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See all 16 photos1. Eric Rosendahl’s 468ci big-block had actually been to run a modified Holley carburetor v some success, yet it was time for an upgrade. The Rat sporting activities iron, oval harbor heads and a Comp hydraulic roller cam making 525 hp and also 560 lb-ft that torque.

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A huge component of power is control. If us can an ext accurately regulate the timing of fuel and also spark come the engine we will accomplish a happier, much more powerful engine. For older muscle cars, this sort of manage used to need a huge investment in electronic fuel injection; a large, different ECU; an anaconda-sized wiring harness; and plenty the esoteric digital skills. Yet not anymore.


Holley’s entry into the self-learning, TBI-style fuel-injection category is the Sniper. The ECU is developed right into the body, i m sorry eliminates lot of the wiring exploit hassles. In fact, connecting the freestanding wires compelled a mere seven connections. That doesn’t acquire much simpler than that. There were other connections because that the water temperature sensor, the oxygen sensor, and also the connector because that the 3.5-inch display, however those were an easy plug-ins. The Sniper TBI unit comes with an combined fuel push regulator. The Sniper uses four 100-lb/hr injectors and also will feed as much as a 650hp normally aspirated engine. The mounting flange provides a double bolt pattern, and with one adapter can even be supplied on a spreadbore-style manifold.


We chose to download the Sniper top top our girlfriend Eric Rosendahl’s 468ci big-block El Camino, figuring the a stout 525hp Rat would placed the Sniper come the test. But before we started the EFI install, we first had come ensure us had an excellent fuel shipment system. Us can’t overemphasize the suggest that great performance from any EFI mechanism starts through a expert fuel distribution system. Us opted for Holley’s RetroFit fuel pump assembly. Our assembly came with a 255-lph pump, billet aluminum mounting flange, and Holley’s distinct Hydramat filter/pickup that will certainly pull fuel native any point of call in the tank. This means if there’s even just a gallon that fuel in the tank, the Hydramat will pick the up.


We mounted that pump assembly in a brand-new fuel tank and likewise retrofitted the car with a complete new UltraPro convoluted PTFE -6 fuel line. In the past, rubber-lined fuel hose has actually had challenge maintaining its integrity over a long duration of time. The rubber hose at some point becomes brittle and begins to leak. Earl’s newly released a new fuel hose product made native polytetrafluoroethylene (PTFE) the is impervious to methanol, ethanol, every those nasty additives choose benzene and toluene in gasoline, and also even to nitromethane. The hose is convoluted (ribbed), i beg your pardon offers an excellent bend radius and makes it very flexible and also easy to route.


The trade-off for this durability is the UltraPro hose is a little more difficult to rally than typical cloth-covered hose, requiring a details ferrule and also hose ends. But once you’ve assembled a couple of the fittings, they go together relatively easily. The beauty, beauty of this hose is that when it is assembled, it need to last the life the the vehicle.


We plumbed a brand-new UltraPro line for the high-pressure distribution side line and re-used the initial 3/8-inch fuel line in the vehicle as the return, instead of a ar 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 also the engine so the it could be accessed quickly for removal and cleaning.


With the Sniper unit installed on the engine and also the fuel lines plumbed, we took this time to wire the remainder that the electrical side. Together the Sniper instructions suggested, we elected to regulate fuel just at this point. We will transform later to full electronic manage over the ignition. So the only wires we had actually to attach were the two huge (12v+ and 12v) dedicated power leads straight to the battery, switched power, and also an rpm sensor to the ECU. Rosendahl had previously to buy a dual-terminal battery that noted a location to connect the power leads straight to the next terminals.


The ECU likewise has a big blue wire that is the strength lead (using an inner relay in the ECU) to journey the fuel pump. We chose to run a specialized ground cable from the electric fuel pump all the method forward come the battery come ensure that the pump had actually full electric power. We likewise chose to develop a two-wire Weatherpak connector at the fuel pump to make servicing simpler with a basic plug-in connector.


With every the electrical connections created, us were ready to start the ECU configuration, however the heads-up display informed united state that our ECU was not correctly configured. This compelled removing the tiny SD map from the heads-up display and also to plug it right into a computer system card reader to download the most present software native Holley’s website.


This demanded quite a little bit of effort on our part as the an initial two map readers us tried failed to do a connection to the Sniper SD card. Us tried a various card and also ultimately a third different SD card reader in a 3rd computer before all the electronic devices were talk to each other. We’ve mounted several other self-learning accelerator body systems and also this was the just one whereby we had to upload brand-new software in bespeak to even to start the process. This yes, really should have actually been accomplished before we derived the system.


After eventually downloading and install the software and also jumping v the suitable electronic hoops, the ideal icons appeared on the handheld maker and we conveniently input the vital information. After all that, we noticed we had actually no fuel pressure. A quick investigation revealed the author had wired the fuel pump backward regardless of checking to make certain the relations were accurate. A basic switch the the ground and also power leads solved that dilemma and also the engine immediately fired increase and resolved into a comfortable idle.


