blue thunder

I am trying to fine tune my squish (quench) to .040 to .045". I currently have .010-.012" deck height and run the 1027 felpro gasket which is .039" compressed thickness. This gives me a squish of .049-.051". I would like to take .005 to .010" off my squish via a thinner gasket. Anyone know where I could find a similar gasket to the 1027 (alum head version) that has a compressed thickness of .030 or thereabouts?

Also, how much performance do you think I would be sacrificing staying with my current gasket and the .049-.051" squish vs getting it right?

BT

ratman

try cometic im sure they can fix you up. they make arguably the best gaskets period.
http://www.cometic.com/#
here's the link give em a call. good luk.ratman

blue thunder

Thanks ratman. I was looking at them earlier today. Only saw a .040 for the mark IV 454.

Reed Jensen

You probably won't notice any difference if you are under about 13 to one compression ratio... If there isn't sufficient "quench" around the piston, then the possibility of detonation increases. At least that is my understanding. But,,, When you have a 4.5 in bore like a lot of BBC's.. You have to worry about piston "rock" taking some of the quench area as the piston tilts. If you have forged pistons that don't have an offset on the wrist pin.. the tilt is less . But I'd worry about the piston striking the head if you close it up too much, especially when the pistons are cool and haven't expanded to running size.

blue thunder

I run hypereutectic pistons so piston rock/slap at low engine temps should not be a problem. I always understood .035" to be minimum allowable with steel rods/psistons and rpms not exceeding about 6500rpm. In a 5500 rpm marine application with hypereutectics I would think you could tighten it up even more from there. That is why I chose .040" as a goal squish distance.... plenty of safety margin. What I am trying to do is equalize burn rates between cylinders. A funcional squish should do that and I would think that the lower the compression the better the affect would be... not for sure though. I run about 9.5.

mcollinstn

The less squish, the more resistance to detonation.

BBC "best" squish is around .035"
Closest "safe" squish is around .025", but gains no advantage over the "safer" .035".

8.5:1 motors? It doesn't really make a rip.

Crazyhorse

I'd definitely argue that Cometic is the best as Merc has done extensive testing on them without great success. FelPro still seems to be the best head gasket around.

blue thunder

I dropped a valve in one engine july 4th last year. I was able to get by with a .010 bore on the cylinders and decked the block to .010 deck height. This engine gained significant power relative to the other undecked engine. Maybe 300rpm. The only significant changes would have been the improved squish (was over .030 deck hgt) and slightly higher compression. The engine also became much more responsive to timing, which I like. The other engine does not respond much to small changes in timing. I equate this improvement largely to the equalization of the burn rate from cylinder to cylinder. Now due to equal burn rates, instead of one cylinder wanting 32* timing to reach full pressure, the next wanting 36 and the others all somewhere else, now they all want the same 34*. I think on a quench style engine setting this distance properly garners more than one thinks, regardless of comp ratio. Plus it is basically free!

Vendor for thin gasskets anyone?

BT

Infomaniac

I run pistons .005 in the hole and .036 Cometic gaskets for .041 quench. .036 is a thin as they make them.

That leaves .005 for the block to be serviced and then use whatever thickness gasket you want after that. .036 to .040

10x

The average marine engine will NEVER be able to tell the difference in .005 of squish. I'm sure that by rebuilding that other engine last 4th of July, the freshing-up of it, is making the difference that you're seeing. Also the .010 over bore is contributing a little too, but (VERY) little.

Maybe you need to drop another valve in the 2nd engine and copy the first one, then they should both be equal?