Re: Heads and compression

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Posted by John W. S. [] on Wednesday, June 12, 2024 at 01:17:27 :

In Reply to: Heads and compression posted by Daniel Saucy [] on Tuesday, June 11, 2024 at 17:18:54 :

The only surefire way to know what you have is to measure the combustion chamber with a compressed head gasket and calculate the ratio. All of these engines are likely to have been worked on at some point in their 60+ year life and there is no telling what, if anything may have been done. Also, some heads are super low compression; were talking 6:1 or less on some "export" parts. At 8:1 you are pretty safe but getting too carried away, upwards of 9:1 will significantly shorten your head gasket life. It seems common to see people cutting 0.050 - 0.070 without any valve clearance issues. I have a head that was cut to 8:1 and when I asked how much it took the answer was "a whole bunch". it has not been installed, but it looks very different than when we started.

I have not seen a 25" head with drastically different shaped chambers either. They seem to just vary in depth, unlike the 23" heads that have multiple designs.

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