After setting the default idle air/fuel proportion at 13.7:1 and enabling the engine to completely warm up, the only other adjustment was to finalize the idle air control (IAC) number to bring them in line every the instructions. Top top the handheld device, we had actually commanded the idle rpm in ~ 850 however the IAC was reading much greater at 30-35 counts fairly than the 3-8 counts the the indict mentioned. The solution might sound counterintuitive, but in order to mitigate the IAC counts (which is in reality a portion of the IAC opening), we required to open up the curb idle adjustment on the throttle body—much prefer on a regular carburetor.


By opening the throttle knives slightly, this allows much more air right into the engine and also the computer then will command the IAC engine to near slightly, to reduce the IAC count. After ~ a pair of back-and-forth adjustments, we controlled to quickly attain a steady 850-rpm idle speed in Neutral (not in gear) that delivered an IAC counting of 5-6.


We then went because that a fast test drive and also Rosendahl automatically noticed the the throttle solution was much crisper than with the Holley carburetor—even v the exact same ignition timing. The Sniper accelerator bores are the exact same size together the freshly shelved 750 double-pumper carburetor, so the only explanation was the the Sniper provides slightly much better off-idle regulate over the fuel, which enhanced the engine’s response to throttle.


We had additionally fitted Rosendahl’s big-block through a brand-new portable, five-gas exhaust analyzer that us were using as an evaluator for both engine efficiency and just just how close the air/fuel proportion was to what was commanded. The Sniper delivered practically right on target for nearly 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 contempt richer air/fuel ratio at idle.


Initially, we commanded 13.7:1 however discovered the by running slightly richer at 13.2:1, the engine actually idled an ext efficiently with higher CO2 readings. Our theory is that due to the fact that the top on this engine room older steel oval ports, the chambers space not the ideal in regards to efficiency and also need a little much more fuel come command a better idle efficiency.


We likewise noticed the on deceleration the engine seemed to run lot richer 보다 we anticipated. We dubbed Holley and also discovered the the default because that the basic Sniper device does not allow the deceleration fuel cutoff. This is a tiny thing, however should contribute to better fuel mileage—which is a minor issue with this large 468ci Rat. This deserve to be easily permitted by going on Holley’s website and downloading the free Sniper software. This will then enable us come configure the Sniper to permit decel fuel cutoff and also then fill that readjust onto the an international configuration paper using the SD card. The ideal thing to carry out is to read the Sniper instructions and follow the published procedure. The next time us have accessibility to Rosendahl’s car, we arrangement to make this change. This will certainly be many noticeable during in-town driving because that’s where decel fuel cutoff will certainly likely have the most influence on fuel mileage.


Now the Rosendahl has actually put a few hundred miles on the combination, the next step will be come configure the ignition device for digital control. This will allow us to do far an ext finite alters to the ignition in order to dial in the perfect ignition curve because that this engine. This does call for the distributor development to it is in locked out. The Sniper will control either a standard inductive ignition system or a CD, and both are easy to configure.


The Sniper likewise offers dual electric fan controls, a pair of rev regulate features, digital wet nitrous air/fuel ratio control, data logging, too as boost control. These are advanced features that deserve to be personally configured however do require some tuning experience, so make these alters only if you are sure of the changes you are inputting.


Overall, the Sniper installation went smoothly and required only a minimum the tuning to significantly improve the engine throttle an answer and driveability. We took our time converting end to the Sniper and it all went smoothly—especially after we figured out we had actually wired the fuel pump backward.


After steering the car, us do have one critique. It shows up that Holley has used a various throttle affiliation arm top top the Sniper the shortens the street from the throttle pillar to wherein the throttle pedal connects. This quickens the ratio and also increases the effort. This provides the car hard to journey in close web traffic as pedal effort is considerably increased. This makes it basic to open the throttle also far. Holley renders an adapter however we will certainly probably simply make our very own extension.


We still want to convert to complete ignition control, and there room some young cold-start tuning items we’d like to address, but we’ll save those for one more story. In a single highway usage test, the big-block did tear down 14.7 mpg. Not poor for a 525hp Rat. Through a tiny bit the fine-tuning top top the ignition side, it could get a small better. CHP


