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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old April 16th, 2017, 02:26 AM
wcstory wcstory is offline
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Default Question about switching to a Holley 500

I purchased a 4412s Holley 500 to make my 305e breathe a little better. I also have a 70's style gas pedal assembly and new throttle cable to replace the solid linkage.

What throttle bracket do I need to install the 500cfm with a newer style cable?

I will be installing a 700r4 next step once the Lokar shifter and lockup harness come in.
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Old April 16th, 2017, 02:19 PM
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Quigley Quigley is offline
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Default Re: Question about switching to a Holley 500

On my 66 with a Powerflow the stock throttle linkage worked perfect on the Holley. Choke cable was too short, because the hookup was on the other side of carb. Dave
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Old April 16th, 2017, 03:29 PM
wcstory wcstory is offline
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Default Re: Question about switching to a Holley 500

I decided to read the documentation that came with the 4412 Holley

Holley 20-95 Throttle Cable Bracket

Holley 20-89 Return Springs


From the 60-66 GMC site

Mr. Gasket Adapter #720-1937.

XRP 700106 Size 6 to 7/8-20 Holley Carburetor Adapter

XRP 239006 Size 6 90 Degree Push-On Hose End

I think I may have the manifold machined flat and weld a Holley base plate onto it.
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Old April 16th, 2017, 03:57 PM
bigblockv6 bigblockv6 is online now
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Default Re: Question about switching to a Holley 500

I think I may have the manifold machined flat and weld a Holley base plate onto it.[/QUOTE]

It wouldn't be necessary to go through all that, what I have done is opened up base on the manifold with a die grinder to match the throttle plate bores of the Holley as well as open the bores of the adapter. You don't want the carb sitting too low on the manifold. Many GMC V6 engine used spacers between the carb & manifold, this helped with velocity. Some 351C and many 379 engines in Medium duty trucks actually came with a 8 to 10 inch tunnel ram
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Old April 16th, 2017, 04:32 PM
wcstory wcstory is offline
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Default Re: Question about switching to a Holley 500

Do the 305 manifolds normally have the carb sitting at an angle? The one I picked up to modify definitely does.
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Old April 16th, 2017, 05:14 PM
Culver Adams Culver Adams is online now
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Default Re: Question about switching to a Holley 500

Hello Wcstory,

Regarding angle: the engine is designed to sit at a nose-high angle. The angle you see at the carby is to keep the carby level.

Regards and Hope that helps,

Culver
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Old April 16th, 2017, 05:45 PM
bigblockv6 bigblockv6 is online now
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Default Re: Question about switching to a Holley 500

Quote:
Originally Posted by wcstory View Post
Do the 305 manifolds normally have the carb sitting at an angle? The one I picked up to modify definitely does.
The angle on the manifold is typical of most all carbureted GM V6 & V8 engines of the 60's & 70's
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