I,ve seen a few engine bay photo's on this forum and UK forums where the standard induction has been replaced by hard pipes and open filter kits, and what I think is the air pump return has been plumbed into the new kit ?
Firstly the large pipe from under the UIM is the air pump return YES / NO ? and if YES this air will be hot. ?? Therefore is it a good idea to pump hot air back into your induction when the IC is doing its best to cool it ??.
I noticed on the standard air box this return is fed into a seperate compartment within the airbox and vented to air. Was this not to isolate the hot air ??
Could be I'm talking *****! please let me know...nicely.

Bob ( UK )

 

Ideally, yes, it's not a good idea to pump hot air back into intake.

Basically, the aftermarket intakes do it for noise suppression. Leaving the line open, it makes a loud MOOO'ing sound like a cow. Obviously, that's an undesirable sound for a sports car. There are some alternatives which people use:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/eliminate-air-pump-moo-%241-1-minute-486061/

Dale's site is having an issue right now, but you can see the picture I posted which is basically what Dale's write-up talks about.