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??

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

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.

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

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 :)

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..

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.

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.

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.

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

Re: Oval port or rectangular port intake???
 

Mark,

Thanks for the great information. I was expecting to have to do some port matching whether I use the oval or rectangular intake.
As I said, both Dart and Brodix recommend using an oval intake. They say that at 5500 it will still flow enough to keep up with the heads and produce better power across the board. I am going to give Wilson manifolds a call tomorrow to get their input . I will be using their tapered spacer as well. I have heard of great results with this type of spacer. I have a friend who has tested several spacers on a dyno, he says the tapered Wilson is the best. I will post what they have to say about this.

http://www.wilsonmanifolds.com/

Re: Oval port or rectangular port intake???
 

I'm using Merlin rect. port intakes on my 540's with AFR 335's. It's my understanding that the Merlin runners have a smaller cross section than Dart or Brodix. The port match was very good. Probably less thana 1/16 off. I never dyno'd mine but board member RLW got 700 hp using a Merlin, AFR heads and a small Comp cam. While I've had problems with idle quality (too large of a cam), I've never had a problem getting on plane because of not enough torque.

Re: Oval port or rectangular port intake???
 

Patriyacht,

I thought you bought the 315 AFR cnc ported heads??? Are the 335's you have cnc ported? Glad to hear it's running well for you. What size cam are you running with your combination? What size of AFR heads and cam is your friend "RLW" running?

The cams I will be running are just some little fellers (duration at .050 is 232*/238* on 112* lobes .578" lift on both sides). The 357 cnc ported AFR's really flow well---especially the low lift flow numbers. I'm thinking the cam should really work well with the AFR's I have.

Re: Oval port or rectangular port intake???
 

Gentlemen,
I am running the AFR 305 "CNC'd Chamber" heads on My Dart Big M based 540.
My cam is a custom ground hydraulic roller CompCam.
Specs are as follows:
Intake/Exhaust
285/[email protected]"
236/[email protected]"
.630/.635 lift
112 LSA
I am not sure at what point the ICL is installed. Have to confirm that with my engine builder. Possibly at 112 degrees according to the Cam Card.

I am seeing 700 ft/lbs at 4900-5000 rpm. I feel this is too far up in the rpm range. Horsepower is 718 HP at 5900 rpm. Also too far up in the rpm range. I am now seeking solutions to get these rpm numbers lower at the cost of sacrificing HP and Torque.
I suggest a cam choice to get your HP down to 5400-5500 rpm and torque down in the low to mid 4000 rpm range. This will prevent torque loading the outdrive.
I am presently using a Merlin single plane intake with a Nickerson 1050.
I really don't want to get into a cam change but am seeking out alternatives.
This is installed in a 1989 27' Activator with XR/Imco 2" Shortie combo.
I suggest a call to RMbuilder for cam choice. He really knows his stuff and I wished I had known him prior to this build. Maybe he'll jump in on this thread.
Russ

Re: Oval port or rectangular port intake???
 

RLW,

I have installed an Isky hydraulic roller.
intake .578 lift 238* @.050
exhaust .608 lift 248*@ .050
114 lobe seperation
installed @ 111*

I also have a Dart Big "M" as a block , AFR 315 cnc heads, 9.25 compression. On my desktop dyno, the h.p. peaks @ 660 @ 5500 rpm, torque peaks 680 @ 4500 rpm.

Re: Oval port or rectangular port intake???
 

Checkmate540Bulldog :D ,
Can you run my numbers in your DeskTop Dyno?
My compression is the same at (9.25:1). I am curious of the outcome.
I like your numbers. I know this is an intake thread but it's all good stuff.
Russ

Re: Oval port or rectangular port intake???
 

RLW,
I would be glad to. I just need your valve timing #'s. My program doesn't work off of duration, it calculates off of the valve opening and closing points. IE: Intake valve opens @ xx* and closes @ xx*, exhuast opens @xx* and closes @ xx*.

Have your heads been modified since AFR did them? If they have been, I need the flow #'s, if not I have the original #'s from AFR.

Re: Oval port or rectangular port intake???
 

