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Thread: compression ratio calculator, (here!!!)

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    compression ratio calculator, (here!!!)

    having just picked up my new head I wanted to do some calculations for the compression ratio. its a 2ltr pinto

    I tried doing it long had on a bit of paper but went massively wrong, would one of the resident experts on this confirm if this online calculator is correct.

    https://www.rbracing-rsr.com/compstaticcalc.html

    these are my numbers and my answer

    bore 90.07mm or 3.570866'
    stroke 76.2mm or 3.0'
    felpro gasket 1.0mm or 0.0394
    distance from top of piston at tdc to deck is, 0.381mm or 0.015'
    my head cc'd at 44cc

    all that said I got a ratio of = 10.4 does this sound right???

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    Re: compression ratio calculator, (here!!!)

    also I have a HT1E cam shaft, after looking round I need to be up around 11.5?

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    Re: compression ratio calculator, (here!!!)

    it looks like your bore size is wrong, a std pinto is 90.8mm if fact so is your stoke, standard measurement is 76.95mm

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    Re: compression ratio calculator, (here!!!)

    Quote Originally Posted by Graham View Post
    it looks like your bore size is wrong, a std pinto is 90.8mm if fact so is your stoke, standard measurement is 76.95mm
    Yea I thought that when I started going through it with the info I learned about my engine 6 months ago. Though my pistons are 93.5mm.

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    Re: compression ratio calculator, (here!!!)

    The first thing your above figures don't look right if it's a Pinto on std bore and stroke, it would make your engine 1941cc.

    Assuming you have std bore of 90.80 and a std stroke of 76.90mm I work your compression out to be 10.40.1 using my method of calculations.

    In my opinion you need at least 11 50.1 as an absolute minimum to work with either of the HT cams.

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    Re: compression ratio calculator, (here!!!)

    The first thing your above figures don't look right if it's a Pinto on std bore and stroke, it would make your engine 1941cc.

    Assuming you have std bore of 90.80 and a std stroke of 76.90mm I work your compression out to be 10.40.1 using my method of calculations.

    In my opinion you need at least 11 50.1 as an absolute minimum to work with either of the HT cams.

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    Re: compression ratio calculator, (here!!!)

    Quote Originally Posted by Forest_rallying View Post
    The first thing your above figures don't look right if it's a Pinto on std bore and stroke, it would make your engine 1941cc.

    Yea I came up with that when I started adding it up an then just thought well if that bits wrong what else is...

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    Re: compression ratio calculator, (here!!!)

    either of the HT cams id be looking to run no less than 12:1

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    Re: compression ratio calculator, (here!!!)

    I calculated the bore at 90.7 not 90.07 that was a typo according to the paper I have it all wrote down on,

    Having done it again, with the bore / stroke numbers given above and got 10.28:1

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    Re: compression ratio calculator, (here!!!)

    I calculated the bore at 90.7 not 90.07 that was a typo according to the paper I have it all wrote down on,

    Having done it again, with the bore / stroke numbers given above and got 10.28:1

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    Re: compression ratio calculator, (here!!!)

    How accurately have you cc'd the combustion chambers?

    Unless you r'e going for forged pistons and higher compression I would be inclined to look for a softer cam.

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    Re: compression ratio calculator, (here!!!)

    Quote Originally Posted by Warrior View Post
    I calculated the bore at 90.7 not 90.07 that was a typo according to the paper I have it all wrote down on,

    Having done it again, with the bore / stroke numbers given above and got 10.28:1
    ok, but even so you have used a bore size smaller than std! presumably you have oversize pistons? first oversize is usually 91.3

    far too low for the cam you are going to run, you probably be missing 20 odd bhp from the top end and the bottom end power will be cack too

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    Re: compression ratio calculator, (here!!!)

    Correct is 90,84mm Bore and 76,95mm Stroke is 1994cc The first oversize Piston ford has delieverd was 90,95mm for Motorsport Engines. This is 1999cc.

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    Re: compression ratio calculator, (here!!!)

    What did you enter for piston top volume?

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    Re: compression ratio calculator, (here!!!)

    Quote Originally Posted by Escort TC View Post
    Correct is 90,84mm Bore and 76,95mm Stroke is 1994cc The first oversize Piston ford has delieverd was 90,95mm for Motorsport Engines. This is 1999cc.
    I remember buying a brand new GP1 short motor in 1984 and it had Mahle pistons fitted that were 90.95 mm and slightly thicker conrods. What a bargain that turned out to be.

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