At the point that air is flowing through the IPD pieces there's no fuel, it's dry air mass. Frankly I'd like to see dyno results with an IPD piece back to back with same size throttlebody that shows definitive gains without unstrapping the car from the dyno.

IMO gains are primarily in the throttlebody, y-pipe is also some restriction depending on power level. I think I'm of the school of thought that says polish it although perhaps some turbulence is good?

Porting w/g pieces on internal gates and polishing the internals seems like a good idea to me. Perhaps if I retain the turbo I've got this will become a Winter project

 

Ah yes. My memory comes from my old GTO days with a Quadrajet and cast iron intake.

Cheers!
Chris