Was thinking about getting at Holley 58mm throttle body it's cheap is it worth it? And should it just bolt up to a STOCK INTAKE. I have ARF HEADS, 3O LBS holley injectors, roller rockers, bbk headers, upgraded torque converter, cold air intake, mild cam, 255lph fuel pump, complete rebuilt bottom end, stroke 383. F body mass air flow. Msd wires and opti, Ngk plugs.
Will the throttle body make any difference?

Did you forget to mention 'headers', 'hi-flow catalytic converters', and/or 'full 2.50" catback exhaust system'?
Because without those things, a 58mm throttle body will not make enough difference to justify the expense.

Besides which you're better off having your throttle body rebored to 52mm, safer than buying an aftermarket throttlebody of either 52mm or 58mm. Also, very few LT1 engines, even 383s, NEED 58mm throttle bodies.
I used to know the name of ISSF guy who did this years ago …

 

It has headers ,straight pipe no cats. 52mm? Does that bolt up with no issue?

 

A 58mm throttle body will not help you unless your intake has also been bored for the larger size.
For my 383, I had the intake ported by Lloyd Elliott to be able to use the 58mm Holley. I tried running the stock b-body maf and it was flatlining. I have since installed a f-body maf and converted to running speed density.

I am not sure if I need the 58mm throttle body, but I wanted as much flow as possible. I have the try-y headers and a 2 1/2" cat back system with high flow cats. I will be removing the cats soon with Clear Image export pipes in ceramic coated stainless.

YMMV

 

I probably go with 52mm

 

Greater "potential" flow does not translate to more flow for a couple reasons ,possibly more. It only flows what intake can draw. As the hole gets bigger ,the flow decreases in speed. Intake air speed is what helps fill cylinders.

 

Most people don't make enough HP to justify a 58mm. And many aftermarket TB's just don't work right. In most instances to like 450hp the stock TB is fine

 

Stock 48mm and making approx 400rwhp/400tq. Doesn't seem like the laundry list of idle quality issues the aftermarket ones have are worth chasing. I do think I could probably gain something having my factory bored out to 52mm at some point.

-Brian

 

OP

you will need to pull your intake and have it machined for 58. Then you will need a PCM re-tune or tranny failure will soon follow. Then you will need scan software capable of reading IAC counts and then either adjust throttle blades out further (never a good thing) or do the "drill" mod to get it to idle right....and all that to get little to nothing in performance gain with your set up

"if" you can find a source to bore a stock to 52...that is plug & play but you still need a PCM re-tune to adjust tranny line pressure

 

I did not have to do anything for the idle using the the Holley 58mm throttle body. I did alter (+10%) the transmission line pressures for the TB change.

 

Ballss,
The IAC counts never peg out under any conditions. So I am good there.

As to the TPS adjustment, I did that procedure and slotted the TPS to adjust to have proper voltage range.
One thing I did not like about the Holley TB: It will go past 4.5 volts at WOT. I had to create a bracket to stop the blades from going too far. Once past the voltage limit, the transmission goes into limp mode and did not recover until I removed power from the PCM. Since then, no problems. I figured that I would have to make changes, but that is what we do for progress.

A little shade tree mechanics goes a long way!