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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old January 2nd, 2022, 02:33 AM
mcmyket mcmyket is offline
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Default Holley Sniper 2300

Hello,

I have a 64 GMC with a 305 v6 that I've recently purchased and was considering a Holley Sniper 2300 fuel injection setup for it. I see there was a thread in 2020 talking about it, but I don't see where anyone has completed an installation. Has this setup or any other fuel injection system worked for anyone yet.

Thanks!

Mike
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  #2  
Old March 8th, 2022, 04:49 PM
Gwhizzard Gwhizzard is offline
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Default Re: Holley Sniper 2300

the only thing that doesn't help and might throw it off is the intake being it does not really distribute fuel equally. but have seen post on the 67-72 forum that showed a 61 suburban with 88 gm tbi unit on it. so id say go for it and see what happens lol ive looked into it as well. but haven't pulled trigger et on anything due to other projects inline first.
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  #3  
Old March 8th, 2022, 05:56 PM
Prowbar Prowbar is offline
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Default Re: Holley Sniper 2300

Quote:
Originally Posted by Gwhizzard View Post
the only thing that doesn't help and might throw it off is the intake being it does not really distribute fuel equally.
How do you know it doesn't distribute the air-fuel mixture properly?

@Mike: I for one, don't know anyone that has one of these V6's on (Holley) EFI, except for the Chevy TBI system. I'd be very interested though if you decide to try!
But I believe that port injection is superior to these TBI units though.

Last edited by Prowbar; March 8th, 2022 at 06:06 PM.
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  #4  
Old March 9th, 2022, 02:58 PM
James James is offline
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Default Re: Holley Sniper 2300

Quote:
Originally Posted by Prowbar View Post
How do you know it doesn't distribute the air-fuel mixture properly?

@Mike: I for one, don't know anyone that has one of these V6's on (Holley) EFI, except for the Chevy TBI system. I'd be very interested though if you decide to try!
But I believe that port injection is superior to these TBI units though.
I have flow tested the intake manifold and found with the stock two barrel carburetor the flow is about equal. With the Holley two barrel the center runner flow is very low. This is why the magnum intake has no divider between runner 1-3 and 4-6. If you look at the top of the manifold you will see the center runner makes a 90° turn, air don't like to make sharp turn so it restrict the air flow.

In my opinion, port injection is superior but with these engines a TBI would be better base on the intake limitation.

Last edited by James; March 9th, 2022 at 03:28 PM.
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  #5  
Old March 9th, 2022, 06:09 PM
Gwhizzard Gwhizzard is offline
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Default Re: Holley Sniper 2300

Prowbar.. I personally have not flow tested or tried to improve the intake yet... but i have read alot of the 4 barrel carb mods and the one thing they do is soften the turns up inside of the intake to make it smoother transition. There are a few on 67-72 and jalopy journal of people modding these intakes. if they are still out there.
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  #6  
Old March 9th, 2022, 06:37 PM
James James is offline
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Default Re: Holley Sniper 2300

Quote:
Originally Posted by Gwhizzard View Post
Prowbar.. I personally have not flow tested or tried to improve the intake yet... but i have read alot of the 4 barrel carb mods and the one thing they do is soften the turns up inside of the intake to make it smoother transition. There are a few on 67-72 and jalopy journal of people modding these intakes. if they are still out there.
This is what I had done to my intake ports and the carb flange on the intake manifold:

On the carb flange picture, I was almost done, just wanted to show how much metal was removed.

On the ports, I left a small section of the runner divider to hold the gasket in place and so I would be able to install any small port heads without issue. Did not make the port any larger, just remove the divider.

This manifold now flow very well with the Holley 2 barrels.

It took a lot of work and patient to get it there. Engine run better too. Want to pull harder.
Attached Images
File Type: jpg Carb flang mods in progress.jpg (4.81 MB, Multiple views, 9 clicks)
File Type: jpg Intake ports with most of runner divider removed.jpg (4.39 MB, Multiple views, 9 clicks)
File Type: jpg Flow testing manifold with carb.jpg (4.32 MB, Multiple views, 9 clicks)
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  #7  
Old March 10th, 2022, 11:41 AM
Prowbar Prowbar is offline
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Default Re: Holley Sniper 2300

Looks excellent. Regarding the Holley conversion, this is something that one needs to pay attention to.

Quite surprised the intake does distribute the flow equally. However, with the sonic pulses that might be different. The only way to test that would be to make a spacer plate that mounts between the cylinder head and exhaust manifold and has 3 O2 sensors, connected to each runner, to measure the A/F ratio of each cylinder.

Another point regarding the A/F ratio of each cyl. would be the PCV valves tapping into runners 3 and 5 but not in runner 1. This should affect the A/F of 3 and 5 to some degree. Especially with a worn engine.

A centralized PCV would be better I think.
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  #8  
Old March 10th, 2022, 01:51 PM
Gwhizzard Gwhizzard is offline
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Default Re: Holley Sniper 2300

Nice setup. I like what you did with it..
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  #9  
Old March 10th, 2022, 02:52 PM
James James is offline
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Default Re: Holley Sniper 2300

Quote:
Originally Posted by Prowbar View Post
Another point regarding the A/F ratio of each cyl. would be the PCV valves tapping into runners 3 and 5 but not in runner 1. This should affect the A/F of 3 and 5 to some degree. Especially with a worn engine.

A centralized PCV would be better I think.
The PCV valves will lean out cylinder 1-3 and 4-6. It also effect the flow through the runners, base on my flow bench numbers. Blocking the passage between the ports will change the flow rate. When I get done with modifying my spare heads, it will not have the internal PCV valves only an external one.
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  #10  
Old March 10th, 2022, 05:22 PM
Prowbar Prowbar is offline
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Default Re: Holley Sniper 2300

You're correct regarding the ports. I'm still thinking about the PCV system conversion. On my IMPCO propane mixer air cleaner, I have a way to attach a PCV hose. Now to tap into the engine. Either convert the filter canister on the back of the block or use one of the valve covers. I don't like drilling holes in original parts, possibly a custom oil fill cap with a PCV hose fitting in the center.

What are your thoughts?
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