aluminum D vs. round port heads
 

I see a lot of posts from guys running aluminum D-port heads. I get the reasoning behind this if a guy already has iron D ports and wants to use his existing headers with a nice upgrade to aluminum heads.

Here is my question - if you don't have D port headers already and they make a round port header for your chassis ... why not just go with aftermarket round port heads? Other than header availability, do aftermarket D port heads have any advantage at all over aftermarket round port heads?

I recently had to deal with this exact dilemma on a personal car. Had already bought round port E-heads for my Catalina. But the log jam was the damn exhaust manifolds. Especially with a street Pontiac, with the great manifolds they had, why deal with the continuous aggravation of tube headers on the street? The endless exhaust leaks at the flanges, rusting out every 3 years, maybe 6 years if coated, extra noise, heat, fitment issues, poor ground clearance and so forth. But the problem is, the round port exhaust manifolds are made of unobtanium. After waiting nearly 2 years I finally gave up, sold the heads and bought a set of D-port Edelbrock heads instead. They do not flow as well, especially over .300 lift, but at least ram air and long branch manifolds are available. D-port heads are more difficult to improve the exhaust port, and probably cost me 20-25 HP. But at least I can drive my car.

If I was going to run tube headers, I would certainly use round port heads.

Another part to this that seems to not be considered is if the lesser port volumes ( area ) of the D port heads work better for your particular cid and the way it’s Cam’ed and geared.

Unless the motor is set up for full race and it’s narrow rpm band then it’s the average Tq and HP numbers that matter most .

i have edelbrock d ports and edelbrock round ports. although i think d port header avail is better still you can get round port headers for alot of cars now. i kinda bastard child my edelbrock dports just because i never liked trying to install 64/7 gto headers on d port heads. for whatever reason, i can install round port headers awhole lot easier. its hard to believe that 330cfm can be got out of the dports but butler has a program for it same as round ports, although round ports can go further,

At the very least, I like the wider bolt spacing on the center ports on round ports.

And, how many pontiac factory round port engines run worse than the d port counterpart? Even the RA2 with it`s d port type intake port is one of pontiac`s best runners.

I know we are talking aftermarket heads, but...

I was starting from a bare block and never considered D ports. My rounds perform great in my street car and it runs like a raped ape…finally.

D ports allow you to run the stock stove choke

Are there any downsides to running round ports on the street? Assume headers and a street/strip engine of 400-462 CID. 290 CFM intake port and HR cam in the 231-245 range on pump gas.

What's the decision tree when going from 260CFM iron heads, to either KRE/Edelbrock D-ports or Edelbrock/SM round ports? At what HP or RPM or application, does the D-port exhaust become a limiting factor?

D-ports will never make power of a round port. My headers are coated and are 28 years old, never rusted. The flanges are separated never any header leaks. D-ports are ok, if you want to use stock manifolds for a nice street cruiser.

I prefer the round ports but there are a few things that might dictate a Dport in certain situations as already mentioned.

Headers are not a big deal to me so that's not even factored in the decision making. Round ports are certainly much easier in that regard anyway and I've run headers for decades on many cars, including daily drivers without a single issue using them.

The choice would really just depend on what I'm trying to do with the car.

Just seems like people doing new builds are always going with the D ports and I don't really understand why! I have 87 cc round port edelbrocks with the old chamber style in a 505 with old faithful and a performer RPM, I can't imagine anyone driving my car and thinking, "ya know, this thing just needs smaller intake ports so it has more low-end" ...

My guess is probably cost being the biggest player lol

And that whole "more low end" myth is funny, amazes me that still floats around the internet but whatayado.

I mean hey, if I had some really nice headers and was upgrading from iron d-ports to aluminum heads, I don't see spending the extra cost for new headers if you are talking about a 550 hp build, something you can drink and drive daily.

But if you don't have headers already and new round port heads cost about the same as new d port heads ....

the cost cant be it, the d ports are more money, i think a few hundred more than even the cnc round ports.

i only bought d ports because my kids car was already running with 6x4s and we was gonna upgrade what he had. but i will say the edelbrock dport is a nice looking head much nicer than my 72cc old style heads i originally bought

Factory iron D ports can be ported to go 290 intake cfm at less then 190 CCs , so why is it so hard to believe that aftermarket aluminum D ports can go 330 when they start off at atleast 188 CCs if not 200?

i thought 260 270 was kinda reaching the limits of an iron d port.

