302 gmc manifold problem

[JasonS]

I bought a new 302 gmc exhaust manifold from an online retailer to replace the dual exhaust on my 47 chevy pickup. Driveability is terrible without manifold heat. I mate the new exhaust and my old intake and the intake manifold is about an eighth of an inch back from the exhaust. I was told by Patrick Dykes of Patrick's Old Cars and Trucks that all 302 gmc exhaust manifolds were the same; this one is not. In fact, it is a "Clark" replacement. Anyway, were the military exhaust/ intake manifolds different?

 

[NDT]

I have run into this before, just not as severe. The old intake/exhaust assy may have been surfaced numerous times over the years, each time cutting .010 or more off. When you mate the old intake to the new exhaust, you get what you got.

 

[drlogistics]

Dito

 

[drlogistics]

Where did you get the exhaust manifold??

 

[JasonS]

It can't have been cut that much; there'd be nothing left of the intake flanges. If you move the intake such that it is flush with the exhaust, the spot faced areas between the outer exhaust/intake ports line up perfectly. Looks to me like a bad copy or there are differences between the civvy and mil manifolds. I got it from http://www.dukw.com/

 

[hendersond]

I'm assuming there were some differences in manifolds. I have seen some variances. I have one manifold with flange for a flat gasket and one for an exhaust doughnut. One looks a little smaller around the heat riser area. I'm thinking one is an aftermarket replacement. I'll look today and see a little closer.

Good reason to get the M211 out for a ride!

 

[hendersond]

Both manifolds look the same, They have the same casting numbers. The only difference is one was machined with a bevel to accept the exhaust doughnut and the other one is flat to accept the steel reinforced flat gasket.

 

[JasonS]

Got it installed and running. It takes a few modifications.

1) I had to elongate the holes in the exhaust manifold and in the intake manifold to allow the intake to move further inward towards the head. I used allen head bolts in place of the exhaust manifold studs due to lack of room to get a wrench in there. This still left a 1/16 gap.

2) I ground 1/8" off of the sides of the exhaust manifold flange to allow it to fit the studs between cylinders 1/2 and 5/6.

3) I doubled up the gaskets on the intake ports and between the intake/ exhaust manifolds, and bolted it together.

Works fine. In fact, it works MUCH better having exhaust heat on the intake manifold.

I've used the heat plates that the vendors sell with their tubular headers and they don't work. I've also used water heat but it takes awhile to get to temperature.

In the end, it takes a bit of work but this manifold is a good value and half the price the typical mil vendors chage for a used manifold..

 

[hendersond]

How much cash did you have to chuck out for that manifold?

 

[JasonS]

How much cash did you have to chuck out for that manifold?

$206 shipped. I didn't know that modifications were required when I bought it but it is still worth it to have a NEW one.