72 340 pass side manifold

65 Cuda 340 said

As for performance, I'm surprised someone hasn't posted the Mopar Muscle (I think) dyno testing of a 300 hp crate Magnum engine with different exhaust. According to them, the best 340 exhaust manifolds were only marginally better than LA 318 manifolds, and headers were only maybe ten hp better.

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I think maybe that test isn't valid. I am concluding this based on the dyno test on YouTube where a JY 5.9 was compared to a 300hp crate motor and they made within 1 hp of each other.

Exhibit A - even though the crate motor had a better horsepower producing intake (in theory), they made the same power. Everything else should have been the same between the motors other than the intake. So the long runner beer barrel intake isn't the limiting factor.

Exhibit B - the same guy swapped a mild (like 262 duration) cam into the 300 hp crate motor and made 50-60 more horsepower. So I think the cam is the real bottleneck.

Based on this, I think the stock cam is just a little bumpier than a broomstick. And with such a small cam, I doubt the difference between the 318 manifolds and the 340 ones can accurately be evaluated. Same with the headers.

Also, Engine Masters ran that same crate motor with the better cam and saw a difference of 24 hp and 6 lb/#'s between the stock beer barrel intake and the dual plane M1 (with a spacer). So the dual plane is better at making top end horsepower.

All that to say, I'm not going to sell my freeflows and buy some 318 manifolds and pocket the difference because I think (in the end) the 340 manifolds probably make more power than the 318 ones. Regardless of what that test says.