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How to Install Holley Sniper TBI Fuel Injection on a Chevy Big-Block

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Jeff Smith May 7, 2018
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A huge component of performance is control. If we can more accurately control the timing of fuel and spark to the engine we will achieve a happier, more powerful engine. For older muscle cars, this kind of control used to require a huge investment in electronic fuel injection; a large, separate ECU; an anaconda-sized wiring harness; and plenty of esoteric electronic skills. But not anymore.

Holley’s entry into the self-learning, TBI-style fuel-injection category is the Sniper. The ECU is built right into the body, which eliminates much of the wiring harness hassles. In fact, connecting the freestanding wires required a mere seven connections. It doesn’t get much simpler than that. There were other connections for the water temperature sensor, the oxygen sensor, and the connector for the 3.5-inch display, but those were simple plug-ins. The Sniper TBI unit comes with an integrated fuel pressure regulator. The Sniper uses four 100-lb/hr injectors and will feed up to a 650hp naturally aspirated engine. The mounting flange offers a dual bolt pattern, and with an adapter can even be used on a spreadbore-style manifold.

We decided to install the Sniper on our friend Eric Rosendahl’s 468ci big-block El Camino, figuring that a stout 525hp Rat would put the Sniper to the test. But before we started the EFI install, we first had to ensure we had an excellent fuel delivery system. We can’t overemphasize the point that good performance from any EFI system starts with a professional fuel delivery system. We opted for Holley’s RetroFit fuel pump assembly. Our assembly came with a 255-lph pump, billet aluminum mounting flange, and Holley’s unique Hydramat filter/pickup that will pull fuel from any point of contact in the tank. This means if there’s even just a gallon of fuel in the tank, the Hydramat will pick it up.

We installed that pump assembly in a new fuel tank and also retrofitted the car with a complete new UltraPro convoluted PTFE -6 fuel line. In the past, rubber-lined fuel hose has had difficulty maintaining its integrity over a long period of time. The rubber hose eventually becomes brittle and begins to leak. Earl’s recently released a new fuel hose material made from polytetrafluoroethylene (PTFE) that is impervious to methanol, ethanol, all those nasty additives like benzene and toluene in gasoline, and even to nitromethane. The hose is convoluted (ribbed), which offers an excellent bend radius and makes it very flexible and easy to route.

The trade-off for this durability is the UltraPro hose is a little more difficult to assemble than normal cloth-covered hose, requiring a specific ferrule and hose ends. But once you’ve assembled a couple of the fittings, they go together fairly easily. The beauty of this hose is that once it is assembled, it should last the life of the vehicle.

We plumbed a brand-new UltraPro line for the high-pressure delivery side line and re-used the original 3/8-inch fuel line in the car as the return, replacing a section of the line that had been damaged after 50 years in the car. We also included a Holley 10-micron fuel filter located roughly halfway between the tank and the engine so that it could be accessed easily for removal and cleaning.

With the Sniper unit installed on the engine and the fuel lines plumbed, we took this time to wire the remainder of the electrical side. As the Sniper instructions suggested, we elected to control fuel only at this point. We will convert later to full electronic control over the ignition. So the only wires we had to connect were the two large (12v+ and 12v) dedicated power leads directly to the battery, switched power, and an rpm sensor to the ECU. Rosendahl had previously purchased a dual-terminal battery that provided a place to connect the power leads directly to the side terminals.

The ECU also has a large blue wire that is the power lead (using an internal relay in the ECU) to drive the fuel pump. We decided to run a dedicated ground wire from the electric fuel pump all the way forward to the battery to ensure that the pump had full electrical power. We also chose to build a two-wire Weatherpak connector at the fuel pump to make servicing easier with a simple plug-in connector.

With all the electrical connections created, we were ready to start the ECU configuration, but the heads-up display informed us that our ECU was not properly configured. This required removing the small SD card from the heads-up display and to plug it into a computer card reader to download the most current software from Holley’s website.

This demanded quite a bit of effort on our part as the first two card readers we tried failed to make a connection to the Sniper SD card. We tried a different card and ultimately a third different SD card reader in a third computer before all the electronic devices were talking to each other. We’ve installed several other self-learning throttle body systems and this was the only one where we had to upload new software in order to even to begin the process. This really should have been accomplished before we obtained the system.

After eventually downloading the software and jumping through the appropriate electronic hoops, the appropriate icons appeared on the handheld device and we quickly input the necessary information. After all that, we noticed we had no fuel pressure. A short investigation revealed the author had wired the fuel pump backward despite checking to make sure the connections were accurate. A simple switch of the ground and power leads solved that dilemma and the engine immediately fired up and settled into a comfortable idle.

