oval to rect. port manifold
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oval to rect. port manifold

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    Senior Member hotbo's Avatar
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    Default oval to rect. port manifold

    have there been any real advantages to putting rect. manifold to oval port heads.i know some who have done this but has anyone proven this is better??????or worse.like dyno proven??

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    I read somewhere that it doesn't affect HP output very much.

    I do know that if you do install a rect port intake on oval port heads that you have to use the rect port gaskets, otherwise you'll have water in the oil issue's and huge vacuum leaks which might make you take your engine to an engine guy which might cost you $1,100 to fix. Not that I have ever personally done that.

    I was also told by a racer that sometimes people will put oval port intakes on rect port heads to try and move the torque curve to where they want it to be at.

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    Senior Member hotbo's Avatar
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    thanks anyone else?????????is this been along time myth

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    Distinguished Member David 519's Avatar
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    I can't imagine a rec port intake on an oval port head doing anything except killing power. The upset in air flow at the transistion between the head/manifold would work like a restrictor. We spend a lot of time matching intake to the head so the transition is as smooth as possible.
    I can see going the other way; oval port manifold on square port head not being as bad. It would still be a significant impact on port velocity. As the flow goes from a smaller to larger volume, the velocity would drop...

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    Senior Member hotbo's Avatar
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    Quote Originally Posted by David 519 View Post
    I can't imagine a rec port intake on an oval port head doing anything except killing power. The upset in air flow at the transistion between the head/manifold would work like a restrictor. We spend a lot of time matching intake to the head so the transition is as smooth as possible.
    I can see going the other way; oval port manifold on square port head not being as bad. It would still be a significant impact on port velocity. As the flow goes from a smaller to larger volume, the velocity would drop...
    this has been along time trick of the trade for boat guys i know.they seem to think it will increase velocity puttin rec.on oval.me i want some damn proof.i have heard of others doing this as well.its fun to see that it cant be backed up as of yet,lol!!!!!


    come on fellas i know more than one of you have done or heard this or do you just not find it interesting

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    21 Daytona Outlaw's Avatar
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    I hate to admit it ...... but I have a rectangle port intake (Torker I think)
    on my 454 in my 68 El Camino. Just because I had it laying around when I installed
    the big block in it. I couldnt tell you if it ran any better or not because I never
    bothered swapping it out.

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    Senior Member hotbo's Avatar
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    well thanks for the post bro

    i know someone has a done this to prove it!!!

    please fellas

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    Quote Originally Posted by hotbo View Post
    have there been any real advantages to putting rect. manifold to oval port heads.i know some who have done this but has anyone proven this is better??????or worse.like dyno proven??
    Isn't that covered under the square peg in the round hole thing. you would think it would be OK to run an oval intake on a rec.port head but not a rec port intake on an oval headthat would kill your flow.

