hey guys i was wondering if anyone could tell me what quench is? also whats "good" and "bad" quench? thanks

 

Good quench is just the right amount. Bad quench is too little or too much. That's the simple answer, but I guess you weren't looking for just that!
Your quench area is the space between the flat part of the top of the piston, and the flat portion of the head. As the piston starts to come up to TDC, the air/fuel mix starts to burn. As the piston hits TDC, the burning air/fuel mix in the quench area gets squished out into the combustion area of the head (the raised area where the valves and spark plug is). This causes a forced turbulence into the combustion area, which is a good thing. So let's say your piston at TDC is .010" below the block deck, and you're using a head gasket with a compressed thickness of .030". That gives you a quench area of .040". That's a pretty tight dimension, since you have to figure in some stretch in the rotating assembly, and the piston could actually smack the head at extremely high rpm's. A safe rule of thumb is a quench area closer to the .060" range. An engine builder who's good at what they do should be able to tell you how much you can safely get away with.

 

alright thanks that helps me out a lot, my piston at TDC i believe is below the deck .020" and i'm using a gasket which is .041" thick, so i should be right there, alright that clears things up a lot, thanks again

 

I've always heard that at or below .040 is where you want to be with quench.

 

You saying .040 or less? That's the total clearance between the flat part of the piston and the head, on a cold non-running engine. On average, a quench area of .035 will make the pistons come very close to smacking the heads at higher rpm's.
There are a few things that factor in piston to head clearances such as...connecting rod material (aluminum can stretch more than steel), tightness of pistons to the cylinder (piston rock), rod bearing tolerances, overall engine temperature, and maximum engine rpm. And then don't forget to figure in a small additional amount of sloppier tolerances as the engine wears.
.060 would be the maximum you would want to go (if you needed to), and less quench is better for performance. But, all that is why I said a good engine builder would know what you can get away with.

 

Fel pro gaskets generally run .039", .041", and .051" compressed. Unless you are referring to a shim gasket which are .015". I definitely would not go under .040" quench. When I had my block decked I told them to shoot for 9.005" deck height, leaving me .044" quench w/ a Fel pro .039" gasket PN 1010.

 

Yeah, most of the sites I've read about quench talk about .035 - .060 at the max with getting lower equaling better. One of my friends who builds these monster small blocks always shoots for around a .040 and if he can get it just below that he does. I heard that .025 - .030 clearance is good at cold with steel assemblies. By no means do I consider myself a master engine builder either.

Mine personally is higher than that at .050 with gasket and what's in the hole. I'm doing a head and cam swap here in the next few days or so and want to get it around a low .040 myself. I'm having a really good shop that does engines for NASCAR teams (that's their main bread and butter) do the head setup. When I drop the heads off I was going to ask them about the quench and what to look for to get a sweet spot with mine. The main thing I'm worried about with mine is piston to valve clearance with the new cam.