THe holley one i saw is a 670, so what is the amount stock? Also there are two, one for the 305, and one for the 350, they are both 670's whats the diff?

 

the only difference between the 350 and 305 holley units are the injectors. I believe the stock TBI flows at around 450-500 cfm with the Ultimate TBI mods. The stock unit is fine unless you are producing over 300 HP

 

I've read a tech section in Hot Rod (actually a letter) and a guy asked if TBI would be OK on his 383.

Turbo City suggested that he use the 454 TBI because it flowed ~620 cfm.

They said a stock 305/350 flows ~535cfm, and there modified TBI flows ~585cfm. Obviously they flowed them for a comparison, but who knows if they had the injector pod in, or if they used 3.0 inHg or 1.5?

So that's what they claim. 535 ain't bad, but 585 is better. 620 for a cheap used 454 TBI is pretty good. If it's good for a 383, then it's gotta be good for a 350, up to a certain HP level anyway.

AJ

 

I have been told 525cfm

 

I think a bone stock 1 11/16" TBI is 450 CFM. Not 100% sure. Also, I believe CFM for TBI is measured differently than a carb, so keep in mind a 450 CFM TBI does not = a 450 carb. I don't know how they measure it differently or why.

 

2 barrel carbs and throttle bodies are measured at a 3" pressure drop (the pressure under the carb is 3 inches of mercury less than the pressure over the carb). 4 barrel carbs and throttle bodies are measured at 1.5" pressure drop. I don't know why they do it differently either. Holley, by the way, rates their 1.68" TBI unit at 400cfm.

 

Well how does Holley measure theirs? If they flow it at 1.5 inHg, then that converts to ~565 cfm at 3 inHg. That's a little on the high side IMO, but do-able without the injector pod in there.

Theoretically, the reason they use 3 inHg on 2 barrel carbs/TBs is because the suction on a 2 barrel carb will be higher due to the engine trying harder to pull more air through a smaller area.

BUT!!! I think they do it to make the 2 barrel carbs look better to the general public so that they can still sell them.

The common 'Joe' doesn't look at the rate of flow and the amount of drop at the same time. Anyone who knows the diff. and who looks for it, will mainly be looking at 4 barrels anyway. So it's really a marketing ploy. At least IMHO.

AJ