Camshaft sizing help

[496 polara]

The only way to be confident they won't hit is to measure. That being said I would be surprised if there was an issue on such a small cam. Lots here smarter than me,hopefully they will chime in. @PRHeads spec'd my cam and has forgotten more than I will ever know on camshafts.

 

[Krooser]

Measure the combustion chambers, how far in the hole the pistons are. If they are .100 down you would be wise to limit the cam size because a low compression engine won't like a big cam.

My go to cam guy is Mike Jones @ Jones Cam Tecnologies. I stay away from all the big name cam outfits that sell cams ground by big factories in Michigan then get put in their box.

You don't need a custom cam but you DO need professional advice. Get on the phone but don't call Memphis.

 

[PRHeads]

Once the new heads are on hand, pull one of the old heads off, and using a head gasket of the correct thickness ……..
Put a piston at 10*ATDC, remove one of the intake valve springs, place the new head on the block(snug it down with a bolt or two), and measure how far the valve can open before it contacts the piston.
This is the valve drop.

Once you have that number you can get an idea of how much duration you can run without having valve to piston clearance issues.

For example, a Comp XR280HR, in at 106 and using a 1.5RR will have about .170 valve lift at 10*atdc(closest point).
You’d like at least .060” clearance, so you’d need at least .230” valve drop at that point for that cam to work.
Dropping down to the XR274HR would add about .020” of clearance.

While not great for compression or power, pistons sitting farther down the hole provide more clearance for longer duration cams.
The typical deck clearances for BBM flat tops that don’t have valve pockets range from about .050”(rare) to .150”.