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Oval port or rectangular port intake???

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Old 10-09-2004, 08:47 PM
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Default Oval port or rectangular port intake???

I am putting together a 540 for next season. I have the short block done, the cylinder heads finally showed up from A.F.R. I am in the process of getting the correct valve springs and push rods. The next step will be the intake. I looking to run between 5000-5500 rpm. It should be making about 650-675 h.p. ( at least thats what my desktop dyno says)
I have talked to Dart and Brodix. They both seem to recommend their oval port manifold. I have heard of this trick some time ago, but don't know of anyone who has tried it, let alone someone with real dyno numbers to back up their claims. I understand the benefits of increasing the velocity of the intake by squeezing the intake runner down a bit with the oval ports. Also, I realize that at 5500 rpm , the oval manifold will still be able to flow enough to keep up with the demands of the motor. I know about the increase in torque that this would net. But do I really need it? I don't want to lose any top end power. After all, who cares how fast we can go at 3000 rpm, I want to get as much power as possible at 5500 rpm.
What bothers me is that it just doesn't seem right. With the motors I have built over the years, I have spent a large amount time making sure that the intake and head ports match up as perfectly as possible. Now, I am being told to drop a smaller intake port on these heads.
Does anyone have any experience with this? Any real dyno numbers??
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Old 10-09-2004, 08:56 PM
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Default Re: Oval port or rectangular port intake???

540 cu inches,you'll have plenty of torque,i'd want as much top end as possible,the band aid deal of running a oval port intake would probably be great on a small cubic inch engine but you'd sure hate to build a 540 that layed over at 4800 rpm's,Smitty
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Old 10-09-2004, 09:17 PM
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Default Re: Oval port or rectangular port intake???

That's my feeling also. BUT, Dart and Brodix are telling me that their oval port manifold will flow enough to keep up with my 540's relatively low rpm of 5500.
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Old 10-09-2004, 09:34 PM
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Default Re: Oval port or rectangular port intake???

I guess the only real answer to this (other than back to back dyno test with both manifolds)would be to look at it the flow #'s of both intakes. If you spend 2200-3000 on a set of afr heads that flow 320-400 cfm at .600 why would you want a intake that flows 280cfm ?You might as well have smaller heads if the intake flow doesn't keep up with actual head flow,but i don't know what a intake flows,anyone know?Smitty
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Old 10-09-2004, 10:21 PM
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Default Re: Oval port or rectangular port intake???

Dart and Merlin make Rec. ports too,,,why would they lie?? It's sort of like buying a cam,,,natural instinct is to go bigger but the Manufactuer usually can pick one better than us. Are your heads Rec. port? Even if, many times a smaller intake,even though mismatched will run better all around than a huge one. I think at 5500 you won't gain from a Rec intake but will lose in the mid-range(where we all run MOST of the time). But I REALLY think,,listen to the mfg Co. when they all agree
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Old 10-09-2004, 11:26 PM
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Default Re: Oval port or rectangular port intake???

Yes the heads are rectangular ports. They are AFR's 315 cnc'ed heads. I have to agree that the oval port intake will flow to 5000. I just would like to see some real numbers to back it up..
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Old 10-10-2004, 02:18 AM
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Default Re: Oval port or rectangular port intake???

That whole scenario makes me go hmmmmm, lot of valid points made above. But I would guess at higher rpm's the correct matching intake would work the best. Otherwise why would Dart make a matching intake to go with their heads if the other intake would work better. I definately believe at some point the smaller port oval intake with the square port heads would show an increase over the square intake/sq head combo but probably only at one point in the range say 3500. Guess it all boils down to being able to match all the pieces of the puzzle together correctly- Sq' port heads/intake/ and right cam and it should work better in the right app than a mixture.
 
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Old 10-10-2004, 05:47 AM
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Default Re: Oval port or rectangular port intake???

Arew you going to dyno your motors? If so I would try both so you know for sure. If you are not going to dyno then how about stelling ext boxes and dynos in them and them you can test to your hearts content and know for sure.
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Old 10-10-2004, 06:28 AM
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Default Re: Oval port or rectangular port intake???

Marty,
Yes I am going to dyno the motor. I understand that would be the best test. But, I was trying to get this combination correct the first time. I was hoping that someone here as done just what you have suggested.
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Old 10-10-2004, 09:12 AM
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Default Re: Oval port or rectangular port intake???

checkmate,

I may have the info you want. The past few years I have been running a pair of custom built 540's with some Dart 310cc Pro-1 bowl ported heads by JimV. I had a couple of Dart oval port single plane intakes that I wanted to get away with by trying to still use them on my 540's with the Dart rectangle port Pro-1's. JimV still had to grind open the port flanges of the oval port intakes a bit in order to match the ports of the heads. If I remember correctly it was the roof/top end of the port that needed the work, otherwise some of the air flow would have run into a wall up in that area. On the dyno with a 741 cam, 830cfm Holley and 8.2 comp ratio it made 630hp @5400rpm with 32* of timing.

The following year, I had JimV do a FULL PORT job on the Dart Pro-1's which opened up the intake port runner flanges of the heads a little more, but I did NOT need to have JimV do any further porting to open the intake manifold flanges up at that time---it was extremely close as it was anyway. We made a few other changes as well, 950cfm Holley, 8.7 comp ratio, 244*/244* cam, and on the dyno it made 699hp @5700rpm (that's all we ran it up to). Torque was at 704lbs @4800rpm. This was done on Tom Earhart's dyno which is within 2% of SAE standards. Even Merc has had him do some testing on some of their engines on Tom's dyno.

Keep in mind that the rectangle port on a Dart 310cc head is pretty small and the Dart intake seemed to have lined up well and pretty much matched up from side to side, but from top to bottom they were off and needed the top side of the port opened up to match the port of the head by about 3/16" or so. I am not sure if it would have made much of a difference, but that's what we did.

To bring you up to date, I now have a pair of 565 cubic inch engines with a pair of AFR 357 cnc ported heads that have an even larger rectangle port than the fully ported Darts heads did. The AFR ports are a little wider than the intake ports from side to side by about 1/8" or so (I think it ended up being that way all the way around the port), but I still have decided to leave the intake ports AS THEY ARE and just dyno test it that way. I wished I could have taken a picture for you and others to see, but we JUST bolted the intakes on last week and getting ready for the dyno.

In summary, my Dart oval port intakes were manufactured back around 1994 or so, therefore I am not sure if there have been any changes with them since then such as port shape or placement. I would think that with a small rectangle port such as the AFR 315 head that you would or may have to still do a little port matching if you were to use the Dart oval port intake with that particular head. However, as far as power goes the dyno tests show that the Dart oval port intake WITH the mods to the top of the port flange STILL made good power. We'll see how my 565's do with the 357 AFR cnc heads and those SAME Dart modified oval port intakes.

I wish you the best and I hope this helps you in your decision.

Mark/KAAMA

Last edited by KAAMA; 10-16-2004 at 08:14 AM. Reason: I made a small error in my wording
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