It is my understanding that Throttel bodies are waste of money unless you do roller rockers, headers, and head work.
Here is my story: I have a venom 500 - 67mm Throttle bodies, headers, K& N's, roller rockers, stock heads and 3:54 read gear.
Me n Eric, MTHAM ACR run at the track and without putting his car down, the guy is very good and very quick , on the long straights and my car can pull up on him and get a pass. So is it the gear or is my car breathing a little better??
In the lower RPM's, say under 3,000 I gain very little, then from that point on my car feels like it has a rocket up its butt - it just pulls like ...well enough said. So I can't explain it in technical terms but there seems to me, to be merit to the idea of enlarged throttle bodies - I think the question is, how big basis the modifications - now at this point, talk to Sean Roe or one of the tuners that are mentioned frequently (in a positive light) on this board.
Luck