318 vs 360 exhaust manifold port size?

[Adam]

Does anyone know if the 360 exhaust manifolds have a larger port than a similar production 318 manifold. I’m working on an old Ramcharger with a 318. It’s very anemic with only 172 hp. I’m installing a better cam, and will do a dual exhaust system. It does have 9 to 1 compression and swirl port heads. Since the truck was available with both the 318 and the 360 would there be an advantage to using a similarly shaped 360 manifold? I don’t currently have loose ones laying around to compare port sizes.

 

[Chryco Psycho]

Yes , both the port size at the head & the outlet size into the pipe will be bigger on the 360 manifolds . Some of the best flow manifolds are the Magnum manifolds if you can fit them .

 

[Adam]

Thank you. I thought so, but Rockauto, eBay, etc, shows the same exhaust manifold for both 318 & 360 so I wasn’t sure.

update: I am unable to find a casting number for a 360 only manifold; they all say 318/360. I guess I will have to actually measure the exhaust ports for comparison.

 

[Chryco Psycho]

I know the Magnum 360 had a very large outlet diameter for a couple of years , hard to find now

 

[basketcase70]

FWIW I picked up a set of early (guessed to be from a 94 5.9) Magnum manifolds years ago from a private party who did not know what they were taken off of, and was not 100% sure of the exact model year either.
The outlet diameters choke down to around approximately 2 1/4” in the last inch or so before they couple to the head pipes, but there appears to be enough meat in the walls at that area to encrease the diameter slightly with a judicious application of a straight burr in a die grinder. Even if they can’t be brought out to a full 2 1/2”, the small and short restriction left would be pretty minimal and I would have no qualms running them with 2 1/2” diameter headpipes.

 

[Chryco Psycho]

I always port exhaust manifolds I see no reason to not open them up