Fuel Injection - Pure-Pontiac EFI Buyer's Guide

Holley Commander 950
Holley offers the Commander 950 ECU as well as the Commander 950 Multi-Point universal fuel-injection kits. The ECU operates in speed density or Alpha-N modes (throttle position sensor and rpm-based computer logic). It (PN 534-120) allows the use of 1-, 2-, or 3-bar MAP sensors and can control eight high-impedance or four low-impedance fuel injectors, or eight low-impedance injectors with an auxiliary injector driver (PN 534-122). Commander 950 Pro software is Windows-based, and the fuel and ignition timing maps can be viewed graphically. The ECU has built-in internal data-logging capability and will interface with multiple timing strategies including GM HEI. This system operates in open- or closed-loop and is capable of controlling a standard O2 sensor or a wide-band O2 sensor when the Wide-band Upgrade kit (PN 534-188) is used.

Universal fuel-injection kits are also available for a 1,000-cfm (PN 534-183; retail $1,496.99, SDPC) or 2,000-cfm (PN 534-184; retail $1,763.99, SDPC) throttle body. The kit contains the Commander 950 ECU, software, wiring harness, fuel rails, MAP, air temperature sensor, oxygen sensor, and billet fuel-pressure regulator. Aluminum fuel rails are included, as are eight injector bungs so you can retrofit the system into the manifold of your choice.

Professional Mass Air Systems
Professional Mass Air Systems markets high-flow mass airflow (MAF) meters, and in addition to supplying Mass-Flo with custom-calibrated GM LS6 MAFs that will fit in the air-cleaner assembly, the company offers its Pro-Tube that places a high-flow MAF within a polished 3- or 3.5-inch aluminum tube. For high-horsepower supercharged and turbocharged applications, the Pro-Tube can be combined with a forced-induction throttle-body (carburetor) bonnet such as ATIs and supports over 1,000 hp.

Professional Mass Air Systems also provides custom MAF tuning to support various GM computer configurations that prevent the MAF from being saturated by the late-model GM computer's nominal 533 grams-a-second measurement capability. Rescaling the MAF on LS1/LS2/LS6 applications allows the stock GM computer to be retained without resorting to an aftermarket ECU.

Rick's Hot Rod Shop
Rick's Hot Rod Shop specializes in musclecar fuel tanks designed to support EFI fuel-system requirements. Custom-made tanks are produced in-house on state of the art CNC machinery and are constructed of 16-gauge 304 stainless steel. The tanks are slightly deeper in the front and have separate front and rear reservoirs as well as integral side-to-side baffling.

Offered in the FI series, the tanks utilize a Walbro GSS 340 in-tank pump rated at 255 lph and retail from $1,195-$1,295 for all popular GTOs and Firebirds. For applications exceeding approximately 600 hp, an enthusiast can purchase a Stealth series tank. For $1,995, this tank features larger -10 inlet and -8 AN return fittings and uses an Aeromotive 11101 in-tank pump to support extreme horsepower.

In addition to new tanks, Rick's will retrofit any new conventional fuel tank with the F1 series Walbro pump for a delivered price including shipping of $495. Non-stocked tanks can be custom made as Rick's has thousands of available tank patterns. Since each EFI tank utilizes a return-style fuel line, Rick's can meet all of your fuel line and regulator needs to allow your EFI conversion to take off.

Speed-Density Versus Mass-Airflow-Metered Systems
In order to explain electronic fuel injection, one must first determine what type of system is being marketed and the advantages and disadvantages of each.

A speed-density-based system uses a throttle position sensor (TPS) located on the throttle body along with a manifold absolute pressure (MAP) sensor to determine load on the engine.

Since the ECU is programmed for a single engine and its inherent volumetric efficiency, when the engine is modified, changes to the tuning have to occur to compensate. Changes are accomplished via a laptop computer with manufacturer-supplied software. Dyno time and/or real-time data collection is necessary in order to adjust the fuel and timing curves to properly tune the engine. Once dialed-in, the speed-density system is very accurate and dependable.

Usually the favorites of power-adder racers and street vehicles alike, speed-density-based systems used to be criticized for poor engine-idle quality. With the advent of faster processors, the idle issue has been addressed and idle characteristics are much improved.

