horse power gain in compression
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horse power gain in compression

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    Default horse power gain in compression

    How much H P gain should you get in a 2.5 points in compression say like going from 10.5 to 13 to 1 rough estimate Thanks,

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    I think you also have to incorporate other things like camshaft and head flow to really maximize the gain. My guess is 60-75HP, as well it will bring good gains in torque, across the board as well.
    Last edited by Jspeeddemon; 10-30-2013 at 05:04 PM.

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    You can't give it an HP number with the info the OP gave.
    Just to start, is it a 285 SBC, or a 632 BBC? The gains for the 632 are going to be wee bit more than 50-75HP and for a 283 it would be over optimistic.

    You can go play here. I make no claims to its accuracy.
    Compression Ratio HP Determination Program



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    Last edited by gn7; 10-30-2013 at 05:24 PM.

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    Bob..Where do you find this stuff?

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    Quote Originally Posted by Gone Green View Post
    Bob..Where do you find this stuff?
    Stumble over a lot of it looking for other things, hitting links. Sometimes even at work researching a completely unrelated topic but something like that pops up, and I will save it. DEEEEP favorites files.



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    Quote Originally Posted by gn7 View Post
    You can't give it an HP number with the info the OP gave.
    Just to start, is it a 285 SBC, or a 632 BBC? The gains for the 632 are going to be wee bit more than 50-75HP and for a 283 it would be over optimistic.

    You can go play here. I make no claims to its accuracy.
    Compression Ratio HP Determination Program
    Thanks for the help I was building a 13 to 1 stroked 4.250 crank with a 4.375" bore.race gas engine, with dart pro 1 345's cleaned up a little, and a decent cam in the 700 hundreds I don't have the card in front of me and then I changed my mind, so I bought a dart block 4.5 bore to make me a 540" with .904 lifter bore 10.5 compression pump gas 93 octane am I loosing a bunch of H P or do the inches do me fine,?
    Last edited by litewing468; 10-30-2013 at 09:16 PM.

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    Quote Originally Posted by litewing468 View Post
    Thanks for the help I was building a 13 to 1 stroked 4.250 crank with a 4.375" bore.race gas engine, with dart pro 1 345's cleaned up a little, and a decent cam in the 700 hundreds I don't have the card in front of me and then I changed my mind, so I bought a dart block 4.5 bore to make me a 540" with .904 lifter bore 10.5 compression pump gas 93 octane an I loosing a bunch of H P or do the inches do me fine,?
    The heads and cam are important with a high compression build. With a pump gas build they are critical. Blow the specs on the camshaft on a pump gas deal and you won't get near the power of a 511 ci (30 inches smaller) with high compression.
    I will warn you up front, a cam you thought was bad ass for the high compression deal can be a power killer with pump gas compression. Too much duration, and a wide LSA with a late IC and the power flies out the door.



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    For every point of compression increase you gain 7% in HP based on the CID.

    Example. Engine CID is 454. 7% equals 31.78HP per 1 point gained.
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    Quote Originally Posted by litewing468 View Post
    How much H P gain should you get in a 2.5 points in compression say like going from 10.5 to 13 to 1 rough estimate Thanks,

    All else being equal assume 4-5% per point of compression.

    There is more to be gained going from 9:1 to 11:1 than there is from 11:1-13:1

    I'd assume that you'll gain an average of 4% on your 2.5 points. so on a 600hp engine 24hp on a 700hp engine 28hp

    Your results may vary but assume on the conservative side as it helps not being disappointed with results

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    Quote Originally Posted by Sleeper CP View Post
    All else being equal assume 4-5% per point of compression.

    There is more to be gained going from 9:1 to 11:1 than there is from 11:1-13:1

    I'd assume that you'll gain an average of 4% on your 2.5 points. so on a 600hp engine 24hp on a 700hp engine 28hp

    Your results may vary but assume on the conservative side as it helps not being disappointed with results
    By your statement, wouldn't that be 2.5 x 4%, so a 10 % total gain?

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    Default Wear and tear...

    Quote Originally Posted by litewing468 View Post
    Thanks for the help I was building a 13 to 1 stroked 4.250 crank with a 4.375" bore.race gas engine, with dart pro 1 345's cleaned up a little, and a decent cam in the 700 hundreds I don't have the card in front of me and then I changed my mind, so I bought a dart block 4.5 bore to make me a 540" with .904 lifter bore 10.5 compression pump gas 93 octane am I loosing a bunch of H P or do the inches do me fine,?
    IMO, you will be happier with the lower compression even though you will lose a few percentage points of HP. In the "long run" the lower compression will tear up fewer parts than the higher, (13:1) compression that puts a tremendous load on the bottom end... IMO, the higher the compression, the more required maintenance, and a shorter lifespan.... Higher compression beats the hell out of bearings, flexes crankshafts, distorts blocks, stresses rods, and usually leaves you fighting detonation for the life of the engine... Not to mention the price of race fuel these days.... All that said, if you're looking to squeeze every last ounce of horsepower out of a given cubic inch, go high and plan to keep spending money long after your project is "done"... If you're looking for that elusive idea of having FUN, use the K.I.S.S. principle... You'll be a lot happier with the results of using your boat, rather than telling all your friends how fast it WAS before it failed..
    Ball$ out, high compre$$ion engine$ require ball$ out very high quality part$...$peed cost$ money, how fa$t do you want to go??? Always remember, boating is suppose to be FUN..Good luck with whatever you decide to do.....Oh, and be SAFE...
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    Quote Originally Posted by Moneypit View Post
    IMO, you will be happier with the lower compression even though you will lose a few percentage points of HP. In the "long run" the lower compression will tear up fewer parts than the higher, (13:1) compression that puts a tremendous load on the bottom end... IMO, the higher the compression, the more required maintenance, and a shorter lifespan.... Higher compression beats the hell out of bearings, flexes crankshafts, distorts blocks, stresses rods, and usually leaves you fighting detonation for the life of the engine... Not to mention the price of race fuel these days.... All that said, if you're looking to squeeze every last ounce of horsepower out of a given cubic inch, go high and plan to keep spending money long after your project is "done"... If you're looking for that elusive idea of having FUN, use the K.I.S.S. principle... You'll be a lot happier with the results of using your boat, rather than telling all your friends how fast it WAS before it failed..
    Ball$ out, high compre$$ion engine$ require ball$ out very high quality part$...$peed cost$ money, how fa$t do you want to go??? Always remember, boating is suppose to be FUN..Good luck with whatever you decide to do.....Oh, and be SAFE...
    Ray
    Great post, and right on the money
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    Quote Originally Posted by Sleeper CP View Post
    All else being equal assume 4-5% per point of compression.

    There is more to be gained going from 9:1 to 11:1 than there is from 11:1-13:1

    I'd assume that you'll gain an average of 4% on your 2.5 points. so on a 600hp engine 24hp on a 700hp engine 28hp

    Your results may vary but assume on the conservative side as it helps not being disappointed with results
    There has to be a displacement factor in the equation.
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    Quote Originally Posted by steelcomp View Post
    There has to be a displacement factor in the equation.

    why ?


    Interesting article Popular Hotrodding did a few years back:

    Engine Compression Ratio - Tech - Popular Hot Rodding Magazine

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