I read that I measure the quench by adding the compressed thickness of my gasket to the deck height. How is this right? That would mean that if I had a deck height of .025 then I would have to install a .015 gasket to get the recommended .040. The .015 gasket would give me 11:1CR.

Something ain't right

The numbers are right, you just didn't plan for the quench. Compression is total volume, piston at bottom dead center to total volume, piston at top dead center. When you build for quench you need the right head chamber - piston - deck height - gasket combination to give you both the desired compression and desired quench.

This isn't an engine I built. These are GM crate engines from the factory. For instance... the ZZ4 has a .025 deck height and a .051 gasket. Thats .076 quench....from the factory. Why does this work so well, if the desired quench is .040?? Am I really going to benefit if swapped to a 64cc head and used a .015 gasket? That would give me .040 quench but thats a scary thin gasket.

The 1094 WILL seal great, assuming your deck and heads are flat. I put 2 coats of spray on copper seal on both sides of the gasket.

As for quench...that's one of those lil gray areas. They say that if your quench clearance is less than .060 or so that the engine will be more resistant to detonation than if it is larger

The ZZ4 has a .076 quench (at least I think the deck height is .025..anybody know for sure?) and I've ran that engine to max RPM many a time with no detonation. So should I really be worried when I go to buy new heads? I want the Trick Flow 56cc chambers. They out flow the RPM heads, come with hyd roller springs, will give me 10:2CR with a .041 gasket but my quench would be .066. If I'm higher than that now without detonation then I shouldn't worry... right?

The RPMs, with a .015 gasket would give me 10:1 and a .040 quench. But they don't come with strong enough springs and don't flow as much air as the Trick Flow.... see my problem?? I'm ready to buy new heads right now but I need to get this issue resolved first.

The 1094 WILL seal great, assuming your deck and heads are flat. I put 2 coats of spray on copper seal on both sides of the gasket.

As for quench...that's one of those lil gray areas. They say that if your quench clearance is less than .060 or so that the engine will be more resistant to detonation than if it is larger

You say .060" and most say .040". My DZ is at .053" per JM's recommendation and it works just fine unless there is silent detonation going on. There is no audible detonation. It must be a real gray area.:thumbsup:

Fluid Dynamics and Thermodynamics Rule!

Quench provides turbulence to the mixture inside the combustion chambers. The turbulence prevents hot spots from getting hot enough to detonate spontaneously (detonation). It is one of the contributing factors that allow 1.2 horsepower per cubic inch in the small block, that the big block with it's semi-hemispherical designed combustion chamber can not match. Some head designs (the Vortec in particular) do not rely upon quench as much because they have a kidney shaped combustion chamber as opposed to the traditional wedge shape. It uses the compound curves of the bowl area and the chamber to swirl the incoming gasses to create turbulence.


Larger Dave (retired engineer)

Factory engines are not designed around a .040 quench and don't exibit detonation as designed. Having a .040 quench is a way of improving the burn pattern and helps when running more compression. There are lots of factors that determine if an engine will run on pump gas and not detonate. Valve timing will effect dynamic compression which is a key factor in if an engine detonates also. Dynamic compression is the compression being taken once the valves are closed. As the piston moves up off bottom dead center and both valves close earlier you would have a higher dynamic comp ratio and need high octane. Close the valve later and you get a lower dynamic comp ratio and can run lower octane... A good street performance engine balances this to make power and run on pump gas.

I'm really a rookie at this but can tell you there is some great info on all this if you do a few searches...

So anyone want to pick a head from the two mentioned?

Trick Flow... more flow, more HP, 56cc & .041 gasket = 10.2CR with a .066 quench (I have .076 now..no probs)

Edel RPM....less flow than above, 64cc & .015 gasket = 10:1 with a perfect .040 quench (but *less* power and scary thin gasket)


Opinions? I'm on the fence here and I'm ready to buy...:(

My choice form info given by others here, would be the Trick Flows. If .076 works, then .066 will work also.

If it ain't broke, don't fix it!

Thanks Dave, Dennis, and everybody for the statements, I'd kindda forgot those from school. Now I'll be thinking those all day long.......

You say .060" and most say .040". My DZ is at .053" per JM's recommendation and it works just fine unless there is silent detonation going on. There is no audible detonation. It must be a real gray area.:thumbsup:
.060" or so is the max for any quench effect to start. .040" is the smallest you should make your quench area, any smaller runs a risk of pistons kissing heads, not a good thing.

All that said, in this instance, I'd go with the TrickFlow heads, quench be dammed.

As an aside, yesterday I put some 89 octane in my 383 (instead of the usual 93) No detonation at all. This is a 6" rod 383, 9.6: comp iron head motor with .040 quench and optimal timing.

Ok. I've learned all I need about quench. So, this is my last question...
I've been told a better head choice for a high performance **street** car would be the Trick Flow 195cc 62cc chamber head. This outflows the Trick Flow 175cc I mentioned earlier and the chambers are small enough to use a .028 gasket and get 10:1 with a better quench of .053.

My question is.. do you think the 195cc is too big for the street or should I stay with the 175cc. Its a ZZ3/ZZ4 crate engine with an RPM intake, 228/234 dur. and .529 lift 106 lobe separation hyd roller cam. 3:73 gears Turbo 350 w/ 2500 stall.

CR is the same..so 175cc with more quench or 195cc with lower quench?