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Old 03-20-2018, 02:00 PM   #51
54Caddy
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Re: Install thread- Holley EFI Sniper on '72 402 big block

My concerns are really for the fuel pump having to draw the fuel up the stock line in sending unit then down to pump. Also as stated with a carburetor you have fuel bowls which are little reservoirs for fuel. With EFI you do not have that, A GM TBI unit can’t compare it only requires 15 psi not the 60 the efi requires. I’ve read a few people wanting to route the same way you are and landed up putting bungs on bottom of tank.
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Old 05-13-2018, 02:06 PM   #52
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Re: Install thread- Holley EFI Sniper on '72 402 big block

A pause in progress since finding the crack in the intake manifold. Got the intake off and the heads cleaned up, in anticipating of installing a replacement intake manifold. Then, everything back together, add coolant, start er up, and pick up where I left off.



Clean left. Dirty right.
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Old 05-13-2018, 07:20 PM   #53
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Re: Install thread- Holley EFI Sniper on '72 402 big block

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Old 05-13-2018, 11:30 PM   #54
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Re: Install thread- Holley EFI Sniper on '72 402 big block

I fitted the Sniper EFI to the 396 in my truck and picked up a bunch of low down and midrange torque. The throttle response is way better. But the gas pedal was so touchy I had to make a small extension for the linkage where the rod hooks up.
Yours appears to be a cable so you may not have the same issue.
Overall Iím very happy with mine.
Hereís a pic of the extension
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Old 05-14-2018, 12:09 PM   #55
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Cool! I'm at almost the same point, hooked up the linkage on my Sniper last night.

I'm excited to see how it drives. I had a Q-Jet on an oval port manifold on roval port heads and I've also put the port-matched intake back on so that should help as well.

I'm not doing computer timing control, did you?

Here's the fuel lines I bent up yesterday!
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Old 05-14-2018, 05:12 PM   #56
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Quote:
Originally Posted by davepl View Post
Cool! I'm at almost the same point, hooked up the linkage on my Sniper last night.

I'm excited to see how it drives. I had a Q-Jet on an oval port manifold on roval port heads and I've also put the port-matched intake back on so that should help as well.

I'm not doing computer timing control, did you?

Here's the fuel lines I bent up yesterday!
Nice work on those fuel lines.
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Old 05-14-2018, 05:58 PM   #57
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Those lines look great. No timing control on my setup.
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Old 05-15-2018, 09:54 AM   #58
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Re: Install thread- Holley EFI Sniper on '72 402 big block

As long as none of my lines leak (this is my first time ever doing stainless with AN fittings) I think it'll be a killer setup. Like you, I'm going to forego timing control at least at first as well, maybe do that as a second project, but I haven't heard great things yet about it.

I haven't checked the geometry yet, I have solid pedal linkage as well. I had to drill the hole larger to accommodate the linkage though. Once installed with plastic bushings it was nice and solid, but I'll have to wait and see if I have the same sensitive pedal that you did.
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Old 05-15-2018, 11:17 AM   #59
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Re: Install thread- Holley EFI Sniper on '72 402 big block

I'm not having the computer control timing. As I understand it, I have to buy a specific distributor that has a plug in for the Sniper system. I've watched the video of the setup. It's out of my level of experience, so I'll likely get some help if I go that route in the future. I like the idea of combining EFI plus timing control to get max performance, all automatically with a computer.
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Old 05-15-2018, 11:44 AM   #60
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Assuming your distributor is well set up for your engine, I don't think there's much performance advantage to be had. But it can in theory help smooth the idle by adjusting individual spark pulses. That's the only feature I'd actually like.

They give you a coil driver so that you don't have to run a full ignition box, that's kind of interesting.

I have an MSD dual sync with the same purple and green wires, but I'm not sure if I can make it work with the Holley and am a little scared of biting off more than I can chew in trying to do the install with a non-supported third party pickup!
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Old 05-15-2018, 05:38 PM   #61
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Re: Install thread- Holley EFI Sniper on '72 402 big block

A lot of people have had trouble getting their msd distributors to play nice with the timing control function. I think the Holley dual sync is probably the best option if you want to use timing control and of course more expensive than msd. For me, not worth it at this stage.
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Old 05-17-2018, 01:58 PM   #62
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Got mine all up and running (not a truck, but I'll try to stick a photo in anyway). The throttle is SUPER touchy, as you say. I'll order a Holley throttle extension or make one, I guess.

