How to Convert from Carb to EFI on an LS-Swapped Camaro with Sniper

10 min read

How to Convert from Carb to EFI on an LS-Swapped Camaro with Sniper

10 min read

There are those of us that eagerly embrace new technology. You’ll stand in line for hours in order to get your hands on the latest phone, watch, camera or any other device that promises to make your life easier – or at least help to make you look cooler. Going along with that, of course, is your willingness to spend even more hours fiddling with the thing to learn how it works and what it can do for you. Whether you actually save any time or realize any real benefit is irrelevant…getting to use the device is its own reward.

You’re also the type that loves how technology has crept further and further into and now totally controls practically every aspect of new cars today. Ok, near four-figure factory horsepower levels is just simply over the top awesome. We have got to give you that one.

But there are still some of us that like to keep things simple. You want to make your own decisions, not have some computer making them for you. When you floor the pedal, you expect the throttle plates to open, all the way, and not have some program tell you that, “no, you shouldn’t do that right now, let me ease you into it.”

Short version; you love what the tech can do but you want to be in control and you don’t want to have to go back to school to learn how to use it. In other words, you want the benefits but it can’t be too complex or finicky.

Holley Sniper EFI Kit

This is the Sniper EFI Stealth kit. Don’t let the wiring scare you. It’s actually very easy to plug it all together. Notice that there is not a separate ECU box. The “computer” is contained within the Sniper unit itself.

Muscle Car Restorations (MCR) has embraced advanced engine management systems as they became available and have built some remarkable projects with them but a trained technician has always been necessary to deliver an amazing customer end experience.

But what many of us have wanted was something for old school muscle cars that could be more or less bolted in place so classic car owners could realize the benefits of EFI with a vintage engine without needing to be a full-on computer geek to get it to work – ideally without needing a laptop at all.

Well, Holley has done just that with their Sniper EFI. MCR install this Sniper EFI Stealth 4150, complete with their EFI Conversion Fuel Tank Kit, and it's about as plug-and-play as possible.

The subject vehicle was a ’69 Camaro with a mild 355ci LS and a manual transmission. MCR installed the fuel tank kit with sending unit and electric in-tank fuel pump. Holley recommends this set up as the baffled tank prevents fuel starvation and the pump will run much cooler and quieter. There is a reason all factory fuel pumps are in-tank. If you do need to go with an inline pump, be certain it can provide at least 60 PSI of fuel pressure to the Sniper unit.

Holley Sniper Stealth EFI throttle body

Looking very much like a classic Holley carb, the Sniper Stealth will bolt onto any 4150 style manifold. Note that there is a 4500 version as well.

Bolting on the Sniper Stealth is just like bolting on a carburetor, including the throttle and (if necessary) transmission linkage. The Sniper also has vacuum ports for vacuum advance units and power brake boosters. If you are running a carburetor, you can run a Sniper.

MCR installed a fuel pressure regulator with a liquid filled gauge on the firewall. Adequate fuel pressure is an absolute must and this gauge allows constant monitoring during set up and initial fire up. Of course, an oxygen sensor and coolant temperature sensor will need to be installed, but everything else is contained within the Sniper unit itself. If the wiring looks a little intimidating at first let me tell you that it’s not really a big deal. Just follow the instructions and you’ll be fine. Depending on your setup, some of the wiring will not be used. The harness has lots of optional inputs and outputs that can be taken advantage of only if the end user desires.

Once powered up, the Touch Screen LCD guides you through the setup process. Just input the correct values and you’ll be ready to go. While there are a number of parameters that can be fine tuned on a laptop if necessary, MCR left the factory presets in place and one turn of the key had the engine running and quickly settling into a comfortable idle.

Once warmed up, the idle air control (IAC) percentage was set, and the car was driven across the property to MCR’s Mustang Dyno building. Following Holley’s instructions, the Camaro was driven on the dyno, lightly at first, through various loads and speeds simulating normal neighborhood driving. No adjustments were necessary. Things like coolant enrichment (choke function) and accelerator enrichment (accelerator pump) worked fine right out of the box. MCR prefers to do this initial evaluation on the dyno where they can keep a close eye on everything but truthfully, aside from that, this thing could have been taken out for an easy cruise right away.

Everything checked out fine so more and more power and RPM was added until it was felt that the Sniper had learned enough to go for some full power dyno runs. And apparently it had, as the first full power pull yielded 374 horsepower (to the rear wheels) at 5900 RPM and 352 lb-ft of torque. Subsequent pulls were virtually the same – no stumbles, no hiccups, no hesitations, just clean full-power runs. And keep in mind that, except for a custom timing curve added to the MSD box, the Sniper itself was completely set up without the use of a laptop. The system does include a data logger should diagnostics be necessary or if you want to totally geek out on all the various stats that can be recorded.

Frankly, the most difficult part of this install was the fuel tank and lines. If you think you can manage that, then you can certainly handle a Sniper Stealth installation. Fair warning guys, you do need to read the instructions! They are detailed but not complicated, though there are some specifics to read like the information regarding the wiring, which must be followed precisely.

If you are old school at heart and have been a bit wary of state of the art tech, then a Sniper could be just what you’ve been hoping for – all the benefits of EFI with none of the excuses.

Sniper EFI Stealth fuel pressure regulator

An external fuel pressure regulator is mandatory with the Sniper Stealth system to provide, maintain and confirm that there is a constant 48 PSI to the injectors. Other Sniper variants have built-in fuel pressure regulators.

Sniper EFI Stealth MSD LS Series

While the Sniper has the ability to control timing with Holley Dual Sync, Hyperspark, or various OEM distributors, LS engines will require an ignition controller. MCR went with an MSD LS Series.

Sniper EFI Touchscreen Home Screen

Once everything is wired and the power is on, the Touch Screen LCD will light up and you’ll be able to run through the easy set up process. Just touch the Wizard icon and make your selections.

Sniper EFI Stealth ignition timing curve

One of the real benefits to utilizing the MSD LS Series ignition controller is to be able to design your own timing curve with MSD software. This particular LS was producing an audible knock on fire up so the timing was pulled back for the initial start-up, solving the issue.

Sniper EFI Stealth Throttle Plate Screw

About the only mechanical adjustment required is setting the throttle plate screw so the IAC Position reads between 2% and 10%. The TPS position should stay at 0% but if it does read higher cycling the ignition switch should set it back to 0% again.

Sniper EFI Stealth 1969 Camaro dyno runs

The Sniper learns by simply varying engine speed and load and by normal driving time. MCR does this on their Mustang dyno. You might expect that it would take a few full power-on runs to learn how to make max power, but that was not the case. The Sniper got it right on the first WOT run, producing 374 HP at 5900 RPM. Additional runs showed virtually no difference. The learning was fast and accurate. No hassle. No fussing around. It just worked.


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