Stroker2112

Would you rather have a great quench at .030 or a safe quench at .041?...


This is my dilemma....

I have .010 out of the hole
my heads(CNC'd LS6 243s) milled to 62cc
valves are stock
the cam is a torquer2 (.595/598)
stroke 4.000in, 6.125 rods
bore 4.030

On paper, a .040 cometic gasket sets me up with an approx 10.5 SCR, and a 8.5 DRC, and a quench of .030. However, when I do the clay PTV excercise....I'm getting results all over the board. ..as tight as .03 and as big as .140. I'm convinced that I will never get an accurate measurement with my lack of experience and limited tools/resources. My question to the entire community is...

Should I just get .051 thick gaskets and not worry about it?...


Stroker2112

Patrick G

iTrader: (14)

There are many people running .040" gaskets with pistons .010" out of the hole (myself included). It's about as tight as you'd want to run it. But your P to V looks to be the bigger issue here. Are you willing to fly-cut? If not, then you may want to clay a little more before you make your decision. Piston to valve contact sucks worse than losing a few ponies.

John02SS

iTrader: (47)

I'm running 40's with the pistons 11 out of the hole. No problems here!

Tony Mamo @ AFR

iTrader: (13)

There are actually a few things to consider when your talking about quench distance (piston to head deck)....the most important being what type of piston and how much piston to wall clearance is there. One of the reasons our beloved LS1's can tolerate tighter quench distances is that the factory pistons which make up the bulk of the builds we see here have extremely tight piston to wall clearance which prevents alot of piston rock....the looser the clearances the more rock you will have and the more you should compensate in quench distance to prevent one side of the piston hitting the head deck under operating conditions. Another factor is the LS1 aluminum blocks which will expand more than a cast iron block also having the effect of somewhat loosening the tighter quench figures...(due to the block literally growing slightly when its hot). Bore size also plays a small role here as well.

All that mumbo jumbo aside, most of the LS1 builds you will find here that are trying to maximize the quench distance are running as Patrick already stated around .030-.035

Most common is the typical factory slug running about .007 out of the hole and switching to the thinner .040 Cometic gasket (yielding a quench distance of .033 obviously). With custom pistons, larger piston to wall clearances, and/or very large bores you might want to stay on the higher side of that range (or even slightly more if your running .005+ piston to wall). Slightly more quench isn't going to hurt things very much, but tagging your cylinder heads with all your high dollar pistons at high RPM would certainly not help power and cause reliability concerns).

You know you got it right if you take the engine apart after it's been running awhile and see all the carbon almost perfectly clean on the quench pad of the head and one side of the piston....of course with signs of little or no contact between the two.

Tony M.

PS....I know one shop that tried running close to .020 and am told didn't have any contact, but the engine wasn't running very long and I believe when it went back together a thicker gasket was swapped in to be a little on the safer side (a GOOD move)....I am shocked there wasn't signs of contact at .020 but wouldn't ever consider running that tight either way and didn't personally see this motor come apart to validate this data one way or another.

racer7088

I've worked on maybe ten engines that were supposedly running like .030 quench as well and most were more like in the .045-.055 range when I actually checked the decks for real. I would not run anything at a real .030 quench on the street with a forged piston. There is not any real benifit that I've seen but like Tony said you might have some issues if you run it too close and start hitting. Some of these stock LSx engines are .011 out on one side and .003 out on the other anyway when you really check them all day long like we do!

OTOH if you really know that every piston is right in every single hole and the decks are straight and true and are not leaning and you have no previous contact you could tighten up to Patrick G level .030-.035 quench and maybe get by with it but I'd stay at least .035 myself. I just haven't seen any real gains from trying to run it ultra close and we aren't building comp eliminator engines here that need every little thing and compression too. But hey if everythings right go for it and then check up on it too every once in a while and don't pull any 1-2-1 shifts after tightening it up that much!

PREDATOR-Z

.035> .040 for the street.
Looks like .045 gaskets will do you good.