| Farmall & IHC Tractors Discussion Forum |
Topic: farmall sm
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| tom thorn
09-25-2012 15:34:25
50.49.224.246
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what should the compresion be on a super m with a 450 gas head 4 1/4 bore
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| mkirsch
09-26-2012 06:02:48
64.80.110.74
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Re: farmall sm in reply to tom thorn, 09-25-2012 15:34:25
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| Compression in PSI as in a compression check, or compression RATIO?
In PSI, more is better and consistent across all cylinders is more desirable than a high compression.
IIRC you need 90PSI for an engine to run decent.
>100PSI is an engine with a lot of life left in it.
>125PSI is a good strong engine.
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| mike1972chev
09-26-2012 03:49:35
75.149.81.173
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Re: farmall sm in reply to tom thorn, 09-25-2012 15:34:25
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| Like has been posted already. MANY factors affect compression.(Combustion chamber CC,piston dome/dish,cam timing,cam profile,ect.) Probably MORE important is that all cylinder PSI readings are within a small percentage of each other.
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| Super-H-Mike
09-26-2012 08:46:51
76.164.144.30
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Re: farmall sm in reply to mike1972chev, 09-26-2012 03:49:35
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| That is true Mike72. On an old tractor engine a psi that is close to even on each cylinder is a good indicator of how healthy the engine is. But, the higher the cranking compression the more likely the engine will be powerful, which is what I think he is after. In automotive, a 350 Chevy will run fine with 90 psi even compression, but if you want a motor that builds big power you will want that number much higher. Cam timing and profile can change things drastically as you stated. I have a snortin 454 BBC here that has 185 psi cranking.
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| mike1972chev
09-26-2012 10:53:20
75.149.81.173
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Re: farmall sm in reply to Super-H-Mike, 09-26-2012 08:46:51
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|  Me too. ;)
Thread is now "high jacked" lol
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| Super-H-Mike
09-26-2012 11:47:09
76.164.144.30
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Re: farmall sm in reply to mike1972chev, 09-26-2012 10:53:20
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| Yowza ! Put that in an SM, lol
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| robgIN
09-25-2012 17:01:56
76.208.51.131
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Re: farmall sm in reply to tom thorn, 09-25-2012 15:34:25
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| unless you are running without sleeves you won't have a 4.25" bore, stock was 4.00, most are rebuilt with the overbore kit to 4.125". If you are looking for a psi that will depend on piston design, bore dia and combustion chamber cc. Put a compression guage on it and see what you have .
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| dblair
09-25-2012 16:12:08
67.172.201.147
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Re: farmall sm in reply to tom thorn, 09-25-2012 15:34:25
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| 298 cu in , 7.18 to 1 compression with flat top pistons .
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