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CAM selection help

847 Views 2 Replies 2 Participants Last post by  tattooedsgt
Is there a way to measure how big of a cam I can go with without actually having a cam. I was wanting to get a lunati roller with a .630 lift on the intake and exhaust. But i wanted to make sure that I would have good valve to piston clearance. I have 781 heads with i think is a 118 CC head.

Lemme know if this would work. Put a piston @ TDC. Put a glob of silly puddy on the piston. Install the head gasket and head with a few bolts and tighten down. Remove the head and measure the puddy. If im over .630 inch than I should be good to go? Right?:confused: I have large dome pistons thats why im asking. Any help would be great.
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You need to be aware that Valve to Piston clearance isn't the only parameter for maximum lift. You may want to check the flow bench numbers of your heads to see if more lift will be useful. Big Block valves are very heavy, so lifting them higher than beneficial will only tempt valve train instability

The valve doesn't come closest to the piston at TDC. It's actually about 8-14 degrees before and after TDC depending on if it's exhaust or intake valve. The intake is bigger so more likely to hit first, but because a lot of cams have more exhaust duration this may not be the case.

If you have plenty of clearance at TDC, you'll most likely have more at 12 degrees so most people check at TDC with the clay method and maybe check it without the height of the gasket for an extra margin of error.

Don't forget actual rocker ratio when figuring lobe lift to valve lift.

Don't make the assumption that big power comes from the biggest cam. Number ONE hotrodder mistake is overcamming the engine.

A guy I work with here is having a 454 built back in the states. He asked me to critique the combination. I took one look and said "the cam is too big for those heads". He was told it would make 800 hp. I said I'm guessing 600-630Hp.
I entered the data into my Dynomation 5 software and sure enough it predicted the same power. I picked a better choice for cam and the power went to 680. More power from a "smaller" cam. I told him to get to 800 he'd need better heads and then a different cam to match.
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