Fuel Atomization
Some people insist that starting the atomization process higher up in the intake manifold in a carbureted induction system increases the charge density of the air/fuel mixture, and improves the inertial ram effect for increased power. Others argue that since EFI doesn't rely on a carb signal at low rpm, it will therefore produce more torque. According to David, both schools of thought are correct. However, injector placement is a very important factor in the debate. "I agree completely that there are benefits of atomizing fuel high up in plenum. Injector placement, angle, and timing are all very important in EFI," he explains. "If they're not optimized, you could sacrifice peak power compared to a carburetor, but even if they're not optimized, EFI will still beat a carb at low rpm. Some engine builders put one injector up high in the intake manifold and another one down low at the port for the best of both worlds. There's lots of talk about Pro Stock and NASCAR going EFI, and while most people agree that there wouldn't be much of a difference in power, EFI is more forgiving of changing weather and track conditions. In NASCAR, it would allow more control over fuel mileage as well."
XFI
Ever since it was introduced five years ago, FAST's XFI has been one of the most popular engine management systems on the market. As the company's top-of-the-line stand-alone controller, it's packed with features that are still considered innovative to this day. Improvements over its predecessor include the ability to control the air/fuel ratio of each cylinder individually, the option to run multiple injectors per cylinder, and the flexibility to move fuel and spark coordinates to the areas of the maps that need them the most. Small-tire and drag radial racing classes are all the rage these days, and with XFI's traction control system, the unit now makes it easier than ever to both make power and put it down to the ground. "The feature works by monitoring driveshaft acceleration. When it exceeds a set acceleration limit you've already established, the XFI system removes ignition timing," David explains. "The user can control how much and how quickly timing is removed, and how much and how quickly it's put back in once traction is regained. For a drag radial car, a 200 rpm per tenth of a second driveshaft acceleration rate is typical, so once it goes up to 250, the XFI system starts pulling timing out. With XFI's data-logging feature, users can establish their own baseline for driveshaft acceleration. The system can also cut fuel and spark at the same time in order to eliminate popping when using the rev limit or "PA" mode of Intelligent Traction Control. The only additional hardware you need is a driveshaft sensor."