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Old 01-29-2012, 07:04 PM
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1970 Pontiac Grand Prix Restomod

Hello all I'm working on a 1970 Grand Prix, I have a 455 bored 30 over, and was wondering if anyone has heard of "Header Manifolds". I have Hedman Headers to put on but have heard they leak. These Header Manifolds are said to work like Headers but fit like regular manifolds. Where can I get them?
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Old 01-29-2012, 07:19 PM
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I know Pontiac used cast iron headers on some engines. Perhaps this is "header manifolds"? I would check Performance Years catalog.

BT
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Old 01-29-2012, 07:24 PM
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This is in the wrong place for tech questions and it will probably be moved. In the meantime try Ran Air Restorations. I believe that the "F" body manifold fits the GP, but I would ask, just to be sure. By the way, they won't be cheap!

Bill
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Old 01-29-2012, 07:52 PM
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By the way Love the site. thanks for the info.
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Old 01-30-2012, 10:12 AM
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Sanderson makes shorty cast headers, but I'm not sure if they make them for your car/engine. I think they're for more common cars and engines.
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Old 01-30-2012, 11:30 AM
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Quote:
Originally Posted by billonwheels
Hello all I'm working on a 1970 Grand Prix, I have a 455 bored 30 over, and was wondering if anyone has heard of "Header Manifolds". I have Hedman Headers to put on but have heard they leak. These Header Manifolds are said to work like Headers but fit like regular manifolds. Where can I get them?
Back in the '60's Pontiac used (as did all the OM's) cast "headers" on selected engines to be used for racing where factory parts had to be used.

Some really expensive, rare manifolds were these ALUMINUM Pontiac pieces:


More stock headers HERE

But unless you have heads that are missing the end header flange bolt hole (which would not be original to your engine if it's a '70), a good set of headers like the Hedman will seal up fine. The problems come from inferior headers w/thin flanges, bad alignment or those to-be-avoided 3-tube headers that you'll see sold cheap.

FWIW, I had Hedman's on my last Pontiac and they sealed great- you do need to retighten after heat cycling until they take a set, and occasionally check them from then on. The exhaust system should have hangars that support the weight so the headers aren't taking it all.
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Old 01-30-2012, 12:03 PM
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1970 GP is an "E-Body" or "extended A-body". It has the same front and rear portions of the frame as the A-body, with about an 8" extension in the 'middle". The suspension components and mounting points are the same. The exhaust manifolds that "fit" are the '68-'70 "HO" manifolds for d-port heads, found on '68-'70 A-bodies with the high output engines (400, 428 and 455). The "long branch" manifolds pictured will NOT fit the '70.

Hedman "Hustlers" are okay headers. Not great. Today, Doug's are quite popular among the d-port crowd, and Hooker SuperComps are still the best "out of the box". What "fits" GTO of the era also fits GP.

FWIW

Jim
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Old 01-30-2012, 04:05 PM
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Hedman Headers, Magna flow Mufflers?

I think I'll try the Hedman Headers, its seems alot of people have had good luck with them. I'll try them since I already have them. Whats the thought on Magna Flow exhaust? Flow Masters rule the car shows around here, looking for a diffrent sound.....
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Old 01-31-2012, 02:10 PM
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Pontiac headers can be found from 1-5/8" to 2"- (Supercomp's to fit the '70 GP are (I believe) from 1-3/4" to 2"). Collectors are 3" or 3-1/2".

I've not seen any recommendations here at Hotrodders on what diameters would be best for the Pontiac 400 and 455 engines depending on the state of tune, i.e. stock/mild street cruiser, street performance w/some cam, and street strip w/cam, porting.

Maybe Mr P-Body could elaborate? This should be something that would help a lot of guys here.
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Old 02-01-2012, 07:06 AM
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For up to 450-500 HP, 1 3/4" headers are adequate with the d-port heads. Hooker stopped the 1 7/8" a few years ago, thinking the Pontiac "market" was dying. So, Doug's has been selling the snot out of 1 7/8" units. According to Eagle and Harland Sharpe, the market is actually growing at a rapid pace. I believe this is due to the competitive components that are now readily available.

For a mild 400, the 1 5/8" are barely adequate. I wouldn't recommend them for anything larger.

2" headers are readily available for the "round port" (Ram Air IV-style) heads. There were some 2" units made by Indian Adventures (now defunct) in the late '90s for the d-ports. They used an "adapter" not unlike those found for small block Chevys with such large tubes. I don't know of anyone making them now.

Okay?

Jim
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