Tim81

Please help me My question is if you are running stock iron 76cc open chamber heads does the amount of quench really matter? I am putting together a 350 with Flat top pistons. This is my first build and I have over looked a few things. My piston pin height is 1.54 so therefore I'm sitting about .045 in the hole, if I use the .040 head gasket that came with the kit I bought then my quench will be at .080+ which I know is bad. My CR is 8.8:1 with a DCR of around 7.9:1. If I use a .015 shim head gasket the best I can hope for is a quench of .060. This engine is for a daily driver not going to be driven for performance, with that said I would still like to use pump gas. With open chamber heads is there really any benefit to running a .060 quench versus the .080?

Thanks for any and all opinions Tim

Solid LT1

Go with the 0.015" gasket 0.080" is too big a gap, it will effect HP/Torque and mileage, all will suffer. I usually shoot for 0.040" quench but have run as tight as 0.035" and as loose as 0.050" in my builds.

Tim81

Solid Lt1,

Thanks for your input, I know .060 isn't very good but I hope it prevents any detonation problems. Tim

TheSkunkWorks

Just seconding Solid's advice.

Indiancreek

Has the block been decked at this point? I'd like the range solid is talking myself. If it hasn't been decked at all, tear it back apart and have it decked some.

jackson

importance of quench is inversely proportional to fuel quality; I don't see favorable trend.

I'm guessing ... those 1.54 flattops are probably really cheap budget pieces ... maybe $50-$80/set sort. If so, consider pulling those out ... pay the shop to press off & on some others with 1.56 compression height.

You might also consider some with a small dome such as federal mogul sealed power p/n H618CP ... positive dome volume +3.5cc, ch 1.56". Fleabay under $170.

federal mogul compression calculator
http://www.fme-cat.com/Calculator4.aspx

fyi ... felpro 1094 gasket (0.015) volume is +3.2cc.

larrywalk

The normal compression height for a 350 piston is 1.56"; I don't know why some vendors are selling 1.54" CH pistons unless it's to accommodate blocks decked more than once, or to permit a 3.50" stroke.

By all means, select a head gasket to keep your quench at .035 to .045".

Tim81

I really apprieciate all the good feedback..Thanks to all. I am leaning towards the idea of different pistons, the only thing holding me back is something I can't predict. What advantage will a .040 quench give me over a .060 quench? Is it worth $300.00 for the difference? Having the decked cut is not in the cards.
Tim

cardo0

I don't anyone that has that much dyno experience to know at what compression ratio quench becomes effective. But i recall D. Vizard mentioning something like close to 9.0 c.r. better results from quench can be seen.
But for your combo the more compression the better and even that small amount from a tighter head gasket will help your performance - no matter what size your cam is.

Go for the steel shim Tim - and save some $$$ even on just the gasket,
cardo0

Manuel Azevedo

In grocery getter cars they are lowering the piston in the bore to keep compression the same some what because of the over bore and head and block decking done in production type rebuilds, sucks for performance though.

Tim81

Thanks Cardo0 and Manuel, I feel for my application I'll go with the smaller head gasket and see what kind of results I have. It just has to run well with no pinging. Tim