Modified Stock Intake Manifolds

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?
 

LARRY70GS

Active Member
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.
 
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