Like has been mentioned. Most Pontiac heads came in D-port. It's what we all were use too. Folks would always have had d-port manifolds or headers. Having said that, A lot of folks would have just upgraded to D-Port Aluminum heads if available. There's a reason Kaufman came out with a D-port aluminum Head. and now Edelbrock came out with a D-Port head. You can build a nice 600 h/P street engine with d-ports.

From what I've seen CNC Dports from Kauffman to go about 325 cfm are about $3200. CNC eddy round ports from Butler at the same 325 cfm are $3700.

So yeah there is a price difference but that's not where the extra costs stop. There are exhaust differences to consider and when people already have a dport car with d port manifolds they are reluctant to spend the extra money for the change. Now you're looking at RA manifolds or headers that have to be swapped and that doesn't always line up with your existing exhaust system either so there are some cost modifications there to consider.

Steve C asked me to post this as he is currently unable.

here ya go, compliments of Steve........

https://www.motortrend.com/how-to/in...head-edelbrock

I wasn’t going to get into this, but I just can’t let this statement go. Maybe on your flow bench. LOL

A lot of emphasis on flow numbers, which dose mean something but not a hell of allot. What it really boils down to when it comes to a d-port vs round port is what your goal and what your intentions are with a Car.

Yeah maybe can get 290 cfm on iron d-Port, but whats the air speed in the port. Just a little example a set of wide ports done by well known Pontiac engine builder when checked ( because he was very disappointed) in the performance was you ready 425 fps. Finally after going to a guy Who has one of the best reputations, he ended up dropping it to 325 fps. Car pick up a tremendous amount of power. There’s allot more it then air speed in port. But just goes to show how much flow number only matter if its a good port.

Oh yeah of course when he drop the air speed the flow numbers drop also, but he pick up 75 hp.

Bottom line when I see flow numbers posted I cringe. Because it doesn’t tell you anything about the port. A d-port whether it’s an ion D-port or aluminum d-port has its limitations. Yeah we can boast all we want about the flow numbers oh they flow 320 cfm.

Here’s a 290 cfm iron #13 head with a 2.14” valve .
But, yes if you do not know how to check for core shift and take certain measurements then your far safer at 260 to 270 cfm. Plus it takes a lot less porting finesse then 290 cfm.

Well your going to have to let it go Lou because right now I have a a set of Ford Boss 302 heads that flow 288@28” and a BBC factory rectangular port Aluminum heads flowing 297@28”, and the head the I posted pictures of is right there with them.

If you where here I would be glad to slap all 3 on the bench within 30 minutes time of each other and show you.

Most folks I see on here with there street cars with ported aftermarket round port heads are way under utilizing them.
Either there not running enough lift and or duration.

Enough cid .

Or as a sub group of not enough cid, not enough rpm.

Most folks I see on here with there street cars with ported aftermarket round port heads are way under utilizing them.
Either there not running enough lift and or duration.

Enough cid .

Or as a sub group of not enough cid, not enough rpm.

Gach,
Are the air speed numbers you are quoting average port speed or a measured localize air speed?

Stan

I had a set of '69 #16 d-ports race ported years ago by Jerry Goodale and when tested on my engine builders bench at the time they flowed 291 at .600 lift (28").
Intake valves were 2.125".

Looking back I suspect that number could be a bit generous. A few years ago I sold the heads to Paul Knippen, on his bench they were 278-282 cfm at .600".
(he tested 8 ports)

However different flow benches, and the type of bench, and with different operators you can and do get different numbers. Sometimes all over the map !

.

You have to drive it for the headers to rust.

When CV-1 where first introduced, it was established that they flowed 380 cfm out of the box. Which by all means out flowed a wide port head. Pontiac Dude was doing a pump gas builded. Long story short he ran a 10.20 maybe even 10.10.

I went with Wide Port. Both same size motor. Trust me we went back and forth on this. He hong up on me a few times..and I on him…LOL My second pass with wide ports I went 9.80. I had a set of CV-1’s. But went with wide ports. His thing was he kept saying these heads flow 380 cfm. My wide ports only flowed 362 cfm. But at 750 lift.

Finally when he got his CV-1’s to Gabby..Gabby calls me, he says yeah they flow 380 cfm, BUT! The air speed in the port is only 252… so to make up for low air speed he’s going to need a minimum of 275-285 duration. My cam is or was 265/276 hey it was a learning process for both of us, but I already new what air speed was. When Dude would shift that thing into second gear the rpms would drop almost 1000 rpms. Its like the motor wouldn’t recover.

