That video has one HUGE error that we all know of.
At 6:16 it says 'speeded up in one place, slowed down in another to keep the mixture uniform SO THE SAME AMOUNT OF GAS GETS INTO EACH CYLINDER."
REALLY?????? We all know that the intake manifolds do nothing of the sort.... BUT AT THE TIME it was believed to be true.
If you believe that GM/GMC engineers had everything so perfect that every widget on the motor was perfect in design and function then you are in a fantasy land. In the 40's motors were still in their infancy and MARKETING cars was more important than the science behind them. There were no CAFE standards to meet and no safety requirements. The NHTS Agency wasn't enacted till 1965.
As my manuals state the operation of the heat riser is purely automatic... meaning you could keep it off and still run the motor fine.
I do believe that the bottom of the intake does derive a benefit of boiling off the pooled gas (as the charged incoming air makes that 90deg turn some fuel will drop out of suspension... its the same basic premise of how the oil bath air cleaners work). But its not a meter heat that can be shut off or turned on... the exhaust manifold will reach some quiescent state and that would be completely out of the risers control.
