I've run anywhere from .038" to .055" "squish" distance, (piston to head) on previous engines. For my current combination I just ordered a pair of MLS Cometic head gaskets that will bring my quench height down to .035" so I was wondering what you guys like to run. Feel free to share any horror stories if/when you chose to run a piston to head distance that turned out to be inadequate.
How much quench distance do you like to run?
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how far down in the hole are your pistons measuring??
are we to assume you are at zero deck height??
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WJ went to school with a friend of mine & he told him once that if you can't see a mark from the piston on the head you're not making power. My friend also said WJ had quite a sense of humor (never would think it from his interviews years ago) so you never know but one thing was for sure he made power.
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5,678 Posts
I have ran as tight as .028" and as much as .064" 7500+
I found more difference in chamber shape than piston to head clearances.
This is for the SBC engine.
I currently have .039" head gasket and .013 piston down the hole and 57.5cc chamber head.
I let a guy drive it the other day and he can't drive. Des not know when to shift.
My engine will rev until it blows and he went over 7500rpm. I seen the tachometer at 7800.
He was no longer allowed to take the shifter out of D.
Actually he will no longer drive my car at all.
Did not hurt anything but not something I wish too see often.
That is a hydraulic flat tappet deal and I had another guy go 8500 rpm twice with a solid flat tappet I had.
Just buried the tachometer needle.
At high rpm I am more concerned with valvetrain stability than piston to head clearances.
I found more difference in chamber shape than piston to head clearances.
This is for the SBC engine.
I currently have .039" head gasket and .013 piston down the hole and 57.5cc chamber head.
I let a guy drive it the other day and he can't drive. Des not know when to shift.
My engine will rev until it blows and he went over 7500rpm. I seen the tachometer at 7800.
He was no longer allowed to take the shifter out of D.
Actually he will no longer drive my car at all.
Did not hurt anything but not something I wish too see often.
That is a hydraulic flat tappet deal and I had another guy go 8500 rpm twice with a solid flat tappet I had.
Just buried the tachometer needle.
At high rpm I am more concerned with valvetrain stability than piston to head clearances.
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I aim for .040, but .005 up or down is fine.
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Automatic or manuals trans? Autos don't miss shifts but sticks can! Steel or aluminum rods? I'll assume steel rods, AL rods will stretch and need more room. As another fella mentioned, a lot depends on the combustion chamber shape. I like 0.040" quench and zero deck pistons on iron blocks. Aluminum blocks grow more so at least 0.005" out of the hole is better.
Nope. Never assume anything. The pistons in my current combo are .008" in the hole, and I chose .027" MLS Cometic head gaskets.
Are you comfortable with merely .028" of squish because you're using hyper pistons? I'm guessing that is the reason since hyper pistons call for only .002" to .0025" piston to wall clearance, and therefore will likely exhibit less piston rock than standard cast pistons, or forged pistons will.
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Yes, block was decked to 9.010 but the stock 4.3 v8 rods are longer than I first thought and put me at 0 deck. Already bought the GMPP .028 head gaskets in anticipation of .038 quench. I might change them depending on final head cc but I want to keep compression up.
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Performance engines usually 0 deck and .039” gaskets. But sometimes I have ended up with pistons .005” above deck or below.
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I can't believe Jim Moore hasn't chimed in.
He likes to tell about one version of his engine that left witness marks on the heads from the tops of the piston.
That's close!
But, as he says, it keeps the rods from stretching
He likes to tell about one version of his engine that left witness marks on the heads from the tops of the piston.
That's close!
But, as he says, it keeps the rods from stretching
LOLOLOL!!!!!! That's hillarious!!!I can't believe Jim Moore hasn't chimed in.
He likes to tell about one version of his engine that left witness marks on the heads from the tops of the piston.
That's close!
But, as he says, it keeps the rods from stretching
Uh ho, Marcus and Nitro, you guys sure caught my attention with your explanations. I didn't even realize that pistons can vary as much as .006" or even .010" within the same block!!!??? I must confess that I only measured two of them, and both were in the same cylinder bank. I better go ahead and measure all of [email protected] before I go using such a thin head gasket. Thanks for the heads up on that!!! Worse case scenario might be that the two pistons I measured are the lowest/deepest [email protected], and according to what you guys are saying, it's possible for the highest pistons in the block that I have can be .002" above the deck, which would make the quench height merely .025" which wouldn't be good as far as I know.
1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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Billy if your block isn't square (from what my engine guy says) you can have pistons down different
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