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A common misconception is that headers only influence the top end.
Another common misconception is that headers only reduce power by reducing restrictions in the exhaust system.

Dyno tests have shown that shorty headers make more power than manifolds and long tube headers make more power than shorties. It has to do with the length of time the exhaust pulse travels in its own tube. A good long tube header will not only increase power above the torque peak, but it also increases torque below the torque peak. This low rpm increase clearly has little to do with flow restriction.

The oldsmobile head is an example. The center two exhaust ports are run together in the head and come out as one wider port which should lower restriction for those two ports. However, it is always advantageous to divide the ports. There is significant cross-talk between the two which interrupts something, probably scavenging during overlap. Flathead fords also had the center two exhast ports run together. In the flathead crowd it was a well-known modification to run a piece of sheet metal up that center port to divide the sides and increase performance.

There's more to an exhaust system than restriction.

R.

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I am aware of all that, yet my observations are still correct. I presume that you meant to say "increase power by reducing restrictions". Restriction isn't the ONLY part of the equation.....but it is the most important part, esp. when comparing relatively restrictive stock exhaust systems.



Dave