Rembrant Posted December 27, 2021 Share Posted December 27, 2021 Gents, I need to pick up a set of head gaskets for my 302. I'd like to get it buttoned up this week. Does it matter if the gasket is 0.039", or 0.041", or 0.047" thick? Totally stock street engine, but bored 0.040" over. Heads have been resurfaced and block decks have been resurfaced. I don't know how much was removed between the two...I'm assuming somewhere between 0.005" and 0.010" based on previous experience. The Fel-Pro stock replacement gaskets show that they are 0.047" thick. From the little bit of reading I have done, it looks like the originals were 0.040"-0.041", but I'm only going by internet hearsay. I'm just curious how much it matters and how much I should care lol. If there's anything in-stock locally, it's likely to be stock-ish original replacements, and nothing more. I'll order something specific online if I need to, it's not a big deal, but just wondering what you guys recommend for preferred head gaskets and preferred thickness. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 28, 2021 Share Posted December 28, 2021 I think it only matters when you are trying to get the compression ratio spot-on, or if you are trying to get "quench", which takes the thinnest headgaskets. In your case I'd go with the stock replacement ones from Felpro. Link to comment Share on other sites More sharing options...
mat in tn Posted December 28, 2021 Share Posted December 28, 2021 I think it only matters when you are trying to get the compression ratio spot-on, or if you are trying to get "quench", which takes the thinnest headgaskets. In your case I'd go with the stock replacement ones from Felpro. well now that is almost a loaded question. ask that question in a room of ten engine builders and you get twelve different answers. i always start with purpose. engines are always purpose built. even if the purpose is to be general use where good enough across a wide range is the goal. i generally will say to stay with stock size on stock rebuilds. if the block was decked and the heads milled. knowing how much is important when making these decisions. often the piston tops out a few though below the deck and that reduces compression but quench also. i like quench spec to be 35-40 thou. if the pistons are 5 below deck i would like a 35 thou gasket, where if the piston is at deck or a thou above i would be wanting 40 thou gasket Link to comment Share on other sites More sharing options...
85lebaront2 Posted December 29, 2021 Share Posted December 29, 2021 We went through this on Darth's new engine to get the compression I wanted without being too high. I have a compression ratio worksheet I downloaded. I will send it to Gary and you, that way if Gary wants to add it to the site he can. There are several variables in addition to the normal bore diameter, combustion chamber volume etc. Link to comment Share on other sites More sharing options...
Rembrant Posted December 29, 2021 Author Share Posted December 29, 2021 We went through this on Darth's new engine to get the compression I wanted without being too high. I have a compression ratio worksheet I downloaded. I will send it to Gary and you, that way if Gary wants to add it to the site he can. There are several variables in addition to the normal bore diameter, combustion chamber volume etc. Thanks Bill, I used that chart and another one online and my compression comes in right around 9.0:1 for this engine, and I'm fine with that. I had to make a couple of assumptions, like comb chamber CC size and piston valve relief size as I'm not going to go through the trouble of measuring them. Worst case it might be 8.9:1, and on the high side it might be 9.1:1, so either way it's fine for what I want to do with it. Thanks gents. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 30, 2021 Share Posted December 30, 2021 We went through this on Darth's new engine to get the compression I wanted without being too high. I have a compression ratio worksheet I downloaded. I will send it to Gary and you, that way if Gary wants to add it to the site he can. There are several variables in addition to the normal bore diameter, combustion chamber volume etc. Bill - Take a look and see if you approve: Documentation/Engine/Compression Ratio Calculator. I added the # of cylinders input and changed the calculation to use that. And I added a cubic inch result in addition to the cubic centimeter result. Thoughts? Changes? Link to comment Share on other sites More sharing options...
85lebaront2 Posted December 31, 2021 Share Posted December 31, 2021 Bill - Take a look and see if you approve: Documentation/Engine/Compression Ratio Calculator. I added the # of cylinders input and changed the calculation to use that. And I added a cubic inch result in addition to the cubic centimeter result. Thoughts? Changes? Looks good to me. This is what I used on Darth's new engine, in fact the numbers are from that build. Gasket thickness is compressed thickness and obviously the larger the bore, the bigger effect the gasket thickness has on compression ratio. Hopefully this will help some people with engine builds. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 31, 2021 Share Posted December 31, 2021 Looks good to me. This is what I used on Darth's new engine, in fact the numbers are from that build. Gasket thickness is compressed thickness and obviously the larger the bore, the bigger effect the gasket thickness has on compression ratio. Hopefully this will help some people with engine builds. Thanks, Bill. Link to comment Share on other sites More sharing options...
Lima Delta Posted January 1, 2022 Share Posted January 1, 2022 Thanks Bill, I used that chart and another one online and my compression comes in right around 9.0:1 for this engine, and I'm fine with that. I had to make a couple of assumptions, like comb chamber CC size and piston valve relief size as I'm not going to go through the trouble of measuring them. Worst case it might be 8.9:1, and on the high side it might be 9.1:1, so either way it's fine for what I want to do with it. Thanks gents. I was just debating this very thing with myself. I have a set of the Fel-pros that came with a gasket set and which compress to .047. Problem is, after doing the math back and forth a bunch, to get into that ideal quench zone I need to go with something more like this: https://www.cometic.com/products/C5514-027 I think these are something north of $100 each with a 6 week pre-order. I had to ask myself if it was really worth it for me to spend an extra $200+ to get a .020" closer fit for my cylinder heads on a street engine that will only have about 8.5:1 compression with the thicker gasket. I don't think so. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 1, 2022 Share Posted January 1, 2022 I was just debating this very thing with myself. I have a set of the Fel-pros that came with a gasket set and which compress to .047. Problem is, after doing the math back and forth a bunch, to get into that ideal quench zone I need to go with something more like this: https://www.cometic.com/products/C5514-027 I think these are something north of $100 each with a 6 week pre-order. I had to ask myself if it was really worth it for me to spend an extra $200+ to get a .020" closer fit for my cylinder heads on a street engine that will only have about 8.5:1 compression with the thicker gasket. I don't think so. How far down in the bore are your pistons? If they aren't pretty much at deck height you won't get to the ideal "quench" with any gasket. That's because you need about .040" between the piston and the head to have good quench. Summit says you should be at "0.035 - 0.045 in." So with even the thinnest gasket you mentioned of .039" you can't get there w/o being zero-decked. Link to comment Share on other sites More sharing options...
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