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Comp ratio

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Andy

12-25-2002 08:47:28




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let me ask all you engine building folks out there, If you were building a div 3 or 4 motor what would be the desiered comp ratio to aim for? Or is more info needed to determine that? like Cu In, RPM, Wt class,ect?




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Mark Murphy

12-26-2002 10:10:06




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 Re: comp ratio in reply to Andy, 12-25-2002 08:47:28  
I have scanned your web site periodically for many months. I would like information on how to build a pulling tractor for the Antique tractor puller. I have a Massey 44 (1951) with the 4-cycliner Continental. I have no clear way to procede. Any recommendations????



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Andy

12-25-2002 17:10:02




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 Re: comp ratio in reply to Andy, 12-25-2002 08:47:28  
I did not mention the # of cyl's but it would be 4 at 2000 rpm in my question. I am buliding a pulling engine and need to know what comp ratio to aim for.



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TimC

12-25-2002 20:20:53




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 Re: Re: comp ratio in reply to Andy, 12-25-2002 17:10:02  
Have a professional engine builder (disclaimer)
shoot for no less that 200 psi. I would stay under 300 if i wanted it to live for several seasons with little maintance.

This is only an opinion.



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G Taylor

12-25-2002 14:36:03




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 Re: comp ratio in reply to Andy, 12-25-2002 08:47:28  
Actaul ratio varies on air & metal temps, fuel,ignition lead, air/fuel mixture, spark plug placement and combustion chamber shape/size. More compression equals more HP all other factor identical UNTILL it detonates/pings/knocks. Then a 4 to 1 all fuel on kerosene will out pull a pinging x to 1 ratio on race gas. Beter too little than too much compression ratio.



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TimC

12-25-2002 13:16:40




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 Re: comp ratio in reply to Andy, 12-25-2002 08:47:28  
IMHO, any power needed to get the piston to TDC is gained back by the exact same cyl pressure on another cly wanting to push its way back down wheather it fires or not. Add to that the tremendous pressures generated during ignition and whala, hp/torque. On fuel engines the more pressure the more the power up until you cross the threshold of 17:1 according to test that General Motors did many years ago. This all provided the fuel does not pre-ignite.

When talking about very low RPM 2 cyl tractors then the geometry and physics may very well change, I don't know. I would want as much cyl pressure as the fuel would allow.

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JD Puller

12-25-2002 10:11:06




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 Re: comp ratio in reply to Andy, 12-25-2002 08:47:28  
My opionion is that about 8:1 is about enough becouse to much compression will hurt you more than it will help you. When you get to the end of your pull, and the engine is realy luging down the engine will not have enough momentom to pull the piston though the compression stroke. I have an unstyled A john Deere that is only about 8.3:1 compression and though the valve train, and carbration, I am getting about 75 horsepower. In fact I am still using the original Cast Iron pistons.

Hope this helps

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Bob C

12-25-2002 20:26:41




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 Re: Re: comp ratio in reply to JD Puller, 12-25-2002 10:11:06  
there is no such thing as luging with a good six cylinder oliver running around 260-285 lbs. comp. Just keep motorin till the wheels break free or the full-pull horn sounds



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Jack A

12-26-2002 06:14:48




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 Re: Re: Re: comp ratio in reply to Bob C, 12-25-2002 20:26:41  
Bob I thought 660's were a 4 cyl



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B.C

12-26-2002 15:08:59




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 Re: Re: Re: Re: comp ratio in reply to Jack A, 12-26-2002 06:14:48  
They are Jack, but settlin in at 1250-1300 RPM isent exactly lugging. Stay outa 5th gear and thats the range she will stay in. LOL But than i dont need to tell you that, do I LOL



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