1968 Impala Repower Thread - Page 5 - Impala Tech
Engine General Engine Discussion.

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post #101 of 111 (permalink) Old 09-13-2019, 10:54 AM
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How has everything turned out? Did you get your rough idle fixed? I have a similar setup with a 502 and terminator EFI.
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post #102 of 111 (permalink) Old 09-13-2019, 08:02 PM Thread Starter
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The rear axle is set up and good to go, which was the last big step. I have had nothing but problems with the EFI and have sent it back to Holley again for repair. At this point, I do not recommend it. It is definitely not a reliability upgrade over a carburetor. I've only driven the car outside my neighborhood a half dozen times, and it's left me stranded twice already, once requiring a tow home. I want to believe, but my confidence in the system is seriously rattled and I'm not sure I'll ever be able to drive the car without fearing its getting ready to shut down due to some electronic gizmo in the EFI randomly deciding it wants to ruin my day.

I'm giving it one more chance and then I'll be scrapping the damn thing and going with a carburetor. If it was self - tuning like they say, there wouldn't be a Holley forum full of guys who can't figure out how to get their cars running right.

Attached are some pics - it's done at this point with the exception of the fuel delivery. Lessons learned:

1) EFI sucks. Nothing but a headache.
2) I had nothing but problems with the PTFE thread sealer as well. It leaked everywhere I used it. Coolant and oil. Replaced it with Teflon tape and haven't had any problems.
3) Retorque all fasteners after the first few times you drive the car.
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1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
68WASAGOODYEAR is offline  
post #103 of 111 (permalink) Old 09-17-2019, 04:09 PM
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Have you posted the problem on the Holley forum? I had a few bugs on the first setup, but a quick forum post and working with the person I bought it from solved the problem now. Sure I could and will tweak it some more when I can do a dyno tune, but I have zero regrets on spending the time and money on the EFI setup. I might even go the dual quad Sniper install this winter on a SBC update.
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post #104 of 111 (permalink) Old 09-17-2019, 07:48 PM Thread Starter
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I have posted it on the Sniper forum (same user name) and gotten some feedback, but nothing I hadn't already checked. I did hear back from Holley and they said they had been able to "recover" the ECU and that the unit had passed all their tests. They're shipping it back to me. So I'm back to square one in terms of troubleshooting the issue and preventing a recurrence.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #105 of 111 (permalink) Old 09-20-2019, 09:46 AM
 
 
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I finally got around to having my sniper unit installed on my 70. Been good so far. Only problem I have is that stiff toe in off idle. Not so bad at cruising speed. I did read through quite a few posts on the Holley forum that discuss this same problem as well as talking to a coworker who has this setup on his late 60s Mustang and early 80s cutlass.

Some of the posts talked about the linkage on the sniper being smaller than a typical carb. Holley has a bracket extender that is supposed to make that throttle more linear instead super stiff off idle. The coworker also mentioned that he put a different return spring so it isn't as stiff.

EDIT: Here is the link to the throttle lever extension
https://www.holley.com/products/fuel...BoCYvUQAvD_BwE


I only have about 50 miles on this new setup but haven't noticed anything out of the ordinary yet.

1970 Impala Custom coupe
400ci SBC

Last edited by FearlessAZ; 09-20-2019 at 08:09 PM.
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post #106 of 111 (permalink) Old 09-20-2019, 09:54 AM
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I have the other TB, but did install that linkage adapter on mine since it was super touchy at idle and with all the power it make start interesting. The new adapter did really help but it has the linkage rod hit the firewall now at the very end of the throttle travel. I"m taking a 1/4" max of WOT which isn't a big deal.

I might try a wire throttle compared to the linkage, anyone update theirs to a cable before?
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post #107 of 111 (permalink) Old 09-20-2019, 05:35 PM Thread Starter
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I did install the progressive link on mine. It's more or less required with a manual transmission, otherwise the drivability suffers. You also have to change a setting in the handheld to enable this and also remap the acceleration enrichment vs. TPS in the Sniper software to get the full effect of this. I'm reinstalling the sniper now...

I'm still using a throttle rod, just updated with heim joints on either end.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #108 of 111 (permalink) Old 09-30-2019, 09:51 AM Thread Starter
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I *think* I might have gotten all the bugs out of the EFI. Here are some final thoughts for anyone looking to do this as an upgrade:

