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 Intake / Carb and Fuel Delivery Tech
 Finding cracks in Pontiac cast iron intake manifol
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beertracker
Cochise

350 Posts

Posted - 13 Sep 2014 :  3:25:24 PM  Show Profile  Reply with Quote
I have a 1970 Pontiac 4 barrel cast iron intake manifold. The surface is all cleaned up so checking for exterior cracks should be easy. So how do you check for interior cracks in the plenum and runners and those places you can't see? Is magnafluxing a option? How expensive is that?

Are these old cast iron intakes prone to cracking or am I just wasting my time. I wanted to use it so my engine close to original.

I want a LS engine in my Pontiac

Phil
The Great White Buffalo

USA
7216 Posts

Posted - 13 Sep 2014 :  6:41:51 PM  Show Profile  Reply with Quote
If you're concerned just do a visual check. They're not typically a problem unlike say, a cast iron Chris Craft 'Q' intake. :-(

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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beertracker
Cochise

350 Posts

Posted - 13 Sep 2014 :  8:53:06 PM  Show Profile  Reply with Quote
Wondering how many of you run Pontiac oem cast iron intakes? I could see some one using the old manifold for nostalgic reasons provided it not cracked.

I want a LS engine in my Pontiac

Edited by - beertracker on 17 Sep 2014 11:26:51 AM
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cortcomp
Coyote

USA
5335 Posts

Posted - 13 Sep 2014 :  8:59:50 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
The stock is actually equal to or better than many of the aftermarket ones, the reason i prefer the RPM to stock (they are close in performance) is that the stock is qjet only and the RPM can take spread or squarebore carbs. Likely never needed since i run a qjet, never know.
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Phil
The Great White Buffalo

USA
7216 Posts

Posted - 16 Sep 2014 :  1:56:33 PM  Show Profile  Reply with Quote
Agreed, the stock unit is very hard to beat for most applications on the street and street/strip. Hood clearance is yet another advantage in many vehicles.

If weight is a concern, the water crossover can be removed and an aluminum one used in its place. If eliminating the exhaust crossover in the heads, it can be cut off the intake and cleaned up via some grinding. Then I would send it out to SD for their CNC special if you want to max. out its potential.

But I have had excellent street results with untouched 68-71 intakes, even on 350's.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.

Edited by - Phil on 16 Sep 2014 1:57:36 PM
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Cliff R
Cochise

USA
535 Posts

Posted - 22 Sep 2014 :  07:51:18 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
I like the RPM intake, but they made it just over an 1" taller than a factory intake, so it can be a poor fit for some set-ups, Shaker and Ram Air, etc.

I've found thru dyno and drag strip testing that a stock intake is fine for most of these engines, and there is little if any advantage of using an RPM under about 500hp.

A few years ago, we built a 428 (440cid) engine and back to back dyno tested 3 intakes on it. My iron intake, an HO "re-pop", and the Edelbrock RPM. My iron intake and the HO were modified under the carb to the same apprx size/shape as the RPM, but stock/unported runners. All 3 intakes were port matched to a stock Felpro blue intake gasket.

The HO intake made 487hp, the RPM made 491hp, and my own iron intake made 497hp.

With this in mind, how many folks go to the RPM then have to "cobble" up all sorts of things to get it to fit, like special air cleaner/Shaker assemblies, etc........Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.
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Merrik66
Cochise

USA
370 Posts

Posted - 23 Sep 2014 :  01:33:58 AM  Show Profile  Reply with Quote
Are there any "real" differences in the runner/shape/volume of q jet intake from 68' to around 74'? I have a 68' and a 72' ...any pros or cons between those years? The 68' from a 428 and the 72' from a 455.
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Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 23 Sep 2014 :  10:27:11 AM  Show Profile  Reply with Quote
The 73 and newer egr intakes are less desirable. They also use a lower profile valley pan for clearance. The egr pluming creates a bulge in the right plenum. Some say it creates a small restriction to the #8 cylinder when the right secondary blade is fully open. But dyno tests show no significant differences between the manifolds.
If using a divorced choke carb with separate heat stove, the 68 manifold is needed. With the newer q-jet with an integrated choke housing, the 72 manifold will give a cleaner look. When using mismatched manifolds and cylinder heads, some cobbling may be needed to seal the exhaust crossover. There is a chart some where at PSP telling witch intake gaskets are used with the different combinations.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 23 Sep 2014 11:12:54 AM
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Merrik66
Cochise

USA
370 Posts

Posted - 23 Sep 2014 :  10:53:03 AM  Show Profile  Reply with Quote
Good info blued..exactly what I was curious about.
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