Cylinder Head Shims

I was going to buy new heads because I have to lower my compression ratio. The heads I have now have a 60cc combustion chamber and I need a 64cc chamber to get the compression ratio I want.

I saw that Fel-Pro sells copper shims to "return" shaved heads back to a pre-shaved condition. They are .020" at a 4.100" bore which equates to 4.25cc (exactly what I need). This lowers my compression ratio about half a point.

I have a couple questions:

1. Where do these shims go? Between the block and gasket or between the gasket and the head?

2. My heads have not been shaved so they will both move "out" and "up" approximately .014" (.020 X cos45º). Will this be a problem when mounting the lower intake?

Thanks for the help and if there is any reason why I should not do this, please let me know.
[addsig]

MIL-40034
Ford: 302/351W, 4.060 in. bore, .060 in. thick copper head gaskets.
$89.95 at Scummit.

FPP-1046
Ford: 302/351W SVO, .051 in. compressed thickness, 4.200 in. gasket bore, 11.7cc compressed volume, head gasket.
$86.99 At Scummit.[img]/phpBB/images/smiles/icon_tup.gif[/img]

I already have Fel-Pro head gaskets. (.039" compressed at 4.100" bore.)

Can I do that with the copper shim?

I assume you have a knocking problem? Increasing the quench/squish height usually makes the problem worse, due to the reduced turbulence in the combustion chamber.

I have no hands on experience with this, though, other than that I have no knock problem with my tight squish 10:1 CR 289.

Trooper, what are the measurements on your parts right now? How far in the hole is your piston? 3" stroke? What cam are you using?
[addsig]

No problems. Just trying to find a way to lower the compression ratio. Here is what I have:

4.030" bore
3.25" crank (331)
60cc combustion chambers
Pistons are all in the hole .007" to .009"
-14.2cc dished pistons
.039" gasket at 4.100" bore
9 psi Powerdyne supercharger
Have not chosen a cam yet

This works out to 9.04:1 compression ratio.

If I add .020" shims it drops it to 8.65:1 which I think would be great for a supercharger.

Should I just leave it alone and keep the 9:1 since my boost isn't that high?

Thanks!

9:1 is absolutely no prob with a SC. Higher static comp makes more torque with a SC than lower comp does. Leave it there and enjoy.[img]/phpBB/images/smiles/icon_tup.gif[/img]

Thanks, 1 Bad 88 GT! Again you've been a big help.

I just found out my compression ratio is slightly lower than I thought. I forgot to take into consideration the area between the piston and the cylinder wall that extends down to the top of the first ring.

You measure "piston to wall clearance" down by the skirt. The top of the piston has a slightly smaller diameter.

This might not make it go down by much, but it sure won't make it go up any!