Kaama, The cam I used was the Crane 651 with 244 intake@ .050, 256 exhaust, .630 lift. It worked great in my old engines with Merlin heads. When I changed to the AFR's the whole personality of the engines changed. The heads flow so much more that the cam seemed larger. The idle quality went to hell and the exhaust reverted badly. I'm guessing that the power peak is in the 6000 rpm range, an rpm these engines will never see. I'm thinking of trying the cam RLW was using. However, he's thinking of going smaller... Going to the Pirates Ball this year?

Re: Oval port or rectangular port intake???
 

Actually you don't want the intake to line up with the head perfectly. You want the head to be above the floor of the intake about .100". A little step there to promote better "mixing".

Chris

Re: Oval port or rectangular port intake???
 

You will be very pleasantly surprised with the oval port intake. It will keep velocity high and carry a wider torque range as opposed to the narrow higher peaking torque of the rectangular port intake. If you're into racing then it would probably be better to run the rectangular port. I say probably only because I'm not convinced that the rectangular port even could stay with the oval port at peak horsepower in this 5500 RPM application.

Roby

Re: Oval port or rectangular port intake???
 

More good information gentlemen.

Checkmate,
I will get those numbers to you tonight via e-mail.
I am now wondering what an intake change would do to my engine's behavior. Not trying to hijack Checkmate's thread but this all seems to be related one way or another.
Russ

Re: Oval port or rectangular port intake???
 

Why do you think this? A step up on the way to the intake can really foul up the flow. The proper way to promote fuel atomization is to have a consistent texture from plenum to valve. I know your only talking about 3/32 but I don't see how this could benefit in any way.

Roby

Re: Oval port or rectangular port intake???
 

Roby,
By putting a "bump" in the floor, the laminer flow current will "toss" the fuel up and give better mixture which results in more power. Show's it on the dyno but not on a bench.

Chris

Re: Oval port or rectangular port intake???
 

But why not maintain a swirl texture on the intake & head port to keep the fuel suspended. I have always had the best results by finishing an intake port (intake and heads) semi-smooth then going over it with a rather coarse brake hone. My method for doing this was a clockwise push and a counter-clockwise pull on the front cylinder ports. and the opposite on the back cylinder ports. When I swore off carburetors I only finished the heads intake ports. However perfect port matching was essential.

Re: Oval port or rectangular port intake???
 

The Merlin rect port manifold is perfect for a 540 low RPM motor!!

Re: Oval port or rectangular port intake???
 

I don't know how rough you leave your stuff, I like nothing less then a 40 grit finish on the intake. Better yet the texture of a golf ball. People get into the the "tumble debate" which I don't know if you are pro or anti, but I can say this by leaving the step shows gains on the dyno. I feel it picks up the "stragglers" and gets them mixed in with the others.
I know Roby some of the cup teams have experiment with a " valve seat" area on the intake face of the head. This area is cut with multiple angles then blended with a flapper wheel. These angles protrude into the path of the intake runner.

Chris

Re: Oval port or rectangular port intake???
 

Absolutely, they are cut anywhere from 5 to 6 angles then blended. but they also use the swirling method on the port just as I described. I learned this many years ago from Stock Car magazine. I used to bolt my bare heads to the intake and go at it with the flexible hone. It really works. Now on my EFI engines I have done the texture of the intake manifold is fine at 200 to 250 grit extrude hone, and the intake port of the head is swirl textured.

Roby

Re: Oval port or rectangular port intake???
 

How low? I know the increased displacement size it will work better than a 454 but at 5500 RPM the oval port intake will hold it's own I bet

Roby

Re: Oval port or rectangular port intake???
 

You have to understand that a low rpm motor to Wette Vette is around 5900 rpm :D .

Re: Oval port or rectangular port intake???
 

I am not claiming to be an expert at porting. I am just going to report what my AFR cnc'ed ports look like. They have a numerous ridges or steps going down into the port both the intake and exhaust. I called them to ask why they left them like they, they said it was so the fuel / air mixture tumbles down the port. They claim it works well. I will try to post a picture later today.

