I found a guy locally that will polish the top and underside of my stock plenum. My question though is there a benefit to polishing the under side portion of the plenum or is it just a waste of money?

 

some roughness helps air to roll and eliminates stagnant areas; i wouldn't do it.

 

Polishing is just for dress up purpose only. No gain in performance.

 

what are you guys talking about, instant 50 to the wheels, just like stickers, best bang for your buck mod in my opinion. +1 for dress up only

 

No it's not worth your money, on an N/A car the restriction isn't the plenum, it's the plenum design.

 

you are kidding right? polish plenum is only for *bling* *bling* purpose....

unless you are talking about port&polish the lower intake manifold..

 

In theory, a polished plenum would actually perform worse. Why? Heat. A polished plenum (or anything polished) does not radiate heat as good as an unpolished one. The polished plenum would be a few degrees hotter so it would warm the incoming air more. Keep in mind that the difference is small when you consider the relatively low temperature and high air flow rate through the plenum.