Is this quench distance too small?

[blackford]

SBF 331 stroker, aftermarket reciprocating parts including H beam rods. I have the heads off to do some work. The short block is still in very good condition. The engine sees 7100 RPM max. It's mainly a street build.

Pistons are .005 in the hole, but I put a few pistons at TDC and tapped each piston with a rubber mallet to rock it all the way one way or the other and it brings the edge of the piston up .007 above the deck. I had .039 compressed thickness head gaskets with 4.100 bore on the engine. In order to minimize the amount milled from the deck of the heads to increase compression, I was considering a Cometic MLS .030 compressed thickness head gasket with a 4.060 bore. Will my quench distance be too tight with the .030 head gasket? Thanks

[mag2555]

Here’s a rule of thumb on this, while you can, depending on the chamber shape and area loose some power with too tight of a quench, it plale’s in comparison to the HP you can not be having by running too loose of a deck clearance, not to mention having a greater detonation sensitivity.

.025” to .045” works just fine.

[Tuner]

Any sign on a piston of touching the head?

[blackford]

Any sign on a piston of touching the head?

Not with the .039 head gasket.

[Tuner]

Can you get a .035" gasket? I would use the .030".

[blackford]

Can you get a .035" gasket? I would use the .030".

.036 is offered, but would do little to minimize head milling so I would not bother.

So, in the traditional sense ignoring piston rocking effects, i'm asking if going from .044 quench to .035 quench is OK. So far it sounds like the answer is yes. My rods are H-beam Scat pieces if I remember correctly ( I bought them 20 years ago) with 7/16 ARP bolts (again if I remember correctly) and I would think the stretch would be minimal.

I was surprised that the piston, when rocked, would go above the deck by .007. That's more than I would have thought, but the block was cold and maybe the piston tightens up in the bore at operating temperature. This is the wildcard that makes me wonder if .035 quench (.005 in the hole plus .030 head gasket) would be OK.

So would anyone else like to chime in? Thanks.

[Geoff2]

Piston rock. The piston will expand in operation & take up that clearance.

[rgalajda]

"Pistons are .005 in the hole"

I would measure all four corners at minimum. Better to check all 8 pistons.

[KnightEngines]

7000rpm - I'd usually defer to .40" min quench.

[RDY4WAR]

I ran a 355ci SBC to 7200 rpm, 6" rods, 1.25" pistons, with just .026" squish. It was zero decked with Mahle .026" head gaskets. I acquired it that way and was supposed to be .039" gaskets with zero deck per the spec sheet. It never made a sound, ran strong, no signs of contact, etc...

Going from .045" to .035" will be just fine.

[skinny z]

I ran a 355ci SBC to 7200 rpm, 6" rods, 1.25" pistons, with just .026" squish. It was zero decked with Mahle .026" head gaskets. I acquired it that way and was supposed to be .039" gaskets with zero deck per the spec sheet. It never made a sound, ran strong, no signs of contact, etc...

Going from .045" to .035" will be just fine.

I suppose we tend to like the answers that suit our particular situation and this answer does just that.
SBC, 6500 possibly 7000, 4032 flat top piston, .008" deck and the same Mahle .026" gasket. Fresh short block.
That'll be .034" at a minimum (pending measuring 7 other cylinders).
Thanks.