If you're reading this magazine, then we surely don't need to sing the praises of fuel injection. On-road benefits are easier start-up, more consistent performance over elevation changes, and usually better mileage. But hit the dirt, and the difference between a carburetor and injection is like night and day. With injection there's no stumbling, flooding, or missing when your vehicle is operated over rough terrain or at extreme angles. As long as you've got the oil pressure to keep the rotating parts happy, injection will let your rig run upside down or on its side all day long.
We've used lots of aftermarket fuel-injection systems, ranging from fully-exotic MPI setups that require their own intake manifold, electronic ignition, sensors, harness, and computer, to dirt-simple TBI conversions. The exotic systems usually offer the ability to fine-tune for power and drivability, but you need a degree from MIT to understand and manipulate the tuning software. On the other hand, the simple TBI setups require a bit less tuning, but seem to leave a lot of performance and drivability on the table.
We recently acquired a Performance Products Powerjection III fuel-injection system, and believe us when we tell you that this latest iteration is a dream for the average off-road enthusiast. Once the system is bolted to your engine, all you need to do is plug in your laptop and answer a few questions like how many cylinders and the peak torque your engine makes. Then just drive it. That's it. No tuning via laptop or staring at tiny little air/fuel ratio cells until you're blind and half-crazy. The system learns on its own as you drive the vehicle.
Since the engine from our project truck was still on the dyno at Westech Performance, we decided to first see how the Powerjection III stacked up against the carburetor we were using for our testing (see "Jp350, Part II" in this issue). Bolted to an unmoving engine with perfect atmospheric conditions, the Holley 750cfm mechanical secondary double-pumper is a tough act to follow on the dyno, but it would be an absolute nightmare off-road. Heck, it wouldn't even be that pleasant on the street. However, the Powerjection III will deliver nearly the same performance out in the real world as on the dyno. In the dunes, over whoops and dips, or on the street, consistent injected performance will be ours. Check the sidebar in this article Top Twelve Tricks for our favorite aspects of this system. Next month, we'll highlight the installation of the unit in our '68 M-715 and share our on- and off-road driving impressions.
|Engine||Test 1||Test 2|
Test 1: Chevy 350 engine: Lunati Voodoo 227/233 @ 0.050, .489/.504 camshaft, Professional Products Hurricane intake, 1/2-inch phenolic carb spacer, Holley 4779 Double-Pumper carb, 37 degrees ignition timing, 13/4-inch long-tube headers
Test 2: Same as above with carburetor substituted for Powerjection III fuel injection Peak values are in bold
Top Twelve Tricks
The advantages are many, but here are our favorite points about the Powerjection III.
•There's no need to change out your ignition system. A tach signal from the ignition coil or ignition box is all that's required.
•There's no need to swap your intake manifold. The unit uses a standard four-barrel mounting flange, so you can use an affordable one- or two-barrel-to-four-barrel adapter if your intake manifold doesn't already have a square-bore, four-barrel flange.
•The throttle body works with standard carburetor throttle linkage and any off-the-shelf air cleaner with a 55/8-inch carb neck.
•There's no bulky computer to mount, since the computer is located in the throttle body itself.
•The wiring harness consists of only six wires, and technically you only need three of those to make the engine run.
•Comes with the fuel rail, adjustable pressure regulator, and fuel gauge already installed on the throttle body, as well as the correct fuel pump and filter supplied with the PN 70026 or PN 70027 systems. The regulator is pre-set at the required 45psi.
•If the engine stops running, the computer shuts off the fuel pump when the tach signal is lost, which can be beneficial if there's a rollover or crash.
•Four 62lb/hr injectors in the 930cfm throttle body supply enough fuel to feed 550hp, but can also work on small V-8 or V-6 engines. Injectors can be swapped out for smaller units to work with small four-cylinder engines or ordered with four 75lb/hr injectors for up to 600hp.
•It's designed to be installed by the home-hobbyist, so installation and setup are simple and almost everything is included (fuel lines and fittings aren't included, but can be ordered under PN 70107 from Professional Products). There's also no welding required to install the supplied O2 sensor in the exhaust.
•Parts are of high-quality and not Chinese-built junk.
•At roughly $1,500, it's one of the less-expensive systems available.
•There's no tuning necessary! Plug in your laptop , answer a couple of questions such as number of engine cylinders and peak torque, then just drive it. The system self-learns by itself.