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COMPESSION RATIO

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JD

02-18-2000 23:26:53




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DOES ANYONE HAVE ANY IDEA WHAT THE COMPRESION RATIO WOULD BE ON A 1951 JD A WITH ALUMINUM 45OVER PISTONS AND A HEISLER HEAD MATED TOGETHER




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Mike Aylward

02-19-2000 09:34:06




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 Re: COMPESSION RATIO in reply to JD , 02-18-2000 23:26:53  
JD, the PSI figure divided by 14 won't work for a number of reasons, including (but not limited to) atmospheric pressure, valve timing and lift, and compression losses (a poor-boy's way of saying volumetric efficiency). A stock gas A with cast iron pistons has 110 lbs. of compression pressure and a 5.6:1 compression ratio. I pull an A and a 60. An A with aluminum pistons will likely have about 6.2-6.5:1 compression, depending on style of piston. The Heisler head will probably add another 1/2-3/4 of a point of compression, but with more breathing. Your total will probably be around 7:1, with compression pressure in the neighborhood of approximately 150. This is an estimate, of course, but it is typical of what most A tractors I am familiar with run. My 60 runs close to 200 lbs. of compression pressure, and it has a compression ratio of somewhere in the neighborhood of 9.2:-1. Hope this helps. Mike

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DrCyKosis

02-19-2000 07:55:51




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 Re: COMPESSION RATIO in reply to JD , 02-18-2000 23:26:53  
JD no need to YELL at us we all hear fine.

CR is calculated by CCing the cylinder/piston/combustion chamber at TDC and BDC and using the displaced volume to calculate the CR using known gas laws. The calculations have to be done in absolute measurements (PSIA) then taken back to relative (PSIG) measurements to be at all acurate.

It gets pretty complicated to actually do so most people use the Kentucky windage method.

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al

02-19-2000 07:40:06




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 Re: COMPESSION RATIO in reply to JD , 02-18-2000 23:26:53  
Late A's and B's [gas] had 110 lbs comp.,and they were rated [memory]between 5and6:1.It sounds like you want to pull it,without knowing the exact volume at bottom diveded by volume at top you can't get exact.They say 200 is about 9-10:1,I asked how to convert a known ratio into an exact psi and was told by many it couldn't be done.

Al



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twopop

02-19-2000 06:29:14




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 Re: COMPESSION RATIO in reply to JD , 02-18-2000 23:26:53  
I DONT KNOW THE COMPRESSION RATIO BUT MOST TRACTOR ENGINES WERE FROM 6.5 TO 1 TO 8 TO 1 RATIO IF THE ENGINE IS IN GOOD SHAPE YOU CAN DO A COMPRESSION TEST AND DIVIDE THE RESULT BY 14 AND THAT CAN GIVE YOU AN IDEA OF WHAT THE RATIO IS ... 91 LBS OF COMP. DIVIDED BY 14 = 6.5 TO 1



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Gerald J.

02-19-2000 08:36:56




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 Re: Re: COMPESSION RATIO in reply to twopop, 02-19-2000 06:29:14  
Except that you don't know the cylinder pressure at the beginning of the compress stroke is 14 psi absolute. Likely it is significantly less because of intake manifold and carburetor flow restrictions.

Gerald J.



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