Modified Stock Intake Manifolds

Bob

Team Member
Moderator
I am looking for suggestions or examples of modified GM intake manifold for a 455 build.
I have found this one on the web:
pontiac modified intake.jpg
It looks about what I would expect.

We also have an example of a modified Nailhead dual quad manifold on the site:

I want the original appearance and drivablility. I was thinking that perhaps I should just open up the secondary section of the manifold and leave the primaries alone.

What do you think?
 
Like you, I have have painted aftermarket manifold to match the engine color, but I want to run an original cast iron manifold.

You have modified plenum in a manner similar to the idea I was considering , of course, with the stock manifold you start with a much more complicated webbing.
 
If that is how Gessler did it, that is how I would do it. Greg knows flow. Did it come with any flow numbers and were the ports flow matched Larry?
 
If that is how Gessler did it, that is how I would do it. Greg knows flow. Did it come with any flow numbers and were the ports flow matched Larry?

No flow numbers for the intake. I switched to the TA aluminum heads at the same time. They flowed 313/225 @ .550 lift. That combination with the Q-jet put me into the mid 12's at 107 MPH. My previous best with stock iron Stage1 heads was low 13's at 101 MPH.
 
I think those stock manifold runners topped out about 250 or 270 when flow matched. I remember a GS-X-Tra with a ported flow matched intake comparison. I wouldn't know where to find it now, but it would be interesting to see again.
 
I found this bit, coincidently by Gessler on a stock Buick intake here:

The intake, Buick casting number 1238323, got a thorough going-over as well. The plenum was opened on a Bridgeport mill, and the divider wall was lowered 31/44 inch to reduce torque and allow breathing at higher revs. It's also been port-matched to the heads. "Most all factory dual-plane intakes have some runners that flow a lot less than the others. On a Buick 455, it's the 2 and 3 cylinders. So I work on these two more than the others, and even the plenum is modified to help out in the equalization.

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So, while no pictures were shown, it would sound as though he probably hogged out everything, then lower the center plenum about 3/4". I have done this, but was wondering if anyone has kept some of the primary area intact, considering huge secondaries on the Rochester and it's efficient primaries.
 
I found two articles on various 455 Intake manifold flow and one that had a HP/TQ comparison:
 

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