Engine Squish, quench help

Foot Hill

Dec 9, 2014
Hey everyone, got a new roller cam and I’m having my Edelbrock preformer 1.60/202 heads milled to remove the lock wire groove (about 10 k) going to cometic
Currently heads have about 0.30 piston to head clearance and Compression ratio is 9.25

I have chance to use thicker head gasket to get me back to @.030 again.
I’m wanting to make about 500 flywheel horsepower with boost so I’m asking the pros.
Is 0.30 too tight?
Would 0.40 be better?
What would be ideal?
Thanks in advance as I’m clueless in this area.
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Foot Hill

Dec 9, 2014
Either clearance is too tight. How did you measure that?
First off ..thanks for your reply!

I checked with The old head gasket and about half the head bolts torqued down (half torque) with clay on top of the piston I did it again today and came up with about.040- .045
The used gasket has a compressed thickness of .039 and I couldn’t fit a .005 feeler gauge underneath a straight edge across the block deck and top of piston
Basically deck height is even with piston (piston maybe a few thousand under)
So I guess that makes my squish easier to determine ?!
basically my compressed head gasket thickness ?

The Pistons are dished and fly cut and my valve clearances are fine
this is going to be a supercharger set up with around 8 to 10 pounds of boost.
The fel pro 9333 PT1 are .047 compressed thickness which would give me about .050 squish
is that a better squish number?
Or should I go to a Thicker Cometic gasket?

John Dirks Jr

5 Year Member
Jun 28, 2013
Go with a thicker Cometic head gasket. You don't need the compression with boost anyway. On my setup with Gt 40 (non P) heads milled .015 and block decked .003, I used .060 compressed thickness Cometics.
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Active Member
May 15, 2018
.041 of quench here, zero decked.

With a good set of rods I wouldn’t want to run and more.

Stock stuff I’d probably be more inclined to go for a higher quench number.
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Rt jam

Oct 17, 2015
Your method is solid. As for clearance I would recommend more. 0.90" is totally safe. The blower is not a factor here. Connecting rods and rpm is.
To just throw a bigger gasket in will solve your clearance issues but understand you will change the quench with this correction.

Every engine combination is different but years ago I had an 11 second Plymouth Road Runner with a 10.5:1 440 iron head engine. I swapped to a thicker gasket so I can put the engine in a truck. With the lower compression ratio I was hoping to use 87 octane but it ended up needing 91 and seem to detonate more than before with a lower ratio. Probably because I lost quench.
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Foot Hill

Dec 9, 2014
Ok. Thanks for all the input.
I checked again and looks like I have zero deck height
The pistons are dished and flycut and valve clearance is good with the used compressed .039 felpro
So, I can have whatever quench at this point
The standard felpro 9333pt1 have .047 compressed thickness so I’ll probably go that way.
The .051 cometic is tempting but a bit pricer and I’m thinking it might be nice to have the head gaskets be a “fuse” Incase I get detonation on a hot summer day ;)
And yes, stock block rods & crank (similar to Mexican) 1978 D8VE A3A casting.
Just my understanding that too much clearance might invite detonation.

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