Quote:
Originally Posted by Jake Raby
We use modified IPD arrangements on most Stage II engines. In my experience, until you add 400ccs, a point of compression, some real port work and etc , the gains are minimal.
I have seen stock engines make less power with them, back to back on the dyno.
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I understand that the IPD arrangement has the potential to direct and accelerate the intake air left and right giving more "authority" to the charge, but I have always been concerned that it would restrict acoustic pulses side to side (perhaps this is not a valid concern). Especially when the resonant flap in the cross tube is shut. One can see that the design has evolved with different types of relief holes through the "divider blade" perhaps to mitigate this very issue.
Just a guess:
The engine is drawing the intake air in and the divider could potentially disrupt side to side (one plenum feeding the other) cylinder filling in certain cases (engine rpm and flow rates).
It would look like this design would be much better suit to forced induction where bank to bank acoustics would be covered off by positive pressure before the divider blade