If I have a standard bore at 4.000, how much clearance do the off the shelf head gaskets have? The reason I ask is that I am in the process of purchasing parts for an overhaul and I am thinking about using head gaskets on the thinner side, like in the neighborhood of .030~.035, to increase compression a bit. The online stores list everything from 4.010 to 4.210 bore. I’m guessing that you need to take core shift into consideration, but hell I don’t know, buy 4.030 and hope? I need to tap the knowledge well here before I do anything like that. Full disclosure: -1978 Ford 302 (the most gutless thing I have ever driven, but it’s supposed to have stock flattop pistons if my info is right.) -58cc heads that I bought for cheap. If flattops are indeed there, I don’t know if there is zero deck height or not, either way it is an improvement over the Thermactor smog heads on it now at 69cc. But now I’m getting into compression ratios...
looks like you can do that, you'll spend about 5 times as much for head gaskets as you have to.... The gasket with the hole the same size as the bore should work fine.
I don't think Ford small block pistons come up above the deck, so I'd go with the 4.010" bore gaskets and see how it looks before putting the heads on. I bet it will be fine. I first came up against this issue with an off topic Ford four cylinder. I don't like a gasket that is way bigger than the bore, I figure you end up with a deep groove that serves no purpose other than to increase the unburnt mixture due to quenching.
Your pistons are probably at least .030 to .060 down in the hole. .045 is real common. Most SBF head gaskets are 4.010 in bore diameter unless you get into the real high dollar stuff. Look at a 1011-1 or 1011-2 depending on what style ring you want to run and what actual head you have. SPark
Well the original post said 4.010". Re-reading the post now I'm not sure if the question is about the bore, or the thickness of the head gasket.
You've got to have the head gasket at least .030" bigger than actual bore size to allow for the lead-in chamfer that is cut on the top of the bore to ease ring installation....you don't want any part of the head gasket fire ring not in contact with metal....if it hangs out over the chamfer it will start to burn away the fire ring. 4.100" is the smallest common size to cover 4.000-4.060" bores. Cometic does make 4.030, 4.040, 4.060 and 4.080" for guys really into maximizing their compression ratio by staying as close to bore size as the block chamfer will allow, but you pay a pretty stiff amount to get those tighter fitting gaskets. You're better off worrying about your gasket thickness and how it figures into getting you close to an ideal quench figure of .035-.045" than you are to worry about minor compression losses or gains from diameter changes of the gasket bore. That ideal quench figure leads to better power, better efficiency/mileage, and better octane resistance.
Been a long time ago, but I remember a friend encountering the fact that SBF blocks have been built over the years with 2 different deck heights. If you use the pistons for the short deck height in the taller deck height blocks the piston will be down in the bore quite a bit and the compression ratio will be so low it "won't run out of a shower of shjt"
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