After setting the default idle air/fuel ratio at 13.7:1 and allowing the engine to fully warm up, the only other adjustment was to finalize the idle air control (IAC) numbers to bring them in line per the instructions. On the handheld device, we had commanded the idle rpm at 850 yet the IAC was reading much higher at 30-35 counts rather than the 3-8 counts that the instructions mentioned. The solution might sound counterintuitive, but in order to reduce the IAC counts (which is actually a percentage of the IAC opening), we needed to open the curb idle adjustment on the throttle body—much like on a normal carburetor.

By opening the throttle blades slightly, this allows more air into the engine and the computer then will command the IAC motor to close slightly, reducing the IAC count. After a couple of back-and-forth adjustments, we managed to quickly achieve a stable 850-rpm idle speed in Neutral (not in gear) that delivered an IAC count of 5-6.

We then went for a quick test drive and Rosendahl immediately noticed that the throttle response was much crisper than with the Holley carburetor—even with the same ignition timing. The Sniper throttle bores are the same size as the recently shelved 750 double-pumper carburetor, so the only explanation was that the Sniper offers slightly better off-idle control over the fuel, which improved the engine’s response to throttle.

We had also fitted Rosendahl’s big-block with a new portable, five-gas exhaust analyzer that we were using as an evaluator for both engine efficiency and just how close the air/fuel ratio was to what was commanded. The Sniper delivered nearly right on target for almost all the part throttle and idle commanded air/fuel ratios. Using this analyzer, we discovered that the engine seemed to idle more efficiently with a slightly richer air/fuel ratio at idle.

Initially, we commanded 13.7:1 but discovered that by running slightly richer at 13.2:1, the engine actually idled more efficiently with higher CO2 readings. Our theory is that since the heads on this engine are older iron oval ports, the chambers are not the best in terms of efficiency and need a little more fuel to command a better idle efficiency.

We also noticed that on deceleration the engine seemed to run much richer than we anticipated. We called Holley and discovered that the default for the base Sniper system does not enable the deceleration fuel cutoff. This is a small thing, but should contribute to better fuel mileage—which is a minor concern with this big 468ci Rat. This can be easily enabled by going on Holley’s website and downloading the free Sniper software. This will then allow us to configure the Sniper to enable decel fuel cutoff and then load that change onto the global configuration file using the SD card. The best thing to do is to read the Sniper instructions and follow the published procedure. The next time we have access to Rosendahl’s car, we plan to make this change. This will be most noticeable during in-town driving since that’s where decel fuel cutoff will likely have the most impact on fuel mileage.

Now that Rosendahl has put a few hundred miles on the combination, the next step will be to configure the ignition system for digital control. This will allow us to make far more finite changes to the ignition in order to dial in the perfect ignition curve for this engine. This does require the distributor advance to be locked out. The Sniper will control either a standard inductive ignition system or a CD, and both are easy to configure.

The Sniper also offers dual electric fan controls, a couple of rev control features, digital wet nitrous air/fuel ratio control, data logging, as well as boost control. These are advanced features that can be individually configured but do require some tuning experience, so make these changes only if you are sure of the modifications you are inputting.

Overall, the Sniper installation went smoothly and required only a minimum of tuning to drastically improve the engine’s throttle response and driveability. We took our time converting over to the Sniper and it all went smoothly—especially after we figured out we had wired the fuel pump backward.

After driving the car, we do have one critique. It appears that Holley has used a different throttle linkage arm on the Sniper that shortens the distance from the throttle shaft to where the throttle pedal connects. This quickens the ratio and increases the effort. This makes the car hard to drive in close traffic as pedal effort is dramatically increased. This makes it easy to open the throttle too far. Holley makes an adapter but we will probably just make our own extension.

We still want to convert to full ignition control, and there are some minor cold-start tuning items we’d like to address, but we’ll save those for another story. In a single highway mileage test, the big-block did knock down 14.7 mpg. Not bad for a 525hp Rat. With a little bit of fine-tuning on the ignition side, it might get a little better. CHP


1. Eric Rosendahl’s 468ci big-block had been running a modified Holley carburetor with some success, but it was time for an upgrade. The Rat sports iron, oval port heads and a Comp hydraulic roller cam making 525 hp and 560 lb-ft of torque.


2. The Holley Sniper throttle body comes in polished, a slick gloss black, or the traditional dichromate look shown here. The bolt pattern is universal so it will bolt to nearly any four-barrel intake manifold. The standard Sniper uses four 100-lb/hr injectors and will feed up to 650 naturally aspirated horsepower.


3. A couple of weeks before we began the swap, Rosendahl purchased a new fuel tank from OPG to which we added a Holley in-tank fuel pump kit. We don’t have the space to detail each step but the conversion took less than 2 hours. This kit uses a 255-lph pump that can feed 550 naturally aspirated EFI horsepower. The kit includes the Holley Hydramat pickup/filter that prevents loss of fuel pressure due to low fuel conditions.


