@rene4406 posted:I have a static ratio of 10.6/1 and an effective ratio of 7.7/1.
I thought that the reduction in the risk of knocking with a more radical camshaft came from the fact that the intake valve closes later, the compression starts later and the pressure at the end of compression and therefore the gas temperature are lower.
I am not the cam design expert.
I do know that what has to happen is that the cylinder pressure under compression needs to be lowered to below the point at which fuel will explode by just being compressed.
In my old school thinking, this is by bleeding off the pressure by leaving the exhaust valve open longer?
If that can be done in other ways, that's fine. If you open the intake later or leave the exhaust open longer that is just the method of achieving the desired effect by the designer.
That is all just done in a computer program these days.
As far as I can determine, the two cams that you are using, the old GP design and the slightly modified new one, are doing that.
The cam grinder should be able to tell you what ignition advance you can use and what fuel octane you need to run on.
In some cases the actual angle of the valves at .500 lift effect the calculation in that the angle it is canted too un-shrouds the valve from the cylinder wall. That is partially why aftermarket heads make more power then their original counterparts did. They change the angle and center to center location of the valve guides in the inline designs but not as much as the canted valve Cleveland head does.
This is why canted valve Cleveland heads make 30 to 40 more horsepower then the original inline "Windsor" type heads do but the cam needs to have a minimal lift for them to work.
Clevelands start to make ungodly type power with cam lifts around .600" or more. Under .500" lifts, they are just like any other "grocery store" engines.