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    steelcomp was here
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    Quote Originally Posted by David 519 View Post
    I can't imagine a rec port intake on an oval port head doing anything except killing power. The upset in air flow at the transistion between the head/manifold would work like a restrictor. We spend a lot of time matching intake to the head so the transition is as smooth as possible.
    I can see going the other way; oval port manifold on square port head not being as bad. It would still be a significant impact on port velocity. As the flow goes from a smaller to larger volume, the velocity would drop...
    A good running big block with oval ports can definately use more air than most oval port intakes can provide. A step up to the rect. port intake can be very beneficial. More runner volume, and more plenum volume as well. The step at the port opening isn't as bad as you might think. There's really very little turbulence there, as the incoming air will pack against the intake surface of the head, and form a boundry layer of air that is relatively smooth. The transition becomes "well blended" with air. The benefits of the larger intake runners and plenum well outweigh the port mismatch. As far as port velocity, if the oval port intake is choking the port, then the velocity isn't an issue. The slightly lower velocity in the rect port intake again will be offset by the gains in the upper end power. My guess is there would be a gain across the rpm range, even at lower rpms, with a good dual plane like the RPM Air Gap or Stealth on even moderate performance builds. I know that just by throwing a 4V Ford 351Cleveland intake on a stock 2V engine was supposedly a 35hp gain. Someone who knows what they're doing can get a set of oval port GM heads to flow darn near as much as a set of rect ports.
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    Senior Member hotbo's Avatar
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    Quote Originally Posted by steelcomp View Post
    A good running big block with oval ports can definately use more air than most oval port intakes can provide. A step up to the rect. port intake can be very beneficial. More runner volume, and more plenum volume as well. The step at the port opening isn't as bad as you might think. There's really very little turbulence there, as the incoming air will pack against the intake surface of the head, and form a boundry layer of air that is relatively smooth. The transition becomes "well blended" with air. The benefits of the larger intake runners and plenum well outweigh the port mismatch. As far as port velocity, if the oval port intake is choking the port, then the velocity isn't an issue. The slightly lower velocity in the rect port intake again will be offset by the gains in the upper end power. My guess is there would be a gain across the rpm range, even at lower rpms, with a good dual plane like the RPM Air Gap or Stealth on even moderate performance builds. I know that just by throwing a 4V Ford 351Cleveland intake on a stock 2V engine was supposedly a 35hp gain. Someone who knows what they're doing can get a set of oval port GM heads to flow darn near as much as a set of rect ports.
    well once agin thanks steelcomp

    okay heres why im asking i have 781 big valve heads,i did the work on maybe not the best but the best i could do,lol!!!i have no flow benchi spent alot of time on my rpm air gap port matching 3 inches in working out.i have a new rect.rpm air gap im wanting to put on and try,but only if its gonna be a good thing b/c when i do this the oval is gonna go on a build im doing and cant switch back

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    steelcomp was here
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    Quote Originally Posted by hotbo View Post
    well once agin thanks steelcomp

    okay heres why im asking i have 781 big valve heads,i did the work on maybe not the best but the best i could do,lol!!!i have no flow benchi spent alot of time on my rpm air gap port matching 3 inches in working out.i have a new rect.rpm air gap im wanting to put on and try,but only if its gonna be a good thing b/c when i do this the oval is gonna go on a build im doing and cant switch back
    Before you commit the oval port RPM to another build, put the rect port on and try it. IMO, if something like that dosen't make a seat of the pants change, or at least an obvious gain in performance like MPH or rpm, then its usually not worth it. Port matching the oval port really dosen't get you anything, since it's the overall runner and plenum design (flow potential) that's lacking. The only way you'll really hop up the performance on the oval port intake is to fully port the runners. At that point you're into it way too many hours, and may as well bolt on the bigger intake, pot mismatch and all. If the bigger intake dosen't wow you, put the oval port back on and be done with it.
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    Senior Member hotbo's Avatar
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    well thats a problem b/c my engine job im doing has do be done before it warms up enough here to go boatingso it will be a gamble i guess at the very least its worth it from what you say???

    even if the intakes are the same the runner is longer on the rect.vs oval???huh?i just get tired of b.s. i personally dont have the money to take my engine to a dyno and test intakes so im a poor boy dyno,lol!!!! bolt it on read tach and buster loose.

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    Quote Originally Posted by hotbo View Post
    well thats a problem b/c my engine job im doing has do be done before it warms up enough here to go boatingso it will be a gamble i guess at the very least its worth it from what you say???

    even if the intakes are the same the runner is longer on the rect.vs oval???huh?i just get tired of b.s. i personally dont have the money to take my engine to a dyno and test intakes so im a poor boy dyno,lol!!!! bolt it on read tach and buster loose.
    There ya go. My hunch is that it'll be an improvement.
    If God is your co-pilot, change seats!
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    it'll work fine. the 468 that came in my tx had 781's with a rect victor and the throttle response was very nice, ran good at 6k.

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