I just put in a new edelbrock performer rpm cam kit in a 350 with 10.25- 1 pistons and sportsmen II heads and 1.5 roller tip rockers. the lift on the cam is 480 intake and 510 on exhaust. The problem is that when I turned the motor over by hand, the exhaust valve hits the piston. How do I know how much lift I can use with out hitting the piston?

its not gross lift, but area under the curve that cuases the problems.
More duration can effect your valve to piston.
YOu need .100" to be safe on the exhaust, and .080" on the intake.

How are you measuring it now?

Are you sure the cam is installed correctly? Having it advanced too far will decrease the exhaust VTP clearance. Are these new pistons? Does the valve fit into the relief correctly?

if i remember correctly,that's a .525 lift cam.are youusing stock pistons?try modeling clay on the piston tops to see where the valves are making contact.

Make sure the cam is installed correctly. The dots on crank and cam gear should both point up on #1 - not pointing at each other. Also, are you sure you're not binding a spring - be sure to check that since 'coil bind' can fool you into thinking a valve is contacting the piston. I second the clay advice.

-dnult

You sure your not running into coil bind on your springs? Thats really not that high lift of a cam so im assuming your duration isnt real long either, im running a 0deck block, .040 quench, pistons with 5cc valve relief flattops, with heads milled to 60cc and a 302/310 268/278 .560/.570 cam in my 350 and i had alot of room to spare, based on that it seems that it would have to be somthing else? Before you go to the trouble of claying your pistons, check you valve springs when it locks up to possibly rule that out. And Dnult, the dots point at eachother

Actually guys, the dots could either be pointed at each other OR both pointed straight up. Think about it ;) If you want me to explain just ask tongue.gif

It does sound to me like the cam isn't installed correctly. The springs on the sp2 heads should be able to handle this cam with no trouble, but definately worth checking. Also check to see if maybe the rockers are binding on the rocker studs.