How much more or Less power would a TBI have over a 4-barrel holly 650? Opinions, remarks?

 

Given that fuel is fuel and air is air and both are wetflow systems id say theyd be nearly equal, or at least close to one another. This, of course, assumes that each are properly tuned and the user is using a tbi and carb that both have similar flow rates.

 

A 4V Holley 650 flows 650 cfm.

A Holley 670 TB flows 670 cfm.

I'm not sure, but I think that's how it works.

BTW, what engine are we talking about? A SB 302 with 11.5:1 compression, or a SB 400 with 8.5:1?

 

I think the flow ratings are different between a 2BBl & a 4BBL. If you do a search I think this has been discussed & argued over before

 

2V and 4V carbs, yes. They're different.

4V carb and 2 bore TB, no. They're the same.

The real question lies in whether the 670 was flow tested with or without the injectors in place.

 

Cool! Learn something new everyday. Thanks man

 

I saw flowtest results of a TBI with and w/o an injector pod. Didnt really seem to make that much of a difference. There was a slight drop in flow rate but nothing drastic.

 

i always thought the TBI and carbs were rated at different pressures? dont know the physics of it all something like 1.5 inches of HG vs 3.0. apples/oranges. the result is that a 650 cfm carb flows more than a 650 cfm TB or 670 for that matter. i thought ourr 670 cfm TB is equivalent to about a 600 cmf carb on net flow?

 

People will say lots of different things, but I talked with Holley directly and all of the 2 barrel tbi's are flowed at 3 hg.

 

Hmmm. now if someone has a 600 cfm carb laying around they could measure the venturies and do the math and determine what cross section measures up. my GM 7.4 L TB is 2 inches diameter or a net of 3.14 x 2 TB's or 6.20 square inches. i wonder what the 600 cfm carbs spec out at? would this be a fair comparison ? disregard the pod on top of TB for the sake of argument.

 

People always seem to get hung up on airflow even though the evedence shows otherwise that the flow is at least adiquate for high to mid 12's with a larger TBI.

 

What is it that keeps people from running high to mid 12's then with TBI cars? It is rare to see N/A TBI cars in the 12's, even with heads/cam/exhaust, and any idiot can do it with ease with PFI...Is the reason 2 vs 8 injectors, wet vs dry manifold?
Note: not trying to say any induction is better than the other, im just trying to see what the limiting factor of TBI is.

 

limiting fator is believed to be fuel for 2 barrel. BUT that is overcome with Holley 700/900 cfm unit and 4 injectors.

 

The primary reason you dont see more cars in the 12's may just be money, lack of knowledge, and inability to tune the system. While you can get away with some stuff with other induction systems, the tbi ecm sucks in stock form. At the very least you need to tune it or no matter how much money you spend.

Alot of those guys (some people actually do take the time to do it right) that run 12's, 11's and 10's with mpfi have very very thick wallets. Throw enough money at something and use enough nice parts and itll go fast. The only thing I have in my pockets usually is just alot of lint. I cant do much with pocket lint. Hell, I can hardly even scrape together enough cash to finish rebuilding my trans. If I had money I could probably put together something decent, but I have none at the moment.

 

So have I and they said 1.5"/Hg

 

Really, the man I spoke with at Holley about a year ago said everything 2 barrel was flowed at 3"/Hg. I have also spoken with turbo city which confirms this, which makes it hard for me to believe that those ratings are at 1.5"/Hg.

 

I read in a book (some book about Holley carbs) that they flow them at 1.5"/Hg, then posted it here. Someone questioned it but I paid no mind to them.

Later on (after my car got busted up) I bought a '71 Camaro and was thinking of transfering the TBI to it. I called them to find out for sure and they told me 1.5"/Hg.

Their reasoning is because with the diff between 2 and 4 barrel carbs, there are twice as many venturies in a 4 barrel. In an attempt to simulate/compensate what the engine will do with twice as many venturies, they (the industry) started to flow 4 barrel carbs at 1.5"/Hg in order to get the proper boosters, or something like that.

Since a TB has no venturies, just "bores", there is no reason to have to do that.

 

Hmmm, interesting info AJ. Looks like I will have to do some more reearch and talk to some more people to find out the truth.

 

what is difference between venturi and bore?