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Thoughts on using oval intake on rectangle heads

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Thoughts on using oval intake on rectangle heads

Old 09-05-2018, 01:35 PM
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Default Thoughts on using oval intake on rectangle heads

Long story short, 454 mag on roids build x2, 088 rectangle heads and I currently have edelbrock air gap dual plane intakes with oval ports laying around. I have read from multiple sources that the oval port intake may actually help velocity on rectangle heads?? Not trying to cut corners but this is at best going to be 500hp per side, not anything crazy. 2 new intakes at 350 each is 700 bucks that may not even make a difference in power at all. Thoughts?
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Old 09-05-2018, 02:30 PM
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I have heard some of the same things..I can say one way or the other as it would be best commented by someone whop has done dyno testing i would imagine...but....i have a motor right now that has a rec intake on oval heads! That's how i got it and it runs just fine.
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Old 09-05-2018, 02:32 PM
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No personal experience but have read that it works. I don’t think any big name builders would do it as a trick for more power, but I understand that the intake ports being a little larger than the head ports is a good thing with the little lip helping to create a touch of turbulence.
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Old 09-05-2018, 02:59 PM
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I thought for sure google would have produced a dyno test somewhere but I have not been able to track anything down. My bigger question than is it going to help, is it going to hurt me?
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Old 09-05-2018, 07:57 PM
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Buy a used rec port port online and and install one of each. If your boat goes out and does circles at wot then you'll be certain. Build depending can determinecas to wehether or not it would hurt you. I don't see you losing any noticeable losses. I played around with this years ago only the other way around on the water with real world numbers to show it. No difference in rpm or speed. Baja Rooster kinda explained it. Turbulence, tumbling may help fuel atomization which may in a sense offset the difference. Something I can't explain as to why however only give real results. Would I do it to gain on new builds? No.

You start getting into better flowing ported heads and it can really really take a turn to the worse in a hurry.
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Old 09-05-2018, 08:03 PM
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Many of the oval intakes sealing flange won't seal the rectangular heads ports. Off hand the one's Iknow will seal are the oval intakes that come with the smallblowers and also I believe the Dart Oval intake.

So,check this first.

Don't get too into the increased velocity thing too much with putting an oval intake on rect port heads on a 500hpengine. The proper intake would be a rectangular air gap for this style motor.
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Old 09-06-2018, 06:36 AM
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I also think sealing it may be a issue...now merc did the other on some factory stuff years ago with rec port intake on oval heads...could not believe that crap, only after saw the second one and talked to a few figured it was factory..
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Old 09-06-2018, 01:28 PM
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^^^^^^^ I believe Merc called it the "Performance Tuned" 7.4L/Bravo where they had the rectangle port intake/oval port heads.
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Old 09-06-2018, 01:49 PM
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I think in the long run you’ll be more happy selling what you’ve got and getting the correct ones. I searched high and low for a used oval rpm airgap and when they popped up they were snatched at $160 o pop. I still had to do a fair amount of hogging out to get the ports even close to being matched but doesn’t take too long with a drum rasp and wd40.
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Old 09-06-2018, 02:39 PM
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I cant see where miss matching parts ( ports ) will be anything but trouble, if Mercury did it they were probably using up excess inventory hoping to make it to the end of the warranty period, just my 2 cents.............btw I'll have two slightly used Vic Jr 4150 rec port intakes available @ the end of season
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