235 261 Chevrolet Dual Exhaust Header Manifold

A split manifold on a stove bolt Chevrolet 235 or 261 engine makes for a unique sound and increases breathing capacity, therefore slightly increasing horsepower.

The early Corvette came with what was called the Blue Flame Six. It had the dual exhaust manifold and three side draft carburetors.

Through the years, there have been a lot of standard manifolds split, and they were done in a wide range of fashion. Sometimes done with a plumbing elbow, just scabbed onto the side of the manifold with just an extra hole exiting the manifold.

There was a rear section offered for splitting the manifold that was actually a separate cast manifold. You would cut the original manifold just behind the heat riser and block it off at that point, making the process quite simple. These are quite rare to find, but make for a nice vintage correct look and are of pretty nice quality, although they don't really look like they match when finished.

I have an example here of a very nice original 235 manifold that has been split, using an original flange from another manifold. It has also been blocked off just behind the heat riser so as to make two separate chambers. In making two separate chambers, it gives the exhaust a definite cackle. If you have pressure equalizing between the chambers, it softens the sound greatly.

The welding of the cast iron is a tricky process. It is best done in conjunction with an oven for preheating and controlled slow cooling after the weld is done. It can be done by Brazing, cast iron welding or nickel allow welding. Keeping the manifold bolted to a head with the intake in place as well, provides for a great jig to prevent warping.

This example here has a very nice tight shaft for the heat riser, with almost no wear on it. Because it is quite an involved process to do a manifold like this, it is not worth the trouble to split one that is not in excellent condition. This one was welded together with nickel alloy rod. A final finish of VHT cast iron paint was applied. This coating holds up very well. I used it on my 1937 Chevy pickup manifold, several years and 30,000 miles ago.
                 Sold                                           For Sale $325

1 comment:

Unknown said...

Hi. Nice work---bet you used nickle 99 rod. Seen a lot of them done by brazing on a steel flanged piece of exhaust tubing---not cool. I`ve don quite a few in the distant past using ni-rod AND oxy-acetylene cast iron welding. Bolt it to a cyl. head and heat with a rosebud til red and start welding--gloves are mandatory. Really old school. Thanks for the post. Swede Johnson