Wanted Right side 340 HI-PO exhaust manifold

I would like to bring up something that nobody ever talks about RE these "hi-po" passenger side manifolds.

There was an exhaust manifold test in Mopar Muscle magazine one time in which they dyno-tested all the different OEM exhaust manifolds that fit 318/340/360 motors, including testing a dyno "mule" engine using TWO passenger side manifolds just to see what the difference was between using two of them (which would be impossible on a car) and then, one right-side and one left-side manifold, which was the "norm."

The difference was significant.. something like 10 horsepower, using two of the "right side" manifolds. Of course, you can't run that setup, but consider this: If those right-side manifolds flow THAT MUCH BETTER than the left side (and obviously, they do) what do you think is happening to the backpressure created on the right side, and the left, driving down the road at a pretty good clip???

The pressure differential between the right side and the left will force a lot of hot exhaust gas through the under-carb crossover, constantly superheating that part of the intake manifold, if you have a manifold that has that crossover, and all the OEM manifolds do.

Replacing that hi-po right side manifold with a '71-up '360"-style manifold would be a step in the right direction, and while it might not cure the problem, it would certainly make for less of a problem.

If your intake manifold is an aftermarket piece with no crossover, then that problem wouldn't exist.

But, a lot of people who use cast iron manifolds also use the stock, cast-iron intake manifolds and lust after these header-style right-hand early 340 mainfolds without thinking it through.

I don't think all that hot exhaust gas is going to do anything good for the carburetor or intake ports in a stock manifold, especially, on a hot day. Talk about inviting vapor lock...

So, think twice before you bolt one of these "highly-desirable" early 340 right-side manifolds on an engine that has an intake with a crossover passage. Might not be the best thing you could do for your motor...