I just bought a Camaro that someone stuffed a late 80's Chevy truck 350tbi in. I do believe these TBI's flow 530 CFM...so I was looking at the Holley 670cfm but started to wonder about a 454tbi from an old Chevy truck, how much do they flow? Is Holley just making a 454tbi and selling it as a performance upgrade to a 350 motor?

 

It would be very easy and cheap for you to port the larger stock TB unit, but keep in mind that the major limitation to air flow is in the TBI cylinder heads. Putting the money into the Holley unit wouldn't really pay off while using stock TBI heads.

 

I already planed on changing the heads and cam but then my tbi is a bottle neck and I dont want to switch to a carb. What I need to know is if the $750 Holley 670cfm unit is the same as the $75 454 tbi I can get at a junk yard.

 

All of the information I have says that the BBC stock TBI has 2" bores and flows 670 CFM @ 1.5" Hg.

The only data I lack on this is my own personal measurement of the larger TBI bore, because I don't have one on hand right now.

The only other verification you could get is to find someone with the larger factory TBI and have them measure the bore diameter.
If it is 2", then it is the same as the Holley 670 CFM unit.

If you don't know anyone with one, I'd go to the junkyard with my slide caliper and grab one.

There is also this note about the injectors from RBob. He suggests using the earlier factory injectors, or the later Holley injector units.