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Thread: rect port bbc intake on oval port heads?naturally aspirated

  1. #1

    rect port bbc intake on oval port heads?naturally aspirated

    i have a friend that told me after dyno time on 2 different engines ,a square port intake was installed on both ,and both had oval port heads ,,,engines made 30 or so more hp at the same rpm,,,i know it should'nt matter on a blown motor cause i've done it ,,,but just seems impossible that it could make more hp with that kind of port mismatch,,,anyone ever heard of this ?
    i,m a doubting thomas !

  2. #2
    Senior Member RACING JUNKIE
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    I can't attest to the amount of hp gained, as i don't have any dyno data, ( as of yet i should say) but there are some that use this method, to gain hp.

  3. #3
    Senior Member RACING JUNKIE oldandtired's Avatar
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    On a carb motor, you can run a oval intake with square port heads (causes an anti reversion step). Will never work opposite.
    Blower motor - I just don't know but think you are losing efficiency.
    Dave
    http://www.racingjunk.com/profile/343797
    "All that is necessary for the triumph of evil is for good men to do nothing" Edmund Burke

  4. #4
    Senior Member DYNO OPERATOR
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    rect port

    Back in the early 70's, when there were alot of 396 oval port engines with cast iron intakes from the factory, we all pulled them off and put factory 375 horse rectangular port aluminum intakes on the 325 and 350 horsepower engines.

    I swear we thought they were faster even with the port mismatch. Maybe it was just losing the weight of the iron intake?

    I can also remember using the wrong intake gaskets the first time and having a hell of a big vacuum leak. Took a couple beers to figure that one out.

  5. #5
    Senior Member RACING JUNKIE
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    Hmmmm, If there was anything gained by "Port Mismatch" either way, do you suppose CNC matching would be the business it is today?

    I'll go with the matched ports everytime . . I might not be 100% right but 55 years of conventional wisdom tells me that I'm close . .

    Heheheheheheheheh . . .

    And I'd guess, on the Dyno Runs and during the changes, they did something else that offset their results . . Depending upon the total output, 30 HP could be 20% or 2% . .

  6. #6
    Senior Member RACING JUNKIE
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    There is et and hp when running a rect port intake on a oval head .. seen it more then once with the older gm heads.
    David Lanning
    IHRA NHRA 387B

    Fleenor Racing Transmission
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  7. #7
    Senior Member SENIOR BUILDER
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    I have done it myself, had a set of 781 GM ovals with a team g intake "oval", pulled engine out of car to put rear main seal in. Hoist hooked to carb pad and cracked about 1" under carb pad.......... Had a team g square port on the shelf with a set of gaskets, I wanted to go racing that coming weekend so I put it on. The car did pick up from 6.09 to 6.04. Cant swear the intake done it, but Im sure it wasent the rear main seal.
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  8. #8
    Senior Member MASTER BUILDER
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    That is/was a common deal on super stock engines. Its about velocity. It slows the air speed down, letting the engine go up in rpm, which, will make the car et better if its making more power at higher rpm.

    Super Stock engines are very velocity limited. Basicay, its telling you your heads are to fast. Its a crutch, and if you addressed the situation correctly, correct air speed in heads, it would run even faster.

    Frank


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