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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. Thanks
 

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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 …
 

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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
 

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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.
 

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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
 

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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
 
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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
 

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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.
 

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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.
Its the IAC issues aftermarket TB's have. Not necessarily initial idle...but idle issues when AC, PS is in use at a stop.

Aftermarket TB's don't have provision for IAC passage. It's more of a issue with camed engines

the crack the TB open some then slot the holes on the TPS to clock it back is one way of getting the IAC counts back in line
 

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Its the IAC issues aftermarket TB's have. Not necessarily initial idle...but idle issues when AC, PS is in use at a stop.

Aftermarket TB's don't have provision for IAC passage. It's more of a issue with camed engines

the crack the TB open some then slot the holes on the TPS to clock it back is one way of getting the IAC counts back in line
The Holley TB 112-509 has the IAC passages very similar to the stock TB.
And works well with my cammed 383. No idle issues with A/C and PS in use at a stop.

My IAC counts stay around 50 at idle when at operating temperature. No problems noted so far using my original IAC on the Holley TB. Yes the IAC counts are a little on the high side(Normal range is 20-50), but why mess with something that works?

I have the Holley 112-508 TB

YMMV
 

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The Holley TB 112-509 has the IAC passages very similar to the stock TB.
And works well with my cammed 383. No idle issues with A/C and PS in use at a stop.

My IAC counts stay around 50 at idle when at operating temperature. No problems noted so far using my original IAC on the Holley TB. Yes the IAC counts are a little on the high side(Normal range is 20-50), but why mess with something that works?

I have the Holley 112-508 TB

YMMV
Good your works...I didn't see the IAC air inlet/passage on the Holly like the stock TB

It has the hole on the lower part between blades that goes into where a stock IAC passage is?

IAC @ 50 at idle likely OK as long as IAC never pegs out with AC/PS loads. 30-35 (32) is stock

The Holly instructions do note to verify TPS VDC, to maintain proper tranny shift point & line pressure

"INSTALLATION:
1. Check and record the voltage of the throttle position sensor. Using a paper clip or pushpin, find the output on the TPS (Blue wire—5 volts).
7. Remove the throttle position sensor from the throttle body. Install the throttle position sensor on the new throttle body. Use the existing screws. To ensure proper operation of the new throttle body, you may need to adjust the throttle position sensor to the original voltage that was on the stock throttle body. The OEM is not adjustable. You may have to slot the TPS to properly adjust with a cordless drill and bit. "


the above TPS adjustments are typical of when you need to crack open blades to achieve correct IAC counts and in doing so that changes TPS VDC which can be corrected by slotting then rotating the TPS. TPS wants .67 VDC with blades closed and 4.5 VDC full open as otherwise tranny shift points and line pressure are affected
 

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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!
 

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Good your works...I didn't see the IAC air inlet/passage on the Holly like the stock TB

It has the hole on the lower part between blades that goes into where a stock IAC passage is?

IAC @ 50 at idle likely OK as long as IAC never pegs out with AC/PS loads. 30-35 (32) is stock

The Holly instructions do note to verify TPS VDC, to maintain proper tranny shift point & line pressure

"INSTALLATION:
1. Check and record the voltage of the throttle position sensor. Using a paper clip or pushpin, find the output on the TPS (Blue wire—5 volts).
7. Remove the throttle position sensor from the throttle body. Install the throttle position sensor on the new throttle body. Use the existing screws. To ensure proper operation of the new throttle body, you may need to adjust the throttle position sensor to the original voltage that was on the stock throttle body. The OEM is not adjustable. You may have to slot the TPS to properly adjust with a cordless drill and bit. "


the above TPS adjustments are typical of when you need to crack open blades to achieve correct IAC counts and in doing so that changes TPS VDC which can be corrected by slotting then rotating the TPS. TPS wants .67 VDC with blades closed and 4.5 VDC full open as otherwise tranny shift points and line pressure are affected
I checked my IAC counts when idling(in park) at operating temperature: 37
IAC counts idling in gear: ~50
 

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