G-Body_Vet said:
What heads are you using? Was the block decked at all? Not trying to knock your math, but was gasket thickness, piston height and whether you have reliefs/flat/domed pistons taken into account too?
The math was done for me
http://www.kb-silvolite.com/calc.php heads are vortec 64cc, block was not decked, gasket thickness is .035, piston head volume 5 cc
larryo454 said:
I don't think you have over cam the engine but this is my 2cents worth, In my engine static compression is 12.9:1 and run it on the street with a cam that @ .050 int 270 and ext 270 but my engine is a combo.
Its not the static compression I was wondering about it was the dynamic.Larry what degree ABDC does your intakes close?
excerpt from
http://www.empirenet.com/pkelley2/DynamicCR.html
:Why it matters: A 355 engine with a 9:1 static CR using a 252 cam (110 LSA, 106 ICL) has an intake closing point of 52º ABDC and produces a running CR (DCR) of 7.93. The same 9:1 355 engine with a 292 cam (having an intake closing point of 72º ABDC) has a DCR of 6.87, over a full ratio lower. It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane. The larger cam's DCR falls outside this range. It would have markedly less torque at lower RPM primarily due to low cylinder pressures, and a substantial amount of reversion back into the intake track. Higher RPM power would be down also since the engine would not be able to fully utilize the extra A/F mixture provided by the ramming effect of the late intake closing. To bring the 292 cam's DCR up to the 7.5 to 8.5:1 desirable for a street engine, the static CR needs to be raised to around 10:1 to 11.25:1. Race engines, using high octane race gas, can tolerate higher DCR's with 8.8:1 to 9:1 a good DCR to shoot for. The static CR needed to reach 9:1 DCR, for the 292 cam mentioned above, is around 12:1.
This lowering of the compression ratio, due to the late closing of the intake valve, is the primary reason cam manufactures specify a higher static compression ratio for their larger cams: to get the running or dynamic CR into the proper range.
All that I have been reading this evening points out the need for high octane fuel in a "race" engine if yor DCR is 9 or better
