Correct Factory Exhaust Manifolds 70 GMC K2500

[BILT4ME]

Originally Posted by seattle gmc

The heat riser is suposed to be on the passenger side. The dorman ramshorns do suck. I had a cracked manifold and bought a dorman replacement and it didn't fit well. The machining was so poor i couldn't get the center manifold bolts torqued down until i opened them up with my dremel. The bolt head was hiting the side of the manifold where they didnt machine enough metal away. And yes i had to plug the smog tube holes. Surprisingly i got another manifold from LMC and it fit well and didnt have any of the problems the doorman one did. I have no idea who manufactured it.

I guess you need to keep an eye the parts board or ebay for a straight dump ramshorn.

The manifolds from LMC are the Dorman ones.

I have been looking on eBay for originals, but I cannot determine exactly which version is "correct" and I cannot confirm if different casting numbers have the same size outlet/dimensions/features.

There are at least 6 casting numbers that MAY work. I have also found that certain years of Corvette ones are actually 2-1/2" outlet instead of the standard 1.9" or 2" outlet.

I have found a listing of every casting number and what it "goes to", but there are no pictures associated. So, if I had all the time in the world, I would cross reference this list, then use eBay to find pictures, but I still would not have confirmed dimensions unless I actually PURCHASED a few. When they are going for $45-$100 for ONE manifold, that's not going to happen.

I find it interesting that GM changed the casting number every two years, with little evidence as to what changes were made. The fact that it has a new casting number means it is NOT the same as another one. It COULD be just a superficial change, but at the cost of casting molds, It would be poor planning to change the castings that often.

Thanks for your input!

My original question till stands. What are the CORRECT straight dump manifold castings for a 1970 GMC K2500 with a 350 and 4 speed?