Has anyone thought of having an underbody cover (not sure if that's the correct wording) like the GT-R has built for their G.

 

It is called and Underbody diffuser.

This would keep all that crap off your exhaust manifold, but the G already has a low enough coefficient of drag that it wouldn't really help the G at speeds it is capable of... see below.

They look cool on race cars, but that is really the only place you should find them. We have the tollboothwilley covers and stock underbody aero kit diffusers.

http://www.caranddriver.com/features...y-suck-feature

 

Thanks