Installing Holley Sniper Quadrajet fuel injection on a 1972 Chevy Nova

01 Holley sniper quadrajet efi istall David Whitmer’s Nova — David Whitmer’s Nova does dual duty as a driver and now family hauler. Adding modern, Holley Sniper EFI was a natural next step to make it more reliable.

Installing Holley Sniper Quadrajet Fuel injection on a 1972 Nova

By Evan Perkins – Photography by the Author

Cars were meant to be driven. David Whitmer’s 1972 Nova with the ultrarare Sky Roof option is no exception. Whitmer restored the car after high school by rebuilding all the mechanical bits, replacing multiple rotten panels, and lovingly blocking the body on which he sprayed the paint.

The Nova has garnered plenty of street miles since its restoration, now with Whitmer’s wife and young daughter in tow. With even more family outings planned, more road miles to be earned, and considerably more precious cargo, it was time to up the reliability, driveability, and fun factor of the car once again. That process entailed a switch to modern, electronic fuel injection.

The Nova’s engine is the factory-equipped 350ci small-block, which was treated to a bore, hone, oversized cast pistons, and a pair of camel hump cylinder heads. It’s still happily chugging along all these years later, but the Quadrajet carburetor living atop left some performance to be desired. The solution was a switch to Holley’s Sniper Quadrajet EFI system (PN 550-869). The system resembles a factory carburetor and even perches neatly on a Quadrajet intake, requiring no modification or adapter plates. The upside is an OEM-esque look with modern electronic fuel injection performance and laptop tunability.

02 Holley sniper quadrajet efi istall Quadrajet variant — The Sniper EFI chosen for this build was a Quadrajet variant.

Installing Sniper EFI

Adding throttle body fuel injection via the Sniper system was the least-intrusive way to introduce EFI to the already-running engine. Had Whitmer decided to go the port fuel injection route, the Edelbrock intake manifold would have had to be removed, machined, and welded for injector bungs and rails or replaced entirely. Wanting to retain as much of his original setup as possible, this was an ideal fit.

03 Holley sniper quadrajet efi istall integrated ECU, fuel injectors, and relevant EFI sensors — The unit resembles a carburetor but contains an integrated ECU, fuel injectors, and relevant EFI sensors.

The Sniper uses a spread-bore throttle-blade arrangement just like the outgoing Quadrajet carburetor and bolts directly to the intake flange of the manifold. It accepts the standard Quadrajet throttle linkage and kickdown cable for the TH350 transmission, which simplifies installation significantly.

04 Holley sniper quadrajet efi istall engine bay — In the engine bay, it’s hard to identify the Sniper system apart from a carburetor, especially once the air cleaner is installed.

Wiring the Sniper was relatively straightforward as well, with the Sniper needing a 12V ignition source, positive and negative battery connections, an O2 sensor bung installed, and the coolant temperature sensor to be plumbed into the thermostat housing area of the intake manifold. The rpm input came by way of the Holley HyperSpark distributor and ignition box, which plug directly into the Sniper harness.

05 Holley sniper quadrajet efi istall — One of the major fuel system differences between a carburetor and EFI is the need for a high-pressure pump. This retrofit fuel module installs in the factory tank by use of a large holesaw. The pump top hat has a port for the outlet, return, and vent. The original vent on the tank was retained so the new port was plugged.

Fuel System

When moving from a carburetor to EFI, one of the most important supporting changes is a new fuel system. Carburetors are more than happy to chug along on mechanical fuel pumps that deliver 5-9 psi of fuel pressure. Fuel injection systems are not and require around 60 psi (for Sniper) to run.

06 Holley sniper quadrajet efi istall Holley does offer EFI-ready tanks that are internally baffled and include a built-in EFI pump — Whitmer opted to replace the Nova’s original tank with a stock replacement unit, rather than clean the rust and grime out of the original. Holley does offer EFI-ready tanks that are internally baffled and include a built-in EFI pump.

To suit Whitmer’s Nova, a Holley die-cast fuel module was sourced. This was installed in a factory-replacement style tank, though Holley does offer retrofit EFI tanks that have the pump already inside. A 3-inch holesaw was used to cut through the tank’s corrugated surface and the pump dropped in place. Swing-out cams and a thick, neoprene gasket did the job of sealing up the new pump. On top of the module are ports for pressure, return, and a vent, making plumbing the new lines very simple.

07 Holley sniper quadrajet efi istall Holley fuel pressure regulator — While many Sniper systems contain an integrated fuel pressure regulator, the Quadrajet version does not, necessitating an external regular like this Holley unit shown.

Ignition Control

While many gearheads will opt to have the Sniper control only the fueling demands of the engine, it can also control ignition. Whitmer used a HyperSpark distributor, HyperSpark ignition coil, and HyperSpark ignition box so that everything could be integrated simply into the Sniper and controlled via its software.

08 Holley sniper quadrajet efi istall HyperSpark distributor — Sniper EFI can control both EFI and spark, so Whitmer opted for a HyperSpark distributor. The distributor is plug-and-play into the Sniper and allows timing to be set via the Sniper tune.

The system is a plug-and-play into the Sniper EFI harness, and the ability to create a load-based timing map will allow the car to gain additional fuel economy at cruise, start better cold, and even help to stabilize idle speed through quick adjustments by the computer. The ignition timing can also be changed digitally. Once the initial timing is synced and verified, there’s no longer a need to break out the timing light for future changes to ignition advance. A fresh set of MSD wires with HEI-style ends and eight new spark plugs rounded out the ignition upgrades.

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09 Holley sniper quadrajet efi istall HyperSpark ignition box and coil — A HyperSpark ignition box and coil were also utilized. To prevent any issues with electronic noise, they were mounted in the fenderwell behind the inner fender.

On the Dyno

David utilized the included 3.5-inch handheld to initialize the Sniper system and, after a bit of cruising around the neighborhood, drove it to Westech Performance for chassis dyno tuning.