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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old May 1st, 2017, 06:25 PM
arepoff arepoff is offline
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Default Magnum Exhaust Manifolds

Will the magnum exhaust manifolds bolt on to a 305E?
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  #2  
Old May 2nd, 2017, 06:57 AM
bigblockv6 bigblockv6 is online now
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Default Re: Magnum Exhaust Manifolds

Magnum exhaust manifolds will not match up with the small port heads. If you're looking for some freer flowing manifolds use the larger series I Beam manifolds that were used on all 351C, 379, small port non Magnum 401(1960-65) or small port non Magnum 478(1962-65)
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  #3  
Old May 2nd, 2017, 02:17 PM
arepoff arepoff is offline
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Default Re: Magnum Exhaust Manifolds

thank you for the info.
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  #4  
Old May 8th, 2017, 03:11 AM
1972RedNeck 1972RedNeck is online now
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Default Re: Magnum Exhaust Manifolds

Quote:
Originally Posted by bigblockv6 View Post
Magnum exhaust manifolds will not match up with the small port heads. If you're looking for some freer flowing manifolds use the larger series I Beam manifolds that were used on all 351C, 379, small port non Magnum 401(1960-65) or small port non Magnum 478(1962-65)
Why not? Is the bolt pattern not the same? How about the bolt to port location relation?
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Old May 8th, 2017, 03:55 AM
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Default Re: Magnum Exhaust Manifolds

Why is because the small head ports are not machined to accept the larger port manifolds. Physically they may bolt up but the surface will be uneven. Like I mentioned using the 351C,379 non Magnum 401 & 478 I Beam manifolds will work, they are the same free flowing design as the Magnum manifolds other than the ports at the mating surface are smaller which is just fine.
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Old May 17th, 2017, 04:31 AM
1972RedNeck 1972RedNeck is online now
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Default Re: Magnum Exhaust Manifolds

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Originally Posted by bigblockv6 View Post
Why is because the small head ports are not machined to accept the larger port manifolds. Physically they may bolt up but the surface will be uneven. Like I mentioned using the 351C,379 non Magnum 401 & 478 I Beam manifolds will work, they are the same free flowing design as the Magnum manifolds other than the ports at the mating surface are smaller which is just fine.
So the head ports will be centered in the manifold ports, it's just that the head ports are smaller than the manifold ports? Will that actually negatively affect performance at all?
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Old May 17th, 2017, 04:50 AM
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Default Re: Magnum Exhaust Manifolds

The problem is as I mentioned previously the smaller port heads are not machined to accept the larger port manifolds, therefore the mating surface is uneven, it will not seal up and it will leak:pullinghairout. You will get the same advantage with the small port I beam manifolds used on 351C, 379 and non Magnum 401 & 478 engines as you will with the larger Magnum manifolds as both style manifolds have the same free flowing design other than at the mating of the ports. How much more do I have to make this clear to you???
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Old May 17th, 2017, 05:48 AM
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Default Re: Magnum Exhaust Manifolds

Here are a couple pictures that I found from an album.....here you can see the major differences between the non mag and magnum manifold ports. Like Pete said, the Mating surfaces will not match causing leaks.
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Old June 1st, 2017, 04:52 AM
1972RedNeck 1972RedNeck is online now
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Default Re: Magnum Exhaust Manifolds

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Originally Posted by TJ's GMC View Post
Here are a couple pictures that I found from an album.....here you can see the major differences between the non mag and magnum manifold ports. Like Pete said, the Mating surfaces will not match causing leaks.
Ah, a picture worth a thousand words. I was thinking the ports were similar, just that the Magnums were bigger.
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Old June 1st, 2017, 04:59 AM
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Default Re: Magnum Exhaust Manifolds

Yes pictures are worth a thousand words but I did a little experimenting and found out later 305 heads are machined to accept the large port Magnum exhaust manifolds. The 305E I pulled out of my 68 has heads that are machined and the manifolds fit flush to the heads.
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