Dave,
Use the gasket that will give you a total stack as close to .040” piston to head as possible. Most OEM engines rate @ .020”- .025” in the hole from the factory. A .027” gasket will put you from .047”-.052”, acceptable but not ideal.

If you parallel deck the block to remove taper you also have the benefit of an improved gasket surface and more consistent cylinder volume. For example you deck to .015” with a .027” gasket your total stack is .042”, closer to ideal.

In the case where any combination of mechanical parameters renders your piston >.005” you will need to consider a gasket of .039” or greater.

These guidelines are for N/A engines.

Bob

I have a brand new Dart Big M. I guess without measuring the suface i wont know how much is going to be taken off at the machine shop, thus wont know what thickness gasket to buy until after that, correct? Is there any difference to using flattop pistons with a small chamber head (110cc) as opposed to using a dome piston and larger chamber head (119cc) if they both give the same compression ratio using the same manufacturer of cylinder head? One part of me wants to keep what i got (-4.5cc pistons) and go with 110cc head (which is harder to find but Canfield offers it without a surcharge) and the other half wants me to sell the pistons and buy dome top and go with AFR 119cc heads. Problem for me is price difference $$. Between the 110cc Canfields and my flattop pistons and the 119AFR and some dome pistons with both being around 9.5:1 CR is it really worth the extra money for what possible gains i would get. BTW, i'll probably use the Victor Jr Rect Port.

When I ordered mine, AFR had a 8 week backlog. Keep the Canfields, you'll never notice the difference.

The Canfield head on 502 to 540 CID engine works very well. That port actually CC's to about 300 cc so the heads have great velocity. The head was designed by Joe Petelle of HVH and does make good power.

I will have to agree with the others that have posted for a 502 that is going to see 5500 or so rpm that cam is a little big on duration but about right on lift, if the lift numbers were flipped.

[QUOTE=daveintexas;2055426]I have a brand new Dart Big M. I guess without measuring the suface i wont know how much is going to be taken off at the machine shop, thus wont know what thickness gasket to buy until after that, correct?

Tell them you want the piston down .010 -.012 in the hole and what parts you are using. Then get the .027 gaskets. Tightest quench possible is best for many reasons.

BT :cool: