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Fuel & Spark For LS Blocks - How It Works

Getting Fuel and Spark to Your Freshly Swapped LS Small-Block is Easier than Ever. Here’s How.

Stephen Kim Nov 17, 2011
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Manhandling a tail-happy 10-second beast down the dragstrip? Bring it on! Connecting a few innocuous strands of copper where a wiring schematic says they should go? Run for your life! Indeed, hot rodders have a funny way of looking at things sometimes, and electrical intimidation has burst many bubbles of EFI grandeur. Fortunately, that needn’t be the case anymore. In last month’s installment of “How it Works,” we showed how simple it is to fit an LS engine and late-model trans into your classic Bow Tie ride. With all the pre-fabbed motor mounts, crossmembers, and headers at your disposal these days, dropping a Gen III/IV small-block between your car’s framerails is arguably the easiest part of an LS swap. That said, hooking up the electronics, sorting through the wiring, feeding fuel to the lump, and programming the computer isn’t that much harder.

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Thanks to continuing aftermarket innovations, properly wiring up an EFI system is often as simple as connecting four wires. Furthermore, the latest stand-alone computers can literally program themselves. If you’re still not ready to take the EFI plunge, you can even plop a carburetor on an LS small-block and still have it play nice with all the factory sensors. To find out how to feed fuel and spark to a freshly retrofitted LS small-block, we consulted with Rick Anderson of Holley, Jesse Powell of Aeromotive, Damon Sampson of Mast Motorsports, Eric Blakely of Edelbrock, and Mark Campbell of Street and Performance. Equipped with the knowledge provided by our expert panel, the fear of electronics and wiring should never get between you and your aspirations of EFI nirvana.

Stock vs. Aftermarket Computers

Mark Campbell: Using a stock GM computer and wiring harness for an LS swap application can be done, but it takes a bit more effort than using a stand-alone aftermarket system. First off, you need to get a copy of the factory wiring schematics. That way, you can go through it, label every wire, and determine which wires are needed and which ones aren’t. The biggest challenge is programming the computer. You can either send it off to a tuner to set it up for your engine combination, rearend gear ratio, and tire size; you can also purchase tuning software from one of several vendors, and try to tune it yourself. Before you can even fire up the motor for the first time, you have to disable the vehicle antitheft system that’s programmed into the computer. Over the years, GM has used several different computers in LS applications, and not all of them are compatible with various model-year motors. Up until 2005, GM used 24-tooth crankshaft reluctor wheels on Gen III small-blocks, so if you have an earlier LS motor, you’ll need to match it up with an ’05-and-earlier computer. Starting in 2006 in Corvettes and 2007 in trucks, GM switched to 58-tooth crankshaft reluctor wheels in the Gen IV small-block. To run these motors, you need a computer out of a ’06-and-later car or a ’07-and-later truck. While the ’05-and-earlier computers are compatible with both drive-by-cable and drive-by-wire throttle bodies, the newer Gen IV computers will only work in drive-by-wire applications.

Rick Anderson: One of the big advantages of a Holley stand-alone EFI system over a stock GM computer is that you’re working with a system that will grow with your needs regardless of how radical an engine combination might get. The combination of the self-learn feature and the speed-density air metering makes the system much more user friendly once you perform more extensive engine modifications in the future. Getting your motor up and running for the first time is extremely easy even if you don’t have any experience tuning EFI. Holley has many baseline tunes, ranging from stock motors to 1,000hp turbo combinations; you can download off of our website. This helps immensely in getting the motor started, and then the self-learning software will tune the air/fuel mixture from there. Holley offers two stand-alone computers for LS motors, the HP and Dominator systems. The HP system comes with the computer, wiring harness, wideband O2 sensors, and tuning software. It features controls for up to 16 low- or high-impedance fuel injectors, internal data logging, four-stage nitrous control, boost and water injection control, fuel and spark control for individual cylinders, and a one- to five-Bar MAP sensor. Furthermore, it is compatible with both 24- and 58-tooth reluctor wheels. In addition to having all the same capabilities of the HP system, the Dominator system can control up to 24 injectors, interface with a driveshaft speed sensor, and is compatible with drive-by-wire throttle bodies. It can also interface directly with a 4L60E or a 4L80E transmission.