4. To finish the fuel tank conversion, with the module in place we added a pair of 3/8 NPT to -6 male fittings for the pressure and return connections and also fitted the power and ground connections with a two-pin Weatherpak connector.


5. Since the Sniper requires a return-style fuel system, we elected to plumb the El Camino using Earl’s new UltraPro convoluted -6 fuel line. This PTFE fuel hose is impervious even to nitromethane and offers an outstanding bend radius so it won’t kink, but it does require its own specific fuel fittings.


6. The UltraPro fuel line requires specific fittings using this sealing ferrule between the fuel line and the fitting. The tapered end is threaded onto the convoluted line, which seals between the hose and the fitting.


7. The Sniper allows you to control both fuel and spark but Holley suggests you start with just the fuel using your original ignition system, which is what we did. So this requires only connecting the heavy red and black wires to the battery, the yellow to the negative side of the coil, the pink wire to switched 12 volts, and the heavy blue wire directly to the fuel pump. On the upper connector, the only one we used was the brown lead to trigger the tach.


8. All self-learning EFI systems like the Sniper require a wide-band oxygen sensor. Prior to our install, Rosendahl had his exhaust shop weld in an oxygen sensor bung into the exhaust. This bung is preferable but Holley supplies a clamp-on system that does not require welding.


9. The only hiccup in the installation was after first powering up the system, an error message required downloading updated software from holley.com that had to be transferred onto the SD card in the 3.5-inch display. We had to try three different SD card readers before we eventually managed the transfer.


10. The 3.5-inch touchscreen color display is easy to use and allows you to quickly input the basic information into the screen. Once we input the required data, the engine started immediately and settled into a decent idle. Here, the coolant is not up to temperature but with closed loop feedback, Sniper is still removing 20 percent fuel from the initial tune at this engine temperature.


11. At first we used the default idle air/fuel ratio at 13.7:1, then 13.5:1 (shown) and eventually to 13.2:1. Feedback from our EMS five-gas exhaust analyzer told us that this richer setting produced a more efficient idle quality for this particular engine.


12. We set our desired idle speed at 850 but noticed that the idle air control (IAC) count was higher than the desired 3-8–percent setting. While this may seem counterintuitive, turning the idle speed screw clockwise increases the amount of air past the throttle, which decreases the IAC count.


13. The Sniper works great, but we’ve still got some final touches to perform with help from the free Sniper software we downloaded. Small changes to cold start and after-start enrichment will dial in this system specifically for this particular engine. This is the volumetric efficiency table. Unless you have specific tuning experience, it’s best to leave advanced tuning on these tables to a tuner with EFI experience.


14. Here’s the Sniper installed and after it had run for an hour or so. The only bit of fabrication we had to do was to build a new throttle linkage arm out of 1/4-inch aluminum rod and add a pair of female spherical joints we found at the hardware store.


15. Road testing the Sniper included evaluation with the portable EMS five-gas analyzer. We noticed that the Sniper default settings do not enable closed throttle fuel cutoff—as evidenced by high HC readings on deceleration. A Sniper engineer showed us how to access this and enable the fuel cutoff using the free, downloadable Sniper EFI software.

Parts List
Description PN Source
Holley Sniper TBI Gold 550-516 Holley
Holley in-tank fuel pump kit HLY-12-130 Summit Racing
Holley billet fuel filter, 10 micron HLY-162-550 Summit Racing
Holley billet fuel filter bracket HLY-162-574 Summit Racing
Earl’s UltraPro -6 convoluted fuel line, 20' EAR-682006ERL Summit Racing
Earl’s -6 straight AN fitting, UltraPro (4) EAR-620106ERL Summit Racing
Earl’s -6 90-degree AN, UltraPro (4) EAR-629106ERL Summit Racing
Earl’s -6 male to -6 male adapter (1) EAR-AT981506ERL Summit Racing
Earl’s -6 to 1/4 NPT adapter (2) EAR-AT981606ERL Summit Racing
Earl’s -6 to 3/8 NPT adapter (2) EAR-AT981666ERL Summit Racing
Earl’s -6 tube nut Ano-Tuff EAR-AT581806ERL Summit Racing
Earl’s -6 tube sleeve Ano-Tuff EAR-AT581906ERL Summit Racing
Earl’s 1/4 NPT to 3/8 male (return) EAR-AT984006ERL Summit Racing

Photos by Jeff Smith


Summit Racing
Akron, OH
Original Parts Group Inc. (OPGI)
Seal Beach, CA 90740
Holley Performance Products
Bowling Green, KY 42101



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