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