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See all 16 photos1. Eric Rosendahl’s 468ci big-block had been to run a modified Holley carburetor through some success, yet it to be time because that an upgrade. The Rat sporting activities iron, oval port heads and also a Comp hydraulic roller camer making 525 hp and 560 lb-ft the torque.
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See all 16 photos
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See all 16 photos2. The Holley Sniper accelerator body come in polished, a slick gloss black, or the classic dichromate look shown here. The bolt pattern is global so it will bolt to almost any four-barrel input manifold. The typical Sniper uses four 100-lb/hr injectors and also will feed approximately 650 naturally aspirated horsepower.
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See all 16 photos3. A pair of weeks prior to we began the swap, Rosendahl purchased a new fuel tank indigenous OPG come which we included a Holley in-tank fuel pump kit. Us don’t have actually the an are to detail each step yet the counter took much less than 2 hours. This kit uses a 255-lph pump that deserve to feed 550 normally aspirated EFI horsepower. The kit has the Holley Hydramat pickup/filter that stays clear of loss of fuel pressure because of low fuel conditions.
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See every 16 photos4. To end up the fuel tank conversion, v the module in place we added a pair the 3/8 NPT to -6 male fittings because that the pressure and return connections and likewise fitted the power and also ground relations with a two-pin Weatherpak connector.
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See every 16 photos5. Due to the fact that the Sniper needs a return-style fuel system, we chosen to plumb the El Camino making use of Earl’s new UltraPro convoluted -6 fuel line. This PTFE fuel water tap is impervious even to nitromethane and offers an excellent bend radius for this reason it i will not ~ kink, but it does require its own certain fuel fittings.
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See all 16 photos6. The UltraPro fuel line requires details fittings making use of this sealing ferrule between the fuel line and the fitting. The tapered finish is threaded ~ above the convoluted line, i m sorry seals in between the hose and the fitting.
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See every 16 photos7. The Sniper permits you to regulate both fuel and also spark yet Holley argues you start with simply the fuel making use of your original ignition system, which is what we did. For this reason this requires just connecting the heavy red and also black wires to the battery, the yellow to the an adverse side that the coil, the pink wire to switched 12 volts, and the heavy blue wire directly to the fuel pump. ~ above the upper connector, the only one we offered was the brown command to trigger the tach.
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See all 16 photos8. All self-learning EFI systems prefer the Sniper need a wide-band oxygen sensor. Before our install, Rosendahl had his exhaust shop weld in an oxygen sensor bung right into the exhaust. This bung is preferable yet Holley provides a clamp-on system that walk not need welding.
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See all 16 photos9. The only hiccup in the installation to be after very first powering increase the system, one error post required downloading updated software application from holley.com that had actually to be transferred onto the SD card in the 3.5-inch display. We had actually to try three various SD card readers before we eventually controlled the transfer.
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See all 16 photos10. The 3.5-inch touchscreen shade display is basic to usage and permits you to quickly input the basic information into the screen. As soon as we input the compelled data, the engine started automatically and resolved into a decent idle. Here, the coolant is not approximately temperature but with closeup of the door loop feedback, Sniper is still removing 20 percent fuel from the initial tune at this engine temperature.
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See all 16 photos11. At very first we provided the default idle air/fuel proportion at 13.7:1, climate 13.5:1 (shown) and eventually come 13.2:1. Feedback from ours EMS five-gas exhaust analyzer told united state that this richer setting produced a an ext efficient idle high quality for this particular engine.
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See every 16 photos12. We collection our preferred idle speed at 850 yet noticed the the idle air regulate (IAC) counting was higher than the desired 3-8–percent setting. If this might seem counterintuitive, turning the idle speed screw clockwise rises the lot of air past the throttle, i m sorry decreases the IAC count.
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See all 16 photos13. The Sniper works great, but we’ve still obtained some last touches to perform with assist from the totally free Sniper software we downloaded. Little changes to cold start and after-start enrichment will dial in this system specifically because that this particular engine. This is the volumetric efficiency table. Uneven you have certain tuning experience, it’s best to leave advanced tuning on this tables to a tuner with EFI experience.
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See all 16 photos14. Here’s the Sniper installed and also after it had actually run for an hour or so. The only little of fabrication we had to perform was to develop a brand-new throttle linkage arm the end of 1/4-inch aluminum rod and add a pair of woman spherical joints we uncovered at the hardware store.

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See every 16 photos15. Road experimentation the Sniper consisted of evaluation with the portable EMS five-gas analyzer. We noticed that the Sniper default settings execute not permit closed accelerator fuel cutoff—as evidenced by high HC readings top top deceleration. A Sniper engineer showed us just how to access this and allow the fuel cutoff making use of the free, can be downloaded Sniper EFI software.

Parts List
DescriptionPNSource
Holley Sniper TBI Gold550-516Holley
Holley in-tank fuel pump kitHLY-12-130Summit Racing
Holley billet fuel filter, 10 micronHLY-162-550Summit Racing
Holley billet fuel filter bracketHLY-162-574Summit Racing
Earl’s UltraPro -6 convoluted fuel line, 20"EAR-682006ERLSummit Racing
Earl’s -6 right AN fitting, UltraPro (4)EAR-620106ERLSummit Racing
Earl’s -6 90-degree AN, UltraPro (4)EAR-629106ERLSummit Racing
Earl’s -6 masculine to -6 male adapter (1)EAR-AT981506ERLSummit Racing
Earl’s -6 to 1/4 NPT adapter (2)EAR-AT981606ERLSummit Racing
Earl’s -6 come 3/8 NPT adapter (2)EAR-AT981666ERLSummit Racing
Earl’s -6 tube nut Ano-TuffEAR-AT581806ERLSummit Racing
Earl’s -6 tube sleeve Ano-TuffEAR-AT581906ERLSummit Racing
Earl’s 1/4 NPT to 3/8 male (return)EAR-AT984006ERLSummit Racing