaust valve, lowering exhaust gas temperature and density even further.

This is the primary reason why most stock-but-turbocharged engines feel like you've stepped on a wet sponge at low engine speeds; they're just plain soggy until there is enough of a blast of exhaust gases to wake up the turbo impeller which, in turn, wakes up the compressor impeller.

[pparaska]

Pyro, that all sounds good to me. I'm thinking about playing with the phasing of the cams in my 91 Glalant VR-4 for jsut this reason - lazy low end.