step head pistons in an M

minnemoman · Oct 22, 2011

does anny body know the compresion ratio when the 4" step hed pistons are used, can you still run 87 or do you have to step up to the 91.

just thinking about putting some in my M when i overhall it next spring

thank you all for your time

CNKS · Oct 22, 2011

I don't know the compression ratio, but it was so low to begin with that a considerable amount would have to be shaved off the head, or maybe a head from a later LPG tractor would have to be used to require more than 87. So, 87 is ok. However, it may (or may not) be preferable reduce the timing advance. Dave Slater or someone else can clarify that. My thinking is that most overhauled M and Super M's already have step heads in them.

randy hall · Oct 22, 2011

depending on the brand of pistons the compression would be 6.4 to 6.8 to 1. m+w made some with one inch talldomes for lp use that made 8.0 to 1 with gasoline head [would still work with 87 octane] or with low compression head to bring the compression up. original gasoline compression was 6.0 to 1.

step head pistons in an M

minnemoman

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CNKS

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randy hall

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