Mass airflow systems use a mass airflow meter to feed data to the ECU. This MAF fuel-injection system uses the intake-air temperature sensor (IAT), a throttle position sensor (TPS), and the amount of air flowing through the MAF as references for the software to determine how much timing and fuel to provide.

The main advantage of a MAF-based system is the ability of the ECU to adjust based on a greater number of data points than a speed-density-based system can provide. Since manifold vacuum is not a contributor to load calculations of a MAF-based system, typically MAF-based systems have better idle and low-speed operating characteristics.

On the downside, packaging a MAF within a classic-Pontiac air-cleaner assembly is difficult, but even that has now been accomplished.

From a power-adder perspective such as turbocharging or supercharging, the ability of the MAF to read the amount of air passing through it has been a limiting factor. A typical GM MAF supports approximately 800 naturally aspirated horsepower.

Sensors

MAP-Manifold Absolute Pressure Sensor: This sensor is plumbed to a manifold vacuum port and measures the difference between the atmospheric air pressure and the pressure (or vacuum) inside the intake manifold. A 1-bar MAP sensor is designed for normally aspirated engines, while forced-induction motors require either a 2-bar (up to 15-psi max boost) or 3-bar (15- to 30-psi max boost) sensor.

MAF-Mass Airflow Sensor: Plumbed into the intake tract, the MAF tells the computer how much air is entering the engine so it can determine the load.

O2 Sensor-Oxygen Sensor: The O2 sensor compares the amount of oxygen in the exhaust stream with the air outside the engine. It outputs a voltage to the ECU, a feedback signal, that the computer uses to modify the amount of fuel delivered to the engine. A narrow-band oxygen sensor outputs any voltage from 0-1 volt: a high voltage if the air/fuel ratio is richer than 14.7:1 and a low voltage if it's leaner. A wide-band O2 sensor (WBO2) can sense a range of air/fuel ratios, from a rich 10:1 to a lean 20:1, with reasonable accuracy. Wide-band O2 sensors are prominent in boosted applications but are useful to all enthusiasts in order to tune the EFI system to its utmost capabilities.

TPS-Throttle Position Sensor: The TPS is usually bolted to the throttle body where it is mechanically synched up with the throttle shaft. As the throttle shaft moves, the TPS signal is provided to the ECU for interpretation. The TPS signal is critical to proper idle function and acceleration enrichment.

ATS-Air Temperature Sensor: The ATS is calibrated to measure the temperature of the air entering the engine. It's usually plumbed as close to the throttle body as possible (i.e., at the base of the air cleaner) to give the most accurate temperature reading.

CTS-Coolant Temperature Sensor: The ECU needs to know the coolant temperature to determine the proper amount of fuel to provide for both cold-start and normal operating temperatures. A CTS not only gives the computer signals to ensure all-around driveability, but when operating temperatures exceed a certain temperature, the ECU can adjust timing and fuel. The coolant temperature sensor is normally tapped into a coolant passage on top of the intake manifold.

Conclusion
Electronic control units and the software to allow the user to quickly tune the engine have made tremendous strides in the past few years. Debate will continue to rage over speed-density versus MAF-based processing units with valid arguments on both sides of the equation. Suffice it to say that due to faster processor speeds, the days of poor engine-idle control due to low-vacuum readings on a MAP sensor are almost behind us.

For the enthusiast looking to convert a classic-Pontiac engine to an EFI system, there are some very good choices in the marketplace. According to Melvin Benzaquen, president of Classic Restorations and a HPP contributor, "research the market and choose a system based on how the engine is modified: drag-race car versus street car."

Planning is the most important factor in completing a successful EFI conversion. Will you use an in-tank pump or a frame-mounted external pump? Hard steel or stainless braided fuel lines? Where is the ECU going to be placed? In the engine compartment? Or does it have to be protected by installing it inside? Routing of the ECU harness, the fuel-pump harness, and the injector harness is also crucial to planning for a neat and orderly installation, as well as making sure everything is routed away from any heat sources and anything that could potentially be chafed or pinched. Hood clearance, especially on a Trans Am, is very critical. Once all these parameters have been explored and worked out, it should make for a smooth installation with minimal problems.