Well my stock throttle body is junk because it leaks fuel out of the in line fitting off the back of the TB, so i decided instead of going back to stock why not upgrade. So i bought a Holley 670CFM TB Unit off a co worker of mine whos cuzin had it on his plow truck. It has 2" bore diameters and is an OEM exact fit. It was manufactured for a gm car or truck with electronic kickdown for the transmission but had a hole for a stud in case yours was mechanical. So i had to cut the top sutd off and punch it out to put a new one in made to face towards the TB unit because it faced away, then install another new stub below that one facing out. Now i heard stock TB units only have about 500 or so CFM's if they are not mistaken. But what kinds of gains should i notice with just changing them over? more top end toruqe or more low end? I do and will need to do some tuning because it also has an ajustable Fuel Pressure Regulator on the back side that can be turned up to 15LBS. But i hear 7-8LBS is good for my 305???? It sounds all cammed out and runs real rich even with the fuel pressure all the way out. So im guessing i need a bigger intake manifold to distribute the fuel better, maybe a high rise??? Its also still leaking fuel out the in line fitting off the back but i belive its because the new fuel lines are too lone and are bent wrong putting pressure on the backside because they r crammed in there. Any reccomendations for that? heres a link to the TB unit i have now, and if anyone has any suggestions to get the most out of this TB let me know. By the way i bought it used and paid 75 bucks for it.
http://www.holley.com/types/Direct%20Replacement.asp
http://www.holley.com/502-5.asp

Mine is on the right. Let me know thanks.

 

TA, on an 305 with stock heads and cam, the stock TBI unit, which flows around 490cfm, gives plenty enough air flow, and going to a unit with more flow without goosing the heads and cam will typically make you go slower.

This is because for a given engine size and useable RPM range there is an optimum size for the TBI unit to keep the incoming air and fuel in the best velocity range, and by going too big the incoming air slows down more as it comes thru the TBI unit and doesn't fill the cylinders as efficiently.

At least that's what the "on paper" approach says, since you have the Holley unit installed I'd fix the leaks, get it tuned in and see how fast you go with it.

If you slow down have the stock unit fixed or find a replacement for it.

Paul T.

 

i also have a holley tbi but i didnt notice any difference because i dont know how to tune yet. i took the stock tbi and installed it back.

 

What kind of injectors does it have? Are they the kind with the hemispherical tops (the ones in the linked photos), or the small style delphi units with the 'RP' on the top of the weather pack connector?

The richness may be due to the injector flowrate, or leaking injectors, depending on what type it came with.

 

it has the kind in the picture, the stock connectors that go on top of the stock TB are too spaced apart and the prongs on the holley are closer together so i had to cut the wires and wire in the new ones. I plan on buying new heads and cam plus intake manifold but i figured id pick up the TB unit while i could since it was cheap. The injectors dont leak after you turn the key off i just need to turn the fuel pressure way down. But i plan on also having the whole engine remaned so when that time comes im going to have the new heads and intake and just everything i have so far installed. I know its been discussed over and over but what type of heads are inexspensive but also good to use on a TBI engine? Ive looked over many types dressed and not dressed and i just cant seem the right type. If anyone has any suggestions from their own personal 305 build ups lmk. Thanks all for the info so far.

 

If someone could post a picture of their TB unit and linkages hooked up i would appreciate it. Im not sure if i have mine hooked back up right. I think it goes kicdown cable on top, then cruise control in middle then of coarse throttle linkage on bottom.(i know i have that one hooked up right) I also need to run smaller nuts on the back of the new studs as they are causing binding in the cables.

 

check out World. They make a specific iron head for 305. Vortec is a good choice but the manifold has to be Vortec as well.

 

I know when going votec that you have to switch the manifold as well. i will check out World later tonite. thanks