what size TB=750cfm?
 

if a motor made the best power with a 750 carb but i wanted to use EFI and i was going to do a spider style intake what size TB would i use?

I've seen the following numbers from bench flow tests:

70mm BBK flowed 726
75mm Accufab flowed 845

Guess you'll be looking for a 71.3mm ;)

Hope this helps ya out.

This is pretty good info.
http://www.accufabracing.com/faqs.htm