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Tractor Pulling Discussion Forum

Compression Ratio??

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Jason

11-29-2003 14:50:00




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Pardon my ignorance,but could someone tell me the definition of Compression ratio? What is it and how can you figure out the compression ratio of a engine. Thank you very much!




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TimC

11-30-2003 18:49:02




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 Re: Compression Ratio?? in reply to Jason, 11-29-2003 14:50:00  
Bore X Bore X Stroke X .7854 = swept volume.

Figure Cubic inches of the combustion chamber including valve releif, top land allowance, deck clearance and head gasket thickness. This is the compressed volume. Add the compressed volume to the swept volume for a total volume. Divide the compressed volume into the total volume for the compression ratio.

Usually combustion chambers are figured in CCs.
Do a search on yahoo or google for Online Compression Ratio Calculators to make things easier figuring.

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phil

11-30-2003 12:25:48




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 Re: Compression Ratio?? in reply to Jason, 11-29-2003 14:50:00  
It is the ratio of the volume in the cylinder when the piston is down compared to the volume in the cylinder when the piston is all the way up. Say that you could get a quart of water into the cylinder when the piston is down. And say that when the piston is 'up' you can get 4 ounces of water in the chamber above the piston. The compression ratio is 8 to 1, usually written 8:1.



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a puller

11-30-2003 10:41:35




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 Re: Compression Ratio?? in reply to Jason, 11-29-2003 14:50:00  
i don't know what the ratio is, but the compression can be put into psi of the cylinder. maybe the ratio is like 14psi an inch or something?? It'll be interestin to find out if anyone replys..lol



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JDGnut

11-30-2003 18:15:13




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 Re: Re: Compression Ratio?? in reply to a puller, 11-30-2003 10:41:35  
The ratio is as Phil descriped.. A puller is talking about Cranking Pressure... Cranking pressure can be related to compression ratio... but not an exact corilation... the cranking pressure is going to tell you how much pressure is being created... will tell you how good your valves are sealing, rings.. head gasket... Good Luck...
JDGnut



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