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Compression Ratio

CID PSI Compression

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BIG JOHN

04-15-2002 18:50:11

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I see it all the time where someone wants to know how much compression they should have in their various tractors. Most all of the manuals have the Compression Ratio (for an H - 5.9:1) and the Cubic Inch Displacement (again for an H - 152.1)but rarely is the Pounds per Square Inch given.

I see talk about a formula to figure the PSI using the Compression Ratio and the Cubic Inch Displacement.

Could someone please post this formula and give some examples.

THANKS FOR THE HELP

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Theman

04-16-2002 05:55:00

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Re: Compression Ratio - CID PSI Compression in reply to BIG JOHN, 04-15-2002 18:50:11

Below is a link to a page that actually does the calculations for you. Scroll down to the engine calculation section and pick 'compression ratio'. Granted, it has it's basis in drag racing but if you really want to run good numbers on your engine, this is a good place to go. I used them when blueprinting the engine on my H.

Prestage.com

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justin

04-15-2002 20:05:50

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Re: Compression Ratio - CID PSI Compression in reply to BIG JOHN, 04-15-2002 18:50:11

I have set up a webpage that gives all this info by model of tractor look at the following webpage

IH Tractor Tune Up Info

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Bob M

04-15-2002 19:16:41

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Re: Compression Ratio - CID PSI Compression in reply to BIG JOHN, 04-15-2002 18:50:11

Big John - A simplified formula to calculate compression PSI from compression ratio is

(Comp Ratio - 1.0) x 14.7 = PSI

Example: If the compression ratio is stated to be 5.9:1, the the compression pressure should be -

(5.9 - 1.0) x 14.7 = 4.9 x 14.7 = 72 PSI

In actuality, compression pressure varies on altitude, barometric pressure, temperature and other factors. But near sea level, the above equation will be pretty close.

Note: Compression ratio is independent of cylinder displacement. Consequently displacement is not required to calculate compression pressure. However compression ratio can be very precisely calculated if you know the swept volume (piston displacement) and clearance volume (combustion chamber volume at TDC) for one cylinder.

Hope this answers your question...

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