boring over displacement
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500, 472, 425, 368 Discussion, boring over displacement in Cadillac Engine Technical Discussion; im going to need to bore my engine over. does anyone have a suggestion? .020 .030 .040 .060? any one ...
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    boring over displacement

    im going to need to bore my engine over. does anyone have a suggestion? .020 .030 .040 .060? any one better than another? my first instinct it .060 because its the biggest, haha. does anyone know what these different bores would increase the ci to? thanks

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    Re: boring over displacement

    Usually I'd say bore the engine out to the smallest bore that you can get away with. If you can end up with a good cyl wall with .020 over, do .020 over. That way in 100k miles if you need to bore it again you can. If you're going for a big bore engine you can go with .120 over or so without any block fill and technically up to about .2 to .3 over with fill, but that's a bit over the top for your motor probably.

    To figure out the displacement, use this equation, it will get you close enough:
    CID = 8 (the number of cyls) x bore^2 (squared) x stroke x .7854
    CID = 8 x 4.3^2 (stock bore) x 4.303 x .7854 = 500ci
    CID = 8 x 4.32^2 (new bore .020 over) x 4.303 x .7854 = 504.5ci

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    Re: boring over displacement

    Quote Originally Posted by Adumb
    im going to need to bore my engine over. does anyone have a suggestion? .020 .030 .040 .060? any one better than another? my first instinct it .060 because its the biggest, haha. does anyone know what these different bores would increase the ci to? thanks
    It may come down to what pistons are available. Smaller is actually better. It gives you more options in the future if you need to bore it again. Plus on some engines the bigger bore thins out the cylinder walls such that the combustion chamber heat begins to heat up the coolant a lot more.

    When I had my GN rebuilt there was a shortage of .030 pistons so I had to go .040 over, which on the 3.8L block is the max. If I need to rebuild it again I may have to get another bock. Also, the car runs considerably hotter - I had to put a bigger radiator and bigger fans in it. I'm not sure if the Caddy blocks have this issue tho.

    Jim

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    Re: boring over displacement

    davesdeville,

    Can you work one for me? (boring the 500 .030 over). I just don't understand the equation and can't get it to come out as anything near 500. Boy do I feel stupid!

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    Re: boring over displacement

    yeah,i agree with terrible one. i am not terrific at math. what is "^"? thanks.

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    Re: boring over displacement

    Quote Originally Posted by Adumb
    yeah,i agree with terrible one. i am not terrific at math. what is "^"? thanks.
    The "^" is "to the power of" or in this case 'squared'.

    Jim

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    Re: boring over displacement

    I just want to know how many cubic inches I will end up with

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    Re: boring over displacement

    .020 = 505
    .030 = 507
    .040 = 509
    .060 = 514

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    Re: boring over displacement

    Thanks

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    Re: boring over displacement

    so, if i bored .020 over i would have a 476, right?
    i think i did the equation right.

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    Re: boring over displacement

    sounds correct

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    Re: boring over displacement

    i did all the math so i figured id share so you guys dont have to. here it goes.
    472
    .020 = 476
    .030 = 478.2
    .040 = 480.4
    .060 = 484.9

    and im fairly sure my math is right. thanks for the equation dave.

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    Re: boring over displacement

    Thank Google.

    And come on guys, I got a D in Algebra I, and a D- (actually an F, but I went to class 4 extra days and did extra work for a D-) in Algebra II, but I still got that equation.

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    Re: boring over displacement

    well, i havent taken a math class in 2 1/2 years so everything i learned is basically gone, haha

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    Re: boring over displacement

    I suck at math. That's okay though because nice people one the forums can work out my displacement equations.

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