FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: c9zx on October 22, 2025, 03:16:46 PM
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462 with TFS heads, about 10.3:1 SCR. Is there an appropriate gasket, .030-.041 thick compressed, block bore will be +.030, that minimizes gasket volume? How much larger than the block bore size does the gasket bore need to be? Thanks, Chuck (S)
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I built one like that with a cometic gasket not too long ago. I believe Cometic recommends.030 to .060 larger gasket bore, than block bore. I’ve seen plenty of instances slightly less than this. Cometic has plenty of variations to accommodate many combinations. I know they make a 4.165 gasket bore, and a 4.250 bore gasket. Anywhere between .027 and .120 in close increments. This is just one gasket option, not financial advice.
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Yes, .030" setback is generally the ideal minimum, except for "special" instances, and anything greater than .060" isn't aiding the gasket but does have other effects. :)
Scott.
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Couples of notes here:
1. You can get pretty close as long as the cylinders are on the same center as the gasket. I've ran a lot of 4.375" engines with 4.400" gaskets.
2. I would pick the head gasket last. Tolerances can stack up against you and even though you plan for (for example) a 1.325" compression height, 10.150" deck height, and a 6.700" rod with a 4.250" stroke, you can get a stray .001" here and there.
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I’ve been fighting with finding a gasket that I like lately… last set I ordered from cometic 4.165 bore gaskets and they were measured 4.200-4.320 depending what clock position you pulled the calipers across… just a FYI. Not sure why their gaskets aren’t concentric with the list a bore size. Only thing I can surmise is they are compensating for the old iron cylinder head chambers being wider at the valve centerline/pierce point than the bore size is. Just trying to save you the disappointment of spending good money on gaskets just to not get what you want. Good luck
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In an engine like the 462 above, changing a Felpro 1020 to a 4.20 bore only gains .084:1 compression, 10.315 to 10.399. Not sure I'd bother for the money.
However to answer the question, I have only done a couple at 4.375 and used a 4.40 Cometic and worked well. So I would not be afraid of a 4.160 engine, assuming a properly prepped flat surface and a Cometic with a 4.190 or larger bore.
Test fit if going close though, because every so often you get a weird one from Cometic, not common and I use them all the time, but have seen a couple that the bore was not centered
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My thanks to everyone who responded with helpful information. I have had mixed results from Cometic. Once no problem, the second purchase they needed 3 tries to get my custom speced gaskets right (Boss347). I am a bit surprised that they don't offer a 4.190- 4.200 bore gasket. I think I'll call them and ask if they have something in that size. Chuck (S)
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Chuck, CGT-C5834-023 and -040 I’ve tried advertised at 4.165 and weren’t round bore and measured kinda egg shaped in the 4.200-4.320 size range. I have some old Victor 3389 gaskets here that measure .038 thick and 4.300 bore or a 3417 Victor that measures 4.165 intake to exhaust direction and 4.220 water pump to flywheel direction, but they measure .048 thick. I really like the 3389 gasket for anything 428 bore and smaller. The last felpro race gaskets I measured were over or at .050 thick and 4.400ish bore. As always I never assume anything anymore and always measure everything at least twice. Good luck!
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Thanks Cody. Parts selection is proving to be a chore. Chuck (S)