Thread: 327 rebuild

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Not trying to be a smart ass, but with the information you provided at this point, the best answer anyone can give you is as Dave said...."depends". The small valve/small chamber heads will increase compression and the small valves will make better bottom end torque but run out of steam quickly above 3500-4000 RPM. The small chamber heads could potentially raise compression too high to run on pump gas. The bigger valve heads will breathe a lot better but the compression drop may make the engine a real pig.

I would start by figuring out what the compression ratio will actually be with various combinations. To do this properly you will need to know the actual volume of the combustion chambers. Do not go by what the factory advertises the chamber volume as these old heads they are usually anywhere from 2-6 CCs larger than claimed. It’s best to actually CC the chambers to find out…..and you will need to do each chamber, as they will vary within the same head. Although not as fancy as some, JEGS and Summit both sell economy CC kits that will suffice for doing this

http://www.summitracing.com/parts/po...1155/overview/

JEGS Economy Cylinder Head CC Kit - Free Shipping on All Orders @ JEGS

After that you will need to figure out the volume of the piston valve reliefs and if the edge of the piston is beveled what that volume is along with the volume based on how far down the piston is in the cylinder at TDC. Do not assume the pistons are flush with the deck. You will normally find they are a few thousands down in the bore. The way to find this is with a depth micrometer or in a pinch a straight edge and feeler guages.

Finally you will need to know the compressed thickness of the head gasket.

With those values in hand find a decent on line calculator and plug in the numbers to come up with the real static compression ratio. From that point you can play with different thickness head gaskets and milling (figure .007” per CC as a ball park figure for milling ) to fine tune the compression.

The final step would normally be taking the real static compression ratio and plug that along with proposed cam profile into an online calculator to determine dynamic compression.

Sometime in this process you will also need to determine what grade fuel you will want to feed this thing to determine what you target compression ratio should be based on how you want to use the engine.

The Second Option

Go eeny meeny miny mo, bolt a set of heads on and see what happens.


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