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Old 06-19-08, 02:40AM   #1
INJUNTOM
 
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Default D port head discussion

Everytime I see the term "D port", it makes me think "why does the the shape of the exhaust port HAVE to indicate what the intake is capable of in flow?".


Follow me here....Let's say if the Tiger head were to have been designed with a D shaped exhaust port, but the intake had been designed the same as it was and is, then what would the intake have flowed? The same because it would have been built with the same intake runner that it actually has right?

A D port head doesn't necessarily mean it has to be capable of less performance JUST because it has a D shaped exhaust port does it?

Couldn't it have very well been built with same intake runner as a Tiger, E head, or maybe even a CV1?

Not saying that it would make sense to build it that way, but obviously there was enough extra material there to be able to get those numbers.

Another question is this? Considering an acceptable intake to exhaust flow ratio, what is the most you are going to get out of a D port exhaust in terms of exhaust flow? How much intake flow could you have and still have an acceptable intake to exhaust flow ratio?

Mostly talking in terms of aftermarket D ports, but some of my other questions will also pertain to iron D ports as well.
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Old 06-19-08, 02:56AM   #2
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I think it mainly depends on if the two middle ports if they are able to keep up with the outer ones. You could make any aftermarket head a D port. I think I read that the old SD 421s had the two center port bolt holes moved out to keep flow more even between ports. And why would you need to keep the port shape the same as stock? Outers are oval and centers being D, especially with an aftermarket D port. That is if there is enough "meat" to match them all.
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Old 06-19-08, 11:04PM   #3
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i am going to be running some 280cfm @ .600 iron 4x heads and they flow 220 ex i don't know how much more is left but the heads i am getting have adapters to run round port headers so i'm not stuck with tiny exhaust, the middle ports are too close together from what ive been told to get a real 2'' or bigger primary header on, you can do stepped headers though, FWIW aftermarket D-ports are not really comparable to factory D ports IMHO
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Old 06-21-08, 01:32AM   #4
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InjunTom- Since you've started an 'Engine Tech' thread related to D-port heads, maybe we should first "clear the air" regarding terminology?

If we Pontiac-faithful were to stray outside our own little world, we might be puzzled by "outsiders" mentioning D-port exhausts of other brands' heads- typically exhaust ports with a laid-down 'D' shape (such as the CV-1 ports). Similarly, they might be surprised to hear us talk of stock Pontiac heads being "D-port"- unless they realize we're talking about the upright-'D' shapes of only our center exhaust ports.

[Too bad we didn't start out decades ago with a non-ambiguous name for Pontiac heads- "siamese-center-ports" or some such thing; except that would need an "almost-" prefix, since center ports of '55-58 heads actually were siamesed!]

Okay, I'm done now- proceed with the discussion!

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Old 06-21-08, 02:51AM   #5
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yeah got some "laid down" d ports on a 350 LT1 chevy aluminum heads and all, straight from GM. People probably think us pontiac guys have "good" factory heads if they overhear us talk.
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Old 06-21-08, 03:17AM   #6
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This is a Pontiac site, so D-PORTS are cast iron heads. Anyone that don't get it don't need tobe on here. All after market heads are of the round port design as far as exhaust headers. OK?
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Old 06-21-08, 03:25AM   #7
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This is stupid.
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Old 06-21-08, 03:26AM   #8
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And Kaufmann Alum-D-Ports
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Old 06-21-08, 03:43AM   #9
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Quote:
Originally Posted by Randuss View Post
This is stupid.
How so?
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Old 06-21-08, 04:20AM   #10
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Hmmmm maybe the chevy site would suite you better since this pontiac site is so stupid to you?
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Old 06-21-08, 05:31AM   #11
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Quote:
Originally Posted by Pontiac Jack View Post
InjunTom- Since you've started an 'Engine Tech' thread related to D-port heads, maybe we should first "clear the air" regarding terminology?

If we Pontiac-faithful were to stray outside our own little world, we might be puzzled by "outsiders" mentioning D-port exhausts of other brands' heads- typically exhaust ports with a laid-down 'D' shape (such as the CV-1 ports). Similarly, they might be surprised to hear us talk of stock Pontiac heads being "D-port"- unless they realize we're talking about the upright-'D' shapes of only our center exhaust ports.

[Too bad we didn't start out decades ago with a non-ambiguous name for Pontiac heads- "siamese-center-ports" or some such thing; except that would need an "almost-" prefix, since center ports of '55-58 heads actually were siamesed!]

Okay, I'm done now- proceed with the discussion!
But we were first Jack!

And yep, the "laid down" D was a good way to go. Keep the floor as high as possible and still flow adequately.

Seems to me that the only real hurdle for a D port Pontiac is the configuration the headers have to be in to fit....At least on 90% of the engines out there.
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Old 06-21-08, 05:32AM   #12
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Quote:
Originally Posted by 464GP69 View Post
Hmmmm maybe the chevy site would suite you better since this pontiac site is so stupid to you?
He musta been talking about the goofy comments he was making.

Didn't anyone tell you to paint in a well ventiated area?
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Old 06-21-08, 11:31AM   #13
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Not being an Engineer back in the day in the 50's. I think it was common thinking to siamese the center ports. Clearance for plugs stability for cast exhaust manifolds, etc. Chevy, Olds, Buick, Pontiac.
Even the First Ford Y block engine had the center ports closer together. Not untill the SB Ford 221 and 260 did Ford redesign the ports.
I think the different divisions just took each others design and changed them up just for each division.
Chevy already had the square siamese center ports. I don't think it had anything to do with HP potential. Just a way of thinking back then and geting water flow, plugs, manifolds, etc to fit a package.


Just my 2 cents.

Whether round or D-port for the Pontiac the intake port design basically never changed from D to round much.

Remember that Chevy bought the rights to use the Pontiac rocker arm design so there was interchanging of ideas within the departments.
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