Damon Sampson: With the tuning software that’s out there these days, factory GM computers have been proven to be very capable in performance applications. That said, Mast Motorsports’ stand-alone systems are easier to tune, and offer a wide range of parameters that are easily accessible. We offer two models of computers, the M90 and the M120. The primary difference between them is that the M90 uses dual narrowband O2 sensors, while the M120 has dual wideband sensors. Both computers are designed for a wide variety of applications, ranging from hot rods to airboats to marine applications. As such, our systems feature very durable, OE-like construction with sonic-welded connections and marine-grade wiring. This reduces the potential for wires getting brittle and connections going bad. You can even put our computers under water and they’ll still work. One of the unique features of Mast’s computers is the octane learn function. It continually monitors the knock sensors, and allows you to run on the ragged edge of pump gas. If you were to get a bad batch of gas, the computer will detect this, and dial back timing accordingly. Furthermore, both the M90 and M120 have nitrous and boost controls, and for drive-by-wire motors, you can even tune the sensitivity of the gas pedal.

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Easy Installation

Rick Anderson: Many hot rodders are intimidated by EFI, but Holley has taken measures with our EFI systems to make the installation process as easy as possible. Unlike trying to retrofit a factory GM wiring harness, there is no cutting or splicing involved with our HP and Dominator systems. Our harnesses plug right into the factory LS sensors. All you have to do is connect our harness to the motor, hook up the power and ground, and turn the key. We can’t stress enough the importance of taking your time to wire a vehicle properly. Most problems are attributable to people trying to take shortcuts or not following the directions. For those who need more assistance, we are currently setting up a network of Holley dealers across the country who can help with installation and tuning of Holley EFI systems. To find a dealer near you, check out the map on our website.

Damon Sampson: From an installation standpoint, Mast Motorsports’ ECMs and wiring harnesses were designed to be as flexible and universal as possible. The harness plugs right into the factory sensors, and all you have to do next is wire up the fuel pump wire, a power wire, and a ground wire and the motor will fire right up. It’s literally a simple three-wire hookup. To simplify things even further, the computer and harness are designed to work as independently from your car as possible. The controls for the cooling fans, A/C compressor, and fuel pump are all part of the computer, not your car. So for guys building a car from the ground up, all you have to do is connect the dots.

Self Learning

Rick Anderson: When you go WOT in an engine controlled by a factory GM computer, it switches to open-loop operation. What that means is that the computer ignores the inputs from the O2 sensors, and adjusts the air/fuel ratio based on pre-programmed fuel maps. On the other hand, Holley’s HP and Dominator EFI systems are fast enough that they stay in closed-loop operation even at WOT. This is what makes the self-learning feature possible. The system continually adjusts the air/fuel mixture based on inputs from the O2 sensors. Let’s say you want the engine to run at a 12.7:1 air/fuel mixture; all you do is punch that target air/fuel ratio into the software, and the wideband O2 sensors compensate for it. After 100 miles or more, you can shut off the self-learning function or trim back the adjustability. The system makes adjustments so fast that it’s hard to believe. For example, we put a 100hp dry nitrous system on a motor with a baseline program, and within one pull on the dyno the air/fuel ratio was corrected perfectly.

