tbfirebird

was wondering how much more power from the aftermarket tbi from holley it says 42% more flow has anybody tries it.

tbfirebird

somebody had to??????????????

AUTOGON350

iTrader: (8)

I have seen some real impressive cars with that 670TB and custom proms (300hp range) so I know it can be done.
I wouldnt expect a miracle from it If you built a real wild motor but its better than the 1-11/16 bore one that is stock If you have mods done.
The holley one is real expensive.
I picked up a 670 for $100 on ebay. It was the stock GM big block truck TB Check junk yards. Had to modify the mount for the linkage a bit but it worked great

I also tried boring a stock small TB out to almost 2inch like the holley and it works great compared to before.
Just the other day I read on a board that someone bored one out way over 2 inches and used hunts tomato paste cans to sleeve the casting for the throttle bores so If you have access to a machine shop or know anyone who does I hear that works.
I am going to try that soon on a junkyard throttle body and see how it works. $17 beats $250 for the holley

Hope that kinda answers some of your question

BronYrAur

iTrader: (1)

If you have a fairly mild 305 or even 350 the Holley unit really isn't necessary you'd be better off saving the money and using it on something else to get some real power. The Holley 670 is overkill for a 305 because if you're not making some huge power you're going to want to change out the injectors anyway because they're too big for a mildly built engine. You could just get the throttle body and put your stock injector pod on it so you have the 2" bores but your money is better spent elsewhere.

Fredless

Can you do this with a stock manifold or Edelbrock performer?

BronYrAur

iTrader: (1)

Both of those manifolds only have the 1 11/16" bores so the 2" bored TB would be a waste if it had to go down to 1 11/16 when going into the manifold. I'd say if you want to do that the best way to go would be to get an aftermarket single plane carb manifold and a TBI adapter with 2" bores.

Fredless

Hood clearance issue? I've got an open air 14x2 K&N and a 14x3 would not fit.

BronYrAur

iTrader: (1)

I wouldn't think you'd have a clearance issue with a 14x2. Make sure you get a shorter style manifold then, is this a stock 305 tbi you have, how did a 14x3 not clear the hood?

Fredless

Well, when I closed the hood it was hard to and the back end pushed up a bit when I forced it shut. I've got a Mr.Gasket open air thing but I threw out the paper crap that it came with and bought a 14x2. When i close the hood and peek up it when I do, it looks like the hood carpet sits on the top of the chrome of this one..

BronYrAur

iTrader: (1)

Did you get a non-drop base aircleaner or a drop base. You're going to want a non-drop base and if you have that you need to remove the spacer ring between the TB and the air cleaner. Did you remove this ring?

Also, you can find a lot of answers to similar questions like these in the TBI board just do a search.

Fredless

Its a small piece of cardboard.. That shouldn't make much difference. And I have no clue what the difference is. The stock air cleaner was lower than what I have now somehow, but the K&N I had for that P.O.S. is the same height I believe, just smaller in circumference.

Z28 Boy

depends on the rest of the engine setup, and injectors, etc.

could be a little...could be a lot.


-brian

fb305svs

I tend to disagree with the statement that 670 is over kill for the 305 or mild 350.

In theory, your claims are more than justified- however, i have a 305, ad a holley 670 carb, and it makes much more power than the 550 i had on it previously. The 550 being mechanical 2ndaries, the 670 vacum. The stock TB is only somewhere around 430 cfm flow rating- in my personal opinion, after an exhaust, i think that would be the next thing i do!

Just another opinion from the peanut gallery!

Z28 Boy

i agree 110%.

-brian

Dewey316

the only problem i see in your logic is this.

on TBI where is the BIGGEST restriction ,and what does the engine NEED. no matter how large of a throttle body you put on, if the heads/cam combo and intake manifold, only aloow 400 CFM of air into the engine, then you only need 400CFM of air going through the throttle body. i mean i could put a 2000CFM throtle body on, but i probably won't see nay more gain than i would with a 670CFM TB. and i also may see the same gain from just cleaning up the factory TB so that the airflow is not so turbulent.

fb305svs

Well take my motor for example- stock heads, with smaller valves (LG4 heads, 186 intake) and a stock intake made more power with the bigger carb, and intresting thing is, the carb was the only change, and both the a/f for both setups was more or less exactly the same.

Maybe we are comparing apples and oranges, but i still think there would be a lot to gain- and it would be something you likely will do later on down the road. The stock heads and intake as a whole flow a lot more than 400cfm as well.

in your defence, we made 430 hp out of a 350 with a track mandated 2 barrel 500cfm carb and a aluminum 2 barrel oem intake. just keep in mind that about 5000 dollars worth of labor and dyno time went into designing the cam to work with that combo (and give us the power where we needed it for the track)

fb305svs

.

Dewey316

i never said it wouldn't make more power, i really don't know what the BIGGEST restriction is. maybe it is the 400cfm TB, maybe it isn't. the point is, that bigger isn't always better. my first thought is that you are better off doing some FREE mods to the factory TB, and spending that TB money on something like free flowing exaust. or a cam. you will most likely see bigger HP gains from those.

fb305svs

Agreed- i posted my sig so you could see what i have done


no doubt, on a TBI, here's ,my opinion of the list of biggest restrictions in the motor system. List goes from biggest stock restriction to least. (although in the end they are all a restriction)

1) Exhuast - full exhuast a must.

2) TBI throttle body... with the experiances i have had- the intake/heads can handle much more than a 400cfm TB, although likely a 670 is pushing it for stock pieces.

3) Cam... yes cam, becuase the intakes aren't as bad as you might think-

4) heads/intake - both of these together because its pointless to do either with out the either.

In all reality- the heads/cam and intake should all be changed at the same time- but with a cam change, more power CAN be eaked out of the stock heads and intake package.

Like its been mentioned, the stock TB can be much improved, and with good results, but later down the road, just replacing it becomes a seemingly better option.

BronYrAur

iTrader: (1)

Yeah I see what you guys are saying, don't get me wrong I wasn't saying that the 670 would be bad because it wouldn't and yeah I'm sure it would give some power, but if he has a fairly stock LO3 that TBI's came on, money is better spent on full exhaust with headers, heads, cam, and intake. The tbi is different from a carb because if you need more flow you can just add bigger injectors to it, so I would say that the 2" bore TB is not necessary until you do some more stuff to the engine and once you're going to buy a new intake then buy a 2" intake and get the 2" throttle body at the same time.

AUTOGON350

iTrader: (8)

Dont forget that the 2barrel throttle bodies are rated at 3.0 inHg pressure drop and 4 barrel carbs are rated at 1.5inHg pressure drop.
The flow throught a 670 TBI is a lot less probably a bit more than half of the flow through a 670 four barrel carb.

with the money you could save by not purchasing the 670 holley a person could by a dual quad manifold and run two of the smaller throttle bodies or some other cool custom setup.
The holley 670 just does not seem worth it to me.

Then again I have to sit up to see over my cowl hood and can barely hear my passenger talking over my exhaust so my Idea of everyday driver is a little different than some peoples.

fb305svs

amen brotha- same here hahaha