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Your thinking backwards here,
Equal length runners balances the cylinder flow so that power is smoother across the band....
Long runners make lots of torque lower, not higher RPM.....
For instance look at this engine.

SHO V6 Ford, it has twelve runners for 6 cylinders. At 3600 RPM it opens butterflies that allows the short runners to start working, this creates a very FLAT torque curve.
Look at 4 barrel intake manifolds, dual plane intakes have long runners and breath from idle to about 5000 rpm.

Then look at the single plane intakes they make power from 2500 to 7500 rpm typically.


What long runners do is promote better cylinder filling, it also gives a slight ramair effect the inertia of the air moving towards the cylinder will actually give a slight overcharge of the cylinder just before the valve closes. This port velocity is what makes torque numbers. Its also why a 5.0 Ford could make torque numbers it does. It has very long runners and they quit breathing about 5k rpm.

Just a little Engine dynamics 101.


I found this image of 4.0 intakes.