Of crouse theres allot more to it then just air speed in the port.

I was wondering how long it was going to take you…The trolls are out..Stan your next..lOL oh wait Stan beat you to it. Next !!

:pound: :pound:

Stan

Tolling Stan:horn:

Its funny you two make way to obvious.

OK, so Larry Meaux owns a flow bench and ports cylinder heads, he owns a dyno and builds engines. He also writes computer software (PipeMax) This is from his software.

Everybody has their own opinion. David Vizard who I authored a flow bench software program with likes to see around 300 fps.

Stan

So is it just CFM? When you need more than 260CFM from the exhaust port, (80% of 330CFM intake) you go round port exhaust? Is the chamber any different between a edelbrock round port and the Eddy D-port? Is one chamber better than the other?

How much can a D-port exhaust port realistically flow?

If you had a D port and a round port that had similar flow numbers and port velocities, would they make similar power?

Tom S. and I had this discussion years ago. I do believe Tom has more hands on experience running street engines with round port heads than anyone else here. When the man tells me to run long branch exhaust manifolds on a street engine I listen. If you really think you need extra exhaust flow you can always have the exhaust manifolds extrude honed. Mike, I agree: if you are going to run headers ( we have the problem of simply finding someone to fab headers for a ‘61-‘64 “B” body; Mad Dog stopped producing these headers years ago) I would go with the round port heads.

Remember air speed / port velocity is not a constant. This is CFM and velocity based on numbers from Edelbrock.

Stan

I think chambers are just about the same. The exhaust on D-ports are kind of their down fall. Can’t remember exhaust flow numbers on D-ports but I do know round port can go 270 cfm. Maybe more not sure.

Sometimes I say things and just wish you guys would give me the reaction I am looking for ...

I would always go with round ports, and buy headers. D-ports and manifolds are going to be limited. A set of round port heads and a nice Hydraulic cam will make 500 hp, like falling out of a tree. 500 hp in street car is killer. And crazy street able. Thats just me. Are there good D-port combo out there sure, but you can bet they’ve ported. But E-head out of the box will make 500 hp and you don’t need a hydraulic roller cam.

From my personal experience, cost was the number one factor for going KRE D-port. Assembled Performer RPM's as cast were about 400-500 more than assembled as cast KRE D-ports when I purchased. I also trusted the products going into the KRE heads over the Edelbrock offerings.

I also already had a set of D-port headers. That would have added another 500-700 for headers and whatever exhaust work would have been necessary to get those set up with my existing exhaust at the time.

In 2015 when I was doing the top-end on my engine, HFT failure reports were rampant and almost nobody knew anything about why. I opted for a roller as a result which upped the cost. I didn't have faith I wouldn't lose a cam/lifter so I spent that extra I didn't spend for the round ports on the roller cam.

Very understandable. Sure you weren’t disappointed

I am not sure where the idea that you need 80 exhaust to intake comes from. I would guess the BES Pro Ports are about the top for an "E" head and they are no where close to 80%.

Stan

I think it may come down to the fact there are probably more street guys then race guys. Street guys can get the power they want from the D ports easy. Then you don't have to change your exhaust or choke. Those were my reasons.

There’s definitely more street guys then race guys. There’s a lot to take into account when you’re making that choice. None of it is cheap anymore either. I can understand if you have a car with no headers now, then having to do the modifications.

I know I've seen that ratio parroted here. The reasoning given is that as exhaust flow approaches 75% of intake flow, you can reduce the exhaust valve duration. A single pattern cam becomes an option at that point.

From what you posted, looks like 65% is the bogey for a max effort engine. So a 330CFM intake port only needs 215-220CFM from the exhaust at max lift. The edelbrock head posted earlier has about 65-70% I/E ratio at 550 lift I compared.

That tells me that a ported D-port exhaust isn't a major restriction on a N/A street motor. How many Pontiac street motors have over a 330CFM intake port?

The ratio of Exh to Intake flow a given combo needs is also very dependent on the motors compression ratio and the stoke employed .
It also seems that no one is factoring in the 3 to 5 extra % you can pick up in Exh flow by just bolting on the right size header tube.

A 68% Exh to Intake ratio that's right on edge of that so called 75% magic numbers then climbs to 73%.

If one wants to look at exhaust intake ratio to figure needed cam split they also need to know CR.

Stan