Re: Oval port or rectangular port intake???
 

:D:D Okay now you really got my attention. Why would one want to "step" or texture the exhaust port?? I'm not ribbing you Checkmate, it just seems to me someone is BSing you. Stepping headers is one thing but the exhaust port??

Roby

Re: Oval port or rectangular port intake???
 

What do you think? This is how the heads came from AFR. It may be a little hard to see from just a picture, but there are little steps or ridges in the ports.

Re: Oval port or rectangular port intake???
 

Oh those? That's nothing what I was thinking as steps. Yes as you said those are to promote fuel suspension but I don't see why they're in the exhaust port.

Roby

Re: Oval port or rectangular port intake???
 

Those are the porting ridge marks from the CNC machine.

Re: Oval port or rectangular port intake???
 

I agree a single plane oval port manifold matched up to rect heads is a good option, but at 540 cubes and 5500 RPM the rect port Merlin is right at home. If we are talking 850 carb and considerably less than 5500 RPM the oval may do better. I imagine the cost of the oval manifold ported to rect heads will be more than the rect manifold for little to no gain.

RLW,
One thing to keep in mind with your combo is the dominator carb with efficient heads has allowed you to make very good average power over your cams operating range. It seems you have a relatively flat torque curve. This is a good thing and trying to move your curve down could create a peakier curve which in my .02 is not as good. The dominator carb may not be a benefit on your motor at 5400 RPM. Just prop accordingly and acceleration and top speed should be great. 5700 RPM is a good RPM for you to run and you will still have great durability.

Craig

Re: Oval port or rectangular port intake???
 

Those are just cutter marks from the cnc machining process. They may aid fuel suspension in the intakes they're not doing much in the exhaust.

Re: Oval port or rectangular port intake???
 

Thats what I was told from AFR. They did say that I should not smooth them out by hand and I should leave them alone.

Re: Oval port or rectangular port intake???
 

Intakes runners need to be rough.

Chris

Re: Oval port or rectangular port intake???
 

There is a very simple and accurate way to get wet flow inlet runner sizing for a given displacement and desired RPM at which to reach peak torque. Because torque is an independent variable and HP is a dependent (upon torque production) variable, you will most always focus on torque production in tuning. Peak torque occurs at or near the point of peak VE. Runner length, cross sectional area and plenum volume are the parameters used in intake selection. Runner cross sectional area is most responsible for the placement of where peak torque (and maximum volumetric efficiency) will occur. If you get peak torque where you want it (and keep the curve relatively flat for marine applications) the HP will take care of itself. These cross sectional areas will provide the correct flow velocity relative to displacement and rpm. To determine the correct cross sectional area of the inlet runner use this calculation.
Cross section area = (cylinder volume * peak torque rpm) /88200

Example for a 540 CID engine to make peak torque @ 4200 rpm
(67.5 * 4200)/88200 = 3.214 sq in intake runner cross section
Example for a 540 CID engine to make peak torque @ 5200 rpm
(67.5 * 5200)/88200 = 3.979 sq in intake runner cross section
Example for a 454 CID engine to make peak torque @ 4200 rpm
(56.75 * 4200)/ 88200 = 2.702 sq in intake runner cross section
Example for a 454 CID engine to make peak torque @ 5200 rpm
(56.75 * 5200)/ 88200 = 3.345 sq in intake runner cross section

You see there is a significant difference in the cross sectional requirements.
To build an engine that is not “peaky” for marine applications you want to keep max torque approx @ 75% of the rpm level of peak HP. There are other factors at work to determine the overall optimization. Cam selection, valve timing & size (relative to mean piston speed, max piston velocity, and piston acceleration) cylinder head flow, and exhaust designs. Good heads require less duration and as a rule of thumb durations in excess 236* don’t make more torque, they just raise the rpm torque is produced. That may raise your max HP output past the point of being able to utilize it effectively.
Bob

Re: Oval port or rectangular port intake???
 

Bob,
Always batting "Clean Up". Thanks Bob.

Chris
PS, Kaama want's to talk to you about Morel lifters.