The other major factor is the skin friction drag inside
the runner tubes. Four, 1.5 inch diameter runners, have four
times the surface area and skin friction drag as two 2 inch diameter
runners if my arithmetic is right. Probably more as the
air velocity could be higher. This increases the pumping losses.
The high power RX8 six port/runner engine is even more of a
nightmare. Mazda had to do it to get more torque at 2000 and
3000 RPM for car use. The four port/runner RX8 engine is worse
as the breathing is becoming limited over about 6000 to 7000 RPM.

I get 1.5 times more surface area per unit length on four 1.5" pipes
(4*pi*1.5) compared to two 2" pipes (2*pi*2).  Cross-sectional area goes
up from 2*pi to 2.25*pi.  Am I looking at this wrong?


Dave Detty

That looks right. Not as bad as I guessed.

Paul Lamar ...No rotor no motor.

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