In the March '10 issue, I dyno'd a warmed-over Chevy 350 I built for my '68 M-715 and topped it off with a Professional Products Powerjection III fuel-injection system. Despite a rumpity cam with a narrow (for fuel-injection) 110-degree lobe separation angle and a huge Professional Products Hurricane single-plenum intake manifold, the engine idled nicely down to 750rpm and delivered 388hp @ 6,200rpm and a flat torque curve that peaked at 399lb-ft @4,200rpm. It's all good stuff in a controlled dyno environment, but how would it work in the real world, where operating temperatures, atmospheric conditions, and pump gas quality come into play? Those are the questions a surprising number of you emailed after the first installment of this story.
Well, the Powerjection III is now on the truck and I've been driving the rubber off the rear tires-literally. It's got power on tap to fry the hides pretty much whenever I want. And as for the Powerjection III's ease of install and drivability with no tuning? It's completely true.
The injection comes with very detailed installation instructions, and it's an intuitive system that goes on easy in an afternoon. The hardest part is building the high-pressure fuel lines if your vehicle isn't already equipped. And since the injection remembered my engine from the dyno, I didn't even need to plug in my laptop. I just fired it up and let it settle into an idle for a minute or two before my first drive. It took a couple of miles for the system to fully come up to speed, but after that the drivability and power delivery were way better than I had ever experienced with this truck. You just mash your foot down and there's no complaining; the engine just hunkers down and pulls strong up to my self-imposed redline of 6,500rpm. Buzzing down the road there's no more smell of unburned exhaust from an overly-rich carb, and I swear that the fuel gauge isn't dropping as quickly.
On the road, the power delivery is smooth and linear down below 3,000rpm and when rowing through the gears. It's so nice to have that off-idle stumble of the old carburetor gone. Once in a while I do note some very slight hesitation, but I attribute that to the huge intake manifold plenum and not the injection. In fact, having owned similarly-built engines running carburetors, I'm amazed that this combination is as drivable as it is at lower rpms. Off-road, even with sustained slow-speed crawling, the injection keeps the engine from loading and stumbling despite the race-oriented intake. It maintains a docile manner until I get impatient and put my foot in it, at which time it springs to life like an ax murderer lunging at a victim. And naturally, it'll do so at any angle no matter how steep, bumpy, or undulating the terrain.
To answer in a nutshell all the reader questions asking what the catch was with this easy-to-install, surprisingly affordable fuel-injection system, I'm happy to report that there doesn't seem to be one. So far, it's proven to be a great injection system that's worth the entry fee.
With the injection wiring...
With the injection wiring squared away, I drilled a 7/8-inch hole for the oxygen sensor downstream where the two cylinder banks meet. You don't want to install the sensor too far downstream or there won't be enough heat to get a proper reading. Generally, as long as you're forward of the bellhousing, you're okay. Although you can weld in the supplied O2 bung, Professional Products designed this system to be installed by most home hobbyists, so I went the low-tech way and used the gasket and hose clamps as shown. The bung is designed for smaller primary-size tubing and my 3-inch-diameter pipe is a bit too big to fully seal. I'll be welding the bung on in the future to eradicate the very slight puff of exhaust that escapes past the gasket.
The 12-volt fuel pump and...
The 12-volt fuel pump and fuel filter come with the PN 70026 injection system, but the optional fuel line kit (PN 70107) can be purchased separately and includes nearly everything you need to build your high-pressure fuel system, including -6AN fittings, -6AN hose, and bulkhead fittings. Whether not part of the kit or an omission on their part, my kit didn't include the bulkhead nuts or nylon gaskets. I wanted to run a pre-filter despite the instructions directing me to rely on the stock in-tank fuel sock, so I picked up a pre-filter from my local VW shop when I was there buying the bulkhead fitting parts.
After installing the engine...
After installing the engine back in the M-715, I was surprised to find that I had to replace the factory-type starter because the added compression and increased cranking pressure of the newly-rodded engine was overwhelming the stock-type starter. I ordered a Summit Racing Protorque high-torque mini starter (PN SUM-820323-OS) to spin the engine easily during startup.
After sending my stock M-715...
After sending my stock M-715 tank out to be cleaned and sealed, I cut a hole in the top to allow access to the bulkhead fitting nuts from behind and installed two -6AN fittings for the pickup and return lines. I fashioned a simple aluminum plate and sealed it with a homemade gasket and sheetmetal screws. I could've hooked the return line into the stock fuel pickup line, but I figured a dedicated AN fitting way was cleaner.
While I was at it, I also...
While I was at it, I also ordered a new Summit Racing HEI cap and rotor (PN SUM-850010) and new 8.5mm plug wires (PN SUM-888836) to ensure a good performance baseline for the injection evaluations. Then it was a matter of unbolting the old carburetor, tossing it over my shoulder, and bolting the Powerjection III in its place. The carb linkage hooked right up and I then connected the six wires as per the instructions: battery, key-on 12-volt, tach signal, O2 sensor, water temp sensor, and fuel pump.
I welded some plates to the...
I welded some plates to the framerails to which I mounted the fuel pump and filter, then built the fuel lines using the hose and fitting supplied in the part number 70107 kit. I was doubtful at first, but the kit actually included more fuel line than I needed for the long 126-inch wheelbase truck. So far the hose is free of leaks, but since modern unleaded fuel additives can wreak havoc on most AN hoses over time, I'll continue to check it periodically.