We saw this mechanical fuel-injection setup on a street-driven big-block Chevy at Cruisin' Grand, the Escondido, California, cruise, so there is hope for the brave souls who do want to run mechanical fuel injection. Anything is possible with enough tuning time.
Mechanical Fuelie Mopar
Doug Rempel, Hebron, NE: I bought a complete Hilborn setup minus hoses and fittings that fit my Dodge 440. Everything I have read says it is not very street friendly. I am willing to tune it for driveability versus track time. I plan on getting the system flowed and set up for a baseline. Will the driveability really be that bad? What about performance versus a carb at the track?
Jeff Smith: We've had only limited personal experience with mechanical fuel-injection systems on a blower, Doug, and we've also heard the same kinds of things about these injection systems. We're going to assume you want to make this system work for a street-driven car rather than a drag-race-only combination. Basically, mechanical fuel-injection systems are designed to perform best in two areas: idle and wide-open throttle (WOT). The aspect you will find most challenging and what should be of most concern for a street-driven engine is part-throttle.
Converting a Hilborn mechanical fuel-injection manifold over to EFI is not really that difficult. You can even install the injector bungs without welding using epoxy. This is a small-block Ford manifold that our buddy Tim Moore is converting for his 289-powered GT-40 replicar.
There are a couple of issues involved with tuning an individual runner manifold like a Hilborn. First, all the throttle plates must be set to flow the same amount of air. You can get close with a feeler gauge on the opening, but to truly set them properly, you need to measure the amount of air going through each stack. There used to be a little device called a uni-synch that can be found occasionally on eBay that measures the amount of airflow at idle for each stack, and all you do is set all the stacks the same.
Next, you need to establish fuel pressure. Most mechanical systems use a mechanical pump and tie in pump speed with fuel delivery. You can probably get help from Hilborn establishing your nozzle sizes for the injectors based on engine size and the amount of power you realistically are making. Nozzle diameters will also be affected by the amount of fuel pressure and the size and number of high-speed bleed orifices. The more pressure you run, the smaller the nozzles and the better the atomization, but this added pressure also reduces pump life.
After all that, the real tuning begins with the barrel valve. This valve sets the amount of fuel that is returned to the tank with the remainder delivered at idle to the nozzles. This valve is adjustable, but you can't go too lean or the engine will probably stumble in transition to part- or full-throttle. Generally, the package will have to be set very rich to accommodate the dizzying number of variable-load characteristics present at part-throttle. The shape of the barrel valve will determine the amount of fuel delivered to the engine at part-throttle. It is possible to dial in the shape of that barrel valve to fit the requirements of your engine, but be prepared to spend lots of hours getting there. One way to really expedite this tuning process is to use an air/fuel ratio meter like the one from Innovate. It offers a data-logging feature that is invaluable in setting up your air/fuel ratio tuning parameters based on rpm and load.