First of all this is with an L98 motor and 91 octane gasoline. According to DynoSim the difference between installing the cam with the intake closing at 65* ABDC and 66*ABDC is 7 horsepower at 5500 rpm in favor of the 66*. However the dynamic compression ratio drops from 8.53:1 to 8.46:1 when retarding the cam just the one degree. I don't know if DynoSim takes this into account when computing the horsepower. Looking for every last bit of horsepower. Any thoughts appreciated.

 

Well this question is no longer relevant to my situation. The Speed-Pro forged pistons I had bought were advertised to have a valve relief of 3.4 cc's and that is what my calculations were based on. I had a couple cc'd today and they came out to 2.8 cc's. Did it twice to make sure.

I will do some minor clean up of the valve relief's, sharp edges and that should make the reliefs around 3.0 cc's. That will put my DCR at 8.50 and static at 10.74. With a quench of .035 that should alow me to run 91 octane gas and my intake valve closing of 66* ABDC. All is well in the world.

 

As I've said DCR is not everything, the right closing point is even if you lose some DCR.... that happens in the real world too.

Bret

 

Thanks Bret. Good point to remember.