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Tractor Pulling Discussion Forum

How much compression is too much?

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anothertractor

11-10-2004 05:03:09




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Hey yall, the tractor needs a little sprucing up this winter and I need to ask a questions about compression. Lets say that you have a 4 inch bore and 4 inch stroke, (824CC). If you have an 82.4 cc compression chamber, is this a 10:1 compression ratio? Also, how high should I try to get the compression? I am looking at getting some rods made to get the compression just right and I am not exactly sure how high I need to get the piston. Thanks for any help.

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anothertractor

11-12-2004 04:46:39




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 Re: How much compression is too much? in reply to anothertractor, 11-10-2004 05:03:09  
Thanks for everyone's help. I think I have a plan now.



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tony smithson

11-10-2004 17:20:56




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 Re: How much compression is too much? in reply to anothertractor, 11-10-2004 05:03:09  
just put in a 45 crank and the same pistons, cheaper than buying rods.



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buickanddeere

11-10-2004 18:24:21




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 Re: How much compression is too much? in reply to tony smithson, 11-10-2004 17:20:56  
Mechanical compression ratio or effective compression ratio? More cam duration requires more mechanical ratio to keep the same compression pressure.



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i believe

11-10-2004 18:27:19




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 Re: How much compression is too much? in reply to buickanddeere, 11-10-2004 18:24:21  
I believe how to figure C.R., you:

(Volume or one cyl.+combustion chamber cc's)/combustion chamber cc's..



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champspa

11-10-2004 15:49:10




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 Re: How much compression is too much? in reply to anothertractor, 11-10-2004 05:03:09  
your on the right track , just get it to 240psi cylinder pressure and that will be enough



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anothertractor

11-11-2004 10:45:54




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 Re: How much compression is too much? in reply to champspa, 11-10-2004 15:49:10  
I figured that I would need somewhere in the neighborhood of 240 PSI but I am not sure how to calculate what I need to do by PSI. Is therea direct relationship between PSI and compression ratio? (like 12:1). I need to know what would be a good desired ratio or a conversion for PSI to the ratio figure. Can anyone help with this?



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ChadS

11-13-2004 06:46:15




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 Re: How much compression is too much? in reply to anothertractor, 11-11-2004 10:45:54  
I was thinking about a scale on relitive compression pressure to the ratios, Here is what I came up with, it is just a guess, but I think is it real close.... Hope this helps,, ChadS



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pulller

11-11-2004 16:31:22




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 Re: How much compression is too much? in reply to anothertractor, 11-11-2004 10:45:54  
12:1 is just potential. its a relationship in total cubes and combustion chamber size. THe valve size and cam types/settings make a big differance in compression psi. 12:1 is way up there.....most small engine builders shoot for 9-11:1...and then your talking another point on a larger motor..... ..lots of stress.....some cars have up to 12.5:1, but never do get the compression figures up there right for the rpms they run....where a properly breathing tractor will be through the roof..... ..i would shoot for 9 or 10:1 compression ratio....

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FARMALL

11-10-2004 06:25:34




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 Re: How much compression is too much? in reply to anothertractor, 11-10-2004 05:03:09  
To figure compression ratio properly you must use this formula:
(Head volume + Piston to deck volume(+or-) + Gasket volume)= Squeeze volume
Take cylinder volume+ Squeeze volume divided by
squeeze volume or simply go to www.compression ratio computation. Hope this helps
Farmall



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