How much can I lower compression by just changing the head gasket?
07-16-2009, 07:44 PM
#1
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How much can I lower compression by just changing the head gasket? Still mapping out a FI plan. Want to just have fun with the engine I have now, other than changing lifters (morel), springs, and head gasket.
I have 11.1 right now, and I believe that is with a .040 head gasket.
How thick can I go on the gasket to get the compression down? How thick would I have to go to drop it down into the 10.5 range?
Engine is a 402 with AFR 225.
I have 11.1 right now, and I believe that is with a .040 head gasket.
How thick can I go on the gasket to get the compression down? How thick would I have to go to drop it down into the 10.5 range?
Engine is a 402 with AFR 225.
07-17-2009, 12:24 AM
#2
You don't want to ruin your quench height, which is your piston-to-head clearance measured from the highest point on the piston which corresponds to the flat (non-chamber) section of the head for each cylinder.
Quench is best in the .040" range, +-.010". Any looser and you risk more detonation and any tighter you risk the piston hitting the head and breaking things. Since you are going FI you could probably open the quench to a max .060" since the FI makes up for some of the loss of turbulence induced by the tighter quench.
Bottom line: Use gasket thickness to final tune your quench, and change pistons to make large changes to your CR. If you are 11:1 now, there is no reasonable gasket change you can make to hit 10.5. Bite the bullet, do it right and change the pistons.
Or get heads with a larger chamber.
Jim
Quench is best in the .040" range, +-.010". Any looser and you risk more detonation and any tighter you risk the piston hitting the head and breaking things. Since you are going FI you could probably open the quench to a max .060" since the FI makes up for some of the loss of turbulence induced by the tighter quench.
Bottom line: Use gasket thickness to final tune your quench, and change pistons to make large changes to your CR. If you are 11:1 now, there is no reasonable gasket change you can make to hit 10.5. Bite the bullet, do it right and change the pistons.
Or get heads with a larger chamber.
Jim
