its a throttle body spacer for a duramax

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33558&item=7944880746&rd=1

There's a company that sells something called a TAG that does the exact opposite. It's a straight thru honeycomb grid like a catalytic convertor to straghten air out just before it enters the turbo. They say it doesn't neccessarily improve performance but it seems to run smoother.

Well, since the Duramax has no "throttle body" and since there is absolutely nothing but compressed intake air prior to our cylinders (where the fuel is injected under compression - sort of like a DIESEL) this is snake-oil bunk. (Quite cute, though.) Gassers rely upon a correct stoichiometric ratio of fuel/air mixed prior to intake into the cylinder in the throttle body or intake runners. There's some slight chance that a bit of vortex mixing could improve the mix, but no chance in a diesel.

and with "0" feedback

If only the General knew of this device :).

If they really worked wouldnt the manufacturers use them to improve their fleet MPG averages?