[pastry_chef]

Hi folks,

My first question is... has anyone measured the intake and exhaust port lengths (from entry to seat) of factory D-port runners?

What method did you use to measure?

Are the lengths about equal to the E-heads?

Also, in the hand of an experienced porter on average how many hours of work to get from stock (plain dport) to 240-250 cfm flow @ 28 inches?

Thanks.

[theoldone]

I took a bone stock small-valve Pontiac D-port head, from an early 1970's 455- I put 2.19 intakes and 1.74 exhausts in it (cut from 1.77)- ported it to RA IV intake height, and straightened the exhaust and intake a bit on the sides, and cleaned up the bowls, and widened the short turn area. After about 30 hours of work they flowed around 235 cfm intake- that was doing all 8 ports intake/exhaust. Not bad for heads that people were throwing away at one time.

The port length is about 4" on the original Pontiac heads. To that you must add the intake manifold port length as well to get a total- it sounds like you are figuring average intake port diameter ?

A Pontiac motor likes an oversize intake port- it dampens the reversion caused by the long stroke 455 engine, and also helps counter the less than optimum chamber design.

The E-heads will have the same port length as the standard iron head.

[pastry_chef]

Thanks oldone,

So.. would that be 4 inch length on both intake and exhaust ports?

The 4 inch length on the intake would certainly help explain why the pontiacs dont get choked for CSA -cross sectional area with the small runner volume.

My primary reason for wanting to know is to play with Engine Analyzer a little.

I believe software had a 'head file' for Edelbrocks that was telling me a 6.5 inch intake port length. I was justified in thinking it was incorrect.

I have a saved post contributed by I believe Tom V, which states lengths of a few popular intake manifold ports. I think the Edel Rpm was 6.3 inches or so..

Thanks again.

** Actually come to think of it, I am also missing the typical d-port head EXHAUST port volume. I will be using an d-port intake volume figure of about 165 cc's (mild port) for a 670 casting to be specific.

[theoldone]

yes, the exhaust port is approx. 4" long as well

[Steve C.]

The Engine Analyzer v3 program lists the port length as 4.7 on the Edelbrock and Pontiac heads.

Of interest, early on I was told the port length on the KRE D-port head was 5.0" ..... but since then I have also heard contrdicting info.