Another compression question

[DannyC.]

I have milled a set of 906 heads .080". I suppose the compression was around 9 or 9.5 to 1 before . The queston, should I use pump gas or race gas for maximum performance?

[ROWDY]

danny...depends on how much overlap on the cam you have.the overlap can bleed off cylinder pressure at low engine speed but a 50/50 mix will work fine

[DannyC.]

Rowdy, I don't know that. How can I find out?Is there a # on the cam where I can have the specs. checked? I bought the motor assembled and thought I could add a little more power with machine work to the heads. All I know about the cam is the .525 lift. If I don't have the right piston to valve clearance, how can I correct that? And I would also like to go bigger with a roller cam. Could I use bigger springs to decrease the valve opening? Thanks for the helpful information. This is my first engine project and any helpful info.is appericated.

[ROWDY]

To check overlap grab a degree wheel and a dial guage.You may have to get somebody to show you cause its to hard to explain here.To check valve to piston clearance,the easiest method is the old plastacine trick.Put plasticine on the piston,refit the head with the headgasket and turn the engine over SLOWLY!!!!!!!do a full revolution of the cycle.If you feel it stop its hitting(of course)Measure the thickness of the plasta cine.90th is the minimum on the exhaust valveand not much less for the inlet.You can have the pistons fly cut to clear the valves but make sure the piston head is thick enough to suit.
If you know the maker of the cam and there is a number on the cam you maybe in luck.If you know the cam maker give them that number and they should be able to give you the specs.

[DannyC.]

Thanks again Rowdy. Yeah I know how to check the piston to valve clearance , but I was going to use modeling clay. I think the piston have all ready been cut, but I'm not 100% sure. Flat top piston have a cut away spot for the valve to fire, right? As far the cam, I'm almost certain its a Mopar Performance cam. So I'll check with my local mopar supplier and see if they can shed some light on this puzzle. Hey thanks again, this information will definitely com in handy.

[This message has been edited by DannyC. (edited February 06, 2000).]