Was yours better with the extension? With a deep four speed a 4.10 gears it's a little touchy to drive! By which I mean "almost impossible to drive safely" as it is. They really ought to include that extension if they're all like that.
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Old 05-17-2018, 06:20 PM   #63
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Re: Install thread- Holley EFI Sniper on '72 402 big block

I'm curious for those who have installed a Holley Sniper kit and have used the supplied Holley electric in-line fuel pump, is the electric pump noisy?

Thanks,
Miles
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Old 05-17-2018, 06:20 PM   #64
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Sorry about the thread hijack Ekliptix but I figure this is useful info.
davepl, the throttle extension made a big difference for me. But Holley also has a progressive linkage available which you can adjust the snipers software for.
It reportedly makes a big difference.
Hereís the info on it.
https://forums.holley.com/showthread...I-WAAAY-Better
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Old 05-18-2018, 10:37 AM   #65
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Re: Install thread- Holley EFI Sniper on '72 402 big block

I'm not using the Holley pump, but a Tanks Inc module which has a factory style pump inside the tank. You can hear it a little.

Yesterday once the fuel got hot after 30 minutes or so of driving it was noticeably louder.

Much quieter in tank than the old Holley blue or black pmp hanging off the frame though!
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Old 05-18-2018, 11:15 AM   #66
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Re: Install thread- Holley EFI Sniper on '72 402 big block

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Old 05-18-2018, 07:39 PM   #67
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Re: Install thread- Holley EFI Sniper on '72 402 big block

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Originally Posted by davepl View Post
Cool! I'm at almost the same point, hooked up the linkage on my Sniper last night.

I'm excited to see how it drives. I had a Q-Jet on an oval port manifold on roval port heads and I've also put the port-matched intake back on so that should help as well.

I'm not doing computer timing control, did you?

Here's the fuel lines I bent up yesterday!
That looks really nice. Is one of them a bypass/return line? I'd think you would have some vapor lock issues with such a long run above a hot engine.
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Old 05-19-2018, 04:28 PM   #68
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Yes, the passenger side port is the return line, so there's a constant high-speed flow of 60psi fuel past it at all times. When there's no draw from the engine, the pump is basically pumping full blast at all times circulating fuel, so it'll never sit in the lines.

It could over time heat up the fuel in the tank though! Now there's a 16' fuel line run that'll help cool it down but I might consider adding some insulation on the intake if I can make it kinda stock, thanks for the idea!
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Old 05-20-2018, 08:51 AM   #69
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Subscribed. Planning on this for Walt, when I get the 468 swapped in.
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Old 05-20-2018, 10:09 AM   #70
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Re: Install thread- Holley EFI Sniper on '72 402 big block

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Subscribed. Planning on this for Walt, when I get the 468 swapped in.
Ahem .. practice on mine ?
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Old 05-20-2018, 04:40 PM   #71
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Re: Install thread- Holley EFI Sniper on '72 402 big block

Never even considered a return system such as this heating up the fuel in the tank. This could explain some hot start issues I've been having!

-klb
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Old 05-20-2018, 06:57 PM   #72
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Re: Install thread- Holley EFI Sniper on '72 402 big block

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Ahem .. practice on mine ?
You buy it & I’ll come and help install it! . Sorry for the thread jack.
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Old 05-23-2018, 01:46 PM   #73
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Re: Install thread- Holley EFI Sniper on '72 402 big block

I hope to get it running again this weekend.

Cracked vs new


Ready to install the new intake.


Torqued to spec
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Old 05-24-2018, 08:07 AM   #74
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Re: Install thread- Holley EFI Sniper on '72 402 big block

I bet by now you can’t wait to get the truck out on the road.
Wise choice on the 4 hole spacer. I used an open one and had a very noticeable squeal on hard acceleration. I installed a 4 hole spacer and it’s totally gone.
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Old 05-24-2018, 10:50 AM   #75
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Re: Install thread- Holley EFI Sniper on '72 402 big block

For anyone following along, two things:

1) That "Notch" in the two-plane intake is important. If your intake is sealed all the way such that the two planes are totally separate, TBI EFI will not run well (or for some brands at all) because the MAP sensor is only on one of those sides. I can't tell if the old 4-hole was separate side to side, but the new one looks OK. The ZZ502 intake from Chevrolet has a notch too, but smaller.

2) Holley offers a linkage extension as well as progressive conversion linkage. I have ordered the progressive kit because otherwise it is VERY touchy. Consider that it opens all four barrels right off the start...
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