1) Create a username and join the Holley Sniper forum
2) If you have a manual transmission, switch to the progressive linkage and perform the associated changes in the handheld (see forum for how-to)
3) Do not buy the Sniper master install kit. Do yourself a favor and get a seperate in-tank electric fuel pump. EFISystemPro.com.
4) You need a properly vented fuel tank. The fuel return line was enough to close the rollover vent I installed in my tank, which pressurized the tank and caused all sorts of weird issues with the EFI.
5) You will need a throttle return bracket and spring
6) Install an Innovate Motorsports (P/N HBX-1) bung extender/heat sink. This will prolong the life of the O2 sensor and prevent erroneous readings.
7) Keep the Sniper cables away from your spark plug wires. The Sniper is very susceptible to electronic interference. I used MSD plug wires with the insulation that minimizes interference as well as wrapped the Sniper cables in EMI tape and clipped them as far away from the plug and coil wires as I could.
8) Plan on spending an additional $500 or so having the Sniper properly tuned. This requires a dyno, laptop with software, and of course the know - how. I'm sure there is a vanilla 350 SBC out there that is just fine with the stock tune, but my engine required a full custom tune with fuel mapping, etc.
9) The Sniper only supports up to 800 CFM!!! This is not advertised anywhere that I could find. I heard this posted on the forum. The product literature says it supports up to 650 hp. This is not a deal breaker for me even though my 496 needs 870 CFM. I'm not racing the car; I'm just giving up some hp. If you need more, you need to look into the Terminator 950 or new dual quad Sniper set up they just released, which I'm sure is an absolute nightmare to get set up properly and is way more expensive.

I don't mean to dissuade anyone looking to do this mod. I'm sure I'll be happy with it in the long run. Just wanted to put this out there. It might have changed my mind.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #109 of 111 (permalink) Old 10-01-2019, 08:34 AM
 
 
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Garage
Under the Tech Specs for the Sniper, it states 800 CFM. The newer XFlow unit flows 900 CFM. The newer XFlow does start at like $1300 for just the TBI unit.

I know your build is completely different than mine. Can't imagine how much harder it is with the manual.

Did yours have the issue with a touchy toe in off idle? I installed that throttle lever extension and man, what a world of difference on the drivability. I debated that progressive linkage to help a bit with cruising but haven't had any issues yet.

Once I do heads, cam and rebuild on the 400, I will do a custom tune. I can't see myself doing that until a little farther down the road.

1970 Impala Custom coupe
400ci SBC
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post #110 of 111 (permalink) Old 10-01-2019, 08:47 AM Thread Starter
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Quote:
Originally Posted by FearlessAZ View Post
Under the Tech Specs for the Sniper, it states 800 CFM. The newer XFlow unit flows 900 CFM. The newer XFlow does start at like $1300 for just the TBI unit.

I know your build is completely different than mine. Can't imagine how much harder it is with the manual.

Did yours have the issue with a touchy toe in off idle? I installed that throttle lever extension and man, what a world of difference on the drivability. I debated that progressive linkage to help a bit with cruising but haven't had any issues yet.

Once I do heads, cam and rebuild on the 400, I will do a custom tune. I can't see myself doing that until a little farther down the road.
You are correct about the 800 cfm being shown in the tech specs. I just wish they advertised that a little more up front - they only really talk about it supporting 650 hp. My engine makes 585 hp, so I didn't give it a second thought. As it turns out, I only need 830 cfm for my engine (not 870 as previously shown), so I'm OK with just 800.

The car was almost undriveable with the 1:1 linkage and manual transmission. The gas pedal was very stiff. In first gear I'd be trying to ease into the throttle, but the pedal just wouldn't move. Since I was slowing down, the car would then start to buck like it was going to stall so I would give the pedal more pressure and then BAM the tires would break loose. Engaging the clutch was a nightmare too. The progressive linkage really helped and I might try the extension as well.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
68WASAGOODYEAR is offline  
post #111 of 111 (permalink) Old 10-01-2019, 09:44 AM
 
 
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Garage
I think they realized this in the description cause if you look at the XFlows on Holley's website, it is right in the short description now before clicking on a specific one. You are right though that it should be stated better rather than buried in tech specs.

The extension makes it way more linear instead of hard toe in. I was reading around the Sniper forum (SO MUCH KNOWLEDGE) and they said the difference is the Sniper throttle linkage is smaller than a standard carb like a normal Holley or Edelbrock. It basically lifts the throttle linkage up a bit. Probably geometry too. Mine was doing kinda similar to what you described except for the stalling part. I would be driving though the neighborhood or stopped at a light and would try to ease in to the throttle but that super stiffness. Made it so I was kind of reving at other cars or reving in front of houses with super minimal effort. With that little extension, it felt like normal again.

My coworker has the Sniper set up on him late 60s Mustang and early 80s Cutlass and he has the same issue with both. He tried this extension on the Cutlass as a test subject for us and said it solved this same issue. Think he already ordered the same part for his Mustang. These were all auto vehicles so I would hope this helps a manual as well.

Really wish Holley would note this somewhere in their instructions or mention the possible issue. Shouldn't have to dig around a forum for that. I mean, it is a Holley part after all.

1970 Impala Custom coupe
400ci SBC
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