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from what i understand, the ipd version actually disables one of the intake resonance flappers (designed to tune the intake at low rpm) the idea being to flow max air at high rpm (gets all obstructions - like resonance flappers - out of the way). as a result, the ipd plenum is acknowledged to have a low rpm torque dip (lots of dialogue at planet 9 where there are more cayman applications) presumably associated with the loss of low rpm tuning. ipd's solution to this is to use a larger throttle body which works like a sprint booster - more throttle sooner - to get you past the dip quicker.
comparing ipd (softronic make something similar) to the tt, there were some fluid analysis graphs posted in a similar thread, and my take was ...
air flowing from the throttle body hits the plenum and turns left or turns right into the two manifolds.
the stock plenum has a hard surface on the outside of this turn, and a 90 degree hard corner on the inside of the turn.
the airflow will adapt to this by cavitating on both the outside and inside of the turn, reducing cross-sectional area available for airflow into both manifolds.
the big offender is on the inside of the turn, where the turbulence on the inside of the bend dramatically constricts the airflow.
on the outside of the bend, the area of cavitation looks remarkably like the little piece of plastic pedro puts into the tt. my thinking is that the airflow will naturally do that the tt tries to do, and that there is no benefit.
the ipd product addresses the inside of the bend also, by replacing the 90 degree hard corner with a gradual, smooth curve. this will improve airflow.
given that, one would think that a muffler shop could fabricate a y-pipe with an aos bung to do exactly the same thing. as initially noted, however, some low rpm torque is lost with this approach.
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