Before You Buy

Mark Campbell: Not too long ago, people were able to buy a motor, transmission, computer, and wiring together from a salvage yard, but now it’s becoming harder to do so. Even though a salvage yard might bundle them all together as a complete package, these days it’s not uncommon to get a motor and trans from one car, and a computer from another. The model year of the motor and trans, as well as features, such as variable valve timing, flex fuel capability, and displacement on demand can create compatibility issues between the powertrain and the electronics. GM also used 13-, 15-, and 19-pin harness connectors for transmissions. That’s why it’s very important to get the VIN number of the car that the motor came from. As for the wiring harness, keep in mind that the diagnostic link interface and the check engine light should be included with the harness. Sometimes salvage yards will sell you the main harness without the diagnostic link or CEL. Furthermore, harnesses for manual and automatic transmissions are slightly different. The harness for an automatic can be used on a manual trans car. However, using the harness from a manual trans car on an automatic trans requires hard wiring the harness section from an automatic into the main harness. To simplify matters, Street and Performance can make custom harnesses for any application.

Eric Blakely: Many customers already have a carburetor they like, so converting an LS motor to carburetion simplifies the swap process. All that’s required is bolting on an Edelbrock carb-style intake, and plugging the factory GM sensors into the Edelbrock ignition controller to control the spark timing. Not only do we have a dual-plane Performer RPM LS1 intake manifold, we also have a Victor Jr., a Super Victor, and a low-profile dual-quad intake. For motors with LS3-style cylinder heads, we offer a versatile Victor Jr. The Edelbrock ignition controller is a true plug-and-play module, so no programming is required. The timing curve can be changed by plugging in any of the included six timing chips into the receptacle on the timing box. The system uses the stock position sensors to precisely time the firing of each of the eight stock ignition coils. Additionally, we offer two carbureted camshafts for LS motors—a 220/230-at-0.050 grind and a 230/237-at-0.050 grind—to take advantage of the capabilities of the LS engine with our intake manifolds.

Speed Density Advantage

Rick Anderson: Factory GM computers rely on a mass airflow sensor to meter incoming air. That works very well for stock motors, but MAF sensors certainly have their limitations once a big cam or boost is thrown into the mix. A MAF sensor is hot wire that meters air very well, but the problem is that it doesn’t know which direction the air is flowing. As a result, with a big cam it can’t tell the difference between airflow into the intake manifold or reversion. This makes it very difficult to accurately dial in the air/fuel mixture at low rpm. To eliminate this problem, Holley EFI systems utilize speed density air metering. Combined with the system’s self-learning fuel strategy, which communicates with the wideband O2 sensors even at wide-open throttle, all you have to do is punch in a target air/fuel ratio into the software, and the computer takes care of the rest.

Fuel System Mods

Jesse Powell: Setting up a fuel system for EFI is easier than ever, and you should never be scared of tackling such a project. Most factory carbureted fuel systems used either a block-mounted pump or a very small external pump. As such, the easiest way for people to convert a carbureted fuel system over to EFI was by hooking up a 3/8-inch pickup tube to the gas tank, then connecting it to a big external fuel pump. The problem is that without any internal baffling in the tank or a proper sump, the pumps would often suck air and experience premature failure whenever the fuel level dropped below half a tank. As a fuel system manufacturer, Aeromotive realized that we needed to make things easier for our customers. Just handing someone a pump and saying “good luck” wasn’t going to cut it. When you do that, people tend to cut corners and the potential to make mistakes increases. In response, Aeromotive is currently developing a line of stamped, OE-like steel fuel tanks for muscle cars. These tanks will feature internal baffling trays, sending units, and an in-tank fuel pump that flows 340 lph at 43 psi. These pumps will work on both carbureted and EFI motors, and support anywhere between 200 to 1,000 hp. Mounting the pump in the tank will allow it to run cooler, and cut down on noise significantly. Best of all, the entire setup will only cost $500 to $600. Applications include first-gen Camaros, ’64-72 A-bodies, and possibly B-bodies and Tri-Fives. Look for them in early 2012. Aeromotive also offers fuel rails designed specifically for LS motors, in addition to our line of regulators. We even have quick-connect fittings to convert stock LS fuel rails to -AN fittings. CHP


Street And Performance
Mena, AZ
Lenexa, KS 66214
Mast Motorsports
Nagodoches, TX 75964



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