hammertime

iTrader: (1)

Old rule of thumb used to be .040" inch for good activity in the combustion chamber. I'm seeing people using gaskets that are .040" thick on these engines that are .006 - .008 above deck, leaving .032 - .034. Is that enough for an engine that could see 6500 - 6800 rpms?

TT_Vert

iTrader: (12)

yep, keep in mind as the engine heads up that quench will grow some. So you will probably be around .040" hot w/ a .032" cold quench

Dave

1989GTA

I have been doing a lot of research on the subject and the latest info I can find says .035 quench is a good number to shoot for. If you have aluminum rods or excessive piston clearance than that number should be higher. Me, I'm going for .035 quench with my new motor. This is on a 1st gen motor with aluminum heads, pm rods, vortex block and forged pistons.

DavidNJ

Vizard recently wrote that .025 is ok for cast iron block, cast iron head to 6800, adn .028 to 7000. It sounds like a hydraulic lifter LS1/2/6 setup may work with .025 or even less.

SStrokerAce

iTrader: (2)

Depends on how much piston rock you have as well.... a loose fit piston needs more quench.

Bret

DavidNJ

Vizard was using .0035 clearance with KB pistons. However that was a steel block. MadBill once calculated .019 might work. You would have to make sure the block was up to temp before reving it though.

67Ranger

iTrader: (16)

From what ive heared, .032-.040 was optimum on the small end, and anything between .050-.070 was bad, but if its bigger than .070 its as good as having a tighter quench. Not sure why on the higher side, but just what ive heared.

blackz93

iTrader: (2)

Doesn't make sense.

z-ya

iTrader: (1)

Got mine at .028 with .036 cometics on a stock shortblock. Runs just fine and has a
wide tuning latitude and good resitance to detonation with 60cc heads.The reason
they run shity at .050 to .070 is that the mixture traped in the quench does not contribute to combustion at those dimentions and becomes wasted.After the quench
reaches about .070 or so all the mixture can burn ,but you lose the detonation resistance and may not be able to run optimum timing etc.

SlickVert

iTrader: (5)

I am running a .040 cometic with pistons out of the hole .006 to .008 on a stock short block with ARP rod bolts, spinning to 7,300 rpm. I just removed the heads and you could still see carbon on the pistons under quench pads. I have heard when it real tight there would be no signs of carbon under the quench pads. So it looks like it could have been tighter.
Bob

speedracer5532

iTrader: (8)

My pistons are .011 thousandths out of the hole and I am running a .040 Cometic gaskets which gives a .029 quench cold spinning it to 7400 with no problems at all.

383ss

iTrader: (14)

well, I'm iron 6.0L with 5.7 heads, but I'm running .025 quench, thinking about running .021 since I need to order new gaskets.

DeltaT

iTrader: (5)

Just remember the consequences of too little quench is a mechanical stop and parts breakage. Tightening it up a few thou once it's right is not going to buy you anything, and playing around with sub-.025" could be like tossing a grenade around - sooner or later the pin is going to come out...

Jim

fast240z

Yea, what he said!

Why would someone want to play with this clearance? This is not something you improve your numbers on. All you have to do is insure that you have the proper clearance there (.040-.035) and move on. If you are super stock racing and you are restricted on the piston top allowed then you need to be somewhat more concerned with this. However, we can pick and chose the piston, head, gasket, rod lenght, etc to what ever we want.

Bottom line: insure you have the right clearances and move on.

Mark

hammertime

iTrader: (1)

Presumably then, an engine that has been honed for forged pistons and has the proper clearance at operating temp will probably be able to get away with a tighter quench than a stock low mileage setup using factory tolerances and cast pistons? I'm basing this assumption on SStrokerAce's post.

Basically trying to figure out the optimum setup when changing heads and cam to get the SCR and DCR where I want them.

DavidNJ

Since the parts shouldn't stress less with age, and high-cycle fatigue isn't an issue, age shouldn't be an issue.

The amount of stretch may actually be more with higher strength pieces. All steels have about the same elasticity, the stronger ones have a higher yield point. This allows a lighter piece, with a smaller cross section that will stretch more, to have the same overall strength.

The lower clearances increase are supposed to improve combustion and reduce detonation resistance allowing higher compression. If a cast iron block can run .025-.028", a low rev (below 7k) aluminum block should be able to run less.

Also note, I'm not sure piston to wall clearances (unless they are ridculous) should be an issue. Once hot, your piston should be within .001" of the wall.

However, you must be sure the block is hot before reving it. If the block hasn't expanded due to heat, the piston might hit.