It wasn't really the best of times or the worst of times, but in the hot rodding world, the mid-'80s witnessed a peculiar convergence of euphoria and pandemonium. The decade prior had seen the heinous castration of muscle cars, as Chevy's flagship Corvette was emasculated to a pathetic 165 hp come 1975. Engineers made great strides, however, and the horsepower of performance cars was creeping back up near the 300 mark by the late-'80s. Interestingly, while some members of the power-hungry enthusiast crowd rejoiced, traditionalists balked at this frightening new technology called electronic fuel injection.
Fortunately, the aftermarket soon stepped in by developing stand-alone engine management systems that took over fuel and spark duties from stock PCMs. The aptly named Fuel Air Spark Technology (FAST) was one of those companies, and since the mid-'90s, FAST has been one of the most prolific manufacturers of stand-alone EFI systems on the market. Vehicles equipped with FAST electronics cover the gamut from 11-second street/strip machines to full-blown race cars kicking out thousands of horsepower. In 2001, FAST became part of the Comp Cams family of companies, and the additional resources resulting from this new relationship has enabled it to develop cutting-edge products at a staggering rate. Released in 2004, FAST's XFI engine management system continues to be a favorite with cruisers and racers alike, and the company's new EZ-EFI system can literally tune itself.
To get educated on the latest in EFI technology and to pick up some valuable tuning tips, we recently had a chat with FAST's David Page. The horsepower race is still full-steam, and with the goodies that FAST has in the works, it's obvious that they plan on being there every step of the way.
As horsepower levels start approaching the 1,000 mark, a standard high-impedance injector will no longer cut the cheese. That's because it's tough to find a high-impedance injector that flows more than 72 lb/hr. After that point, high-flow, low-impedance injectors are a must, which requires upgrading to an aftermarket stand-alone ECU such as XFI. This begs the question, "What's the difference between these two types of injectors?" "Impedance is just another word for resistance. High-impedance injectors have 12-16 ohms of resistance while low-impedance injectors have 2-5 ohms of resistance," David explains. "The drivers in the engine management computer are what actually send the signal to open up the injectors. If you try to open low-impedance injectors with a stock PCM, the extra electrical current flowing through the drivers will burn up the drivers and the computer. A stand-alone system like XFI has much more robust drivers that act like relays, and can easily handle the extra load. Plus, the XFI box itself works like a heat sink to help dissipate the extra heat."
XFI vs. EZ-EFI
With the launch of FAST's new EZ-EFI system to complement its premiere XFI system, the company now has a two-pronged lineup that covers everything from mild street motors to full-blown racing applications. Each system has its benefits, and deciding between the two depends on a number of variables. "EZ-EFI is an entry-level system that's still extremely capable. If you have a naturally aspirated motor, but aren't too familiar with tuning EFI, then the system is extremely appealing," says David. "It includes four 83 lb/hr injectors, which are good for 600-650 hp. Beyond that power level, or with power adders, you probably want to step up to our XFI system. There's definitely a learning curve involved with figuring out how to tune a motor, but it allows for much greater tuning flexibility. If it's not something you want to tackle yourself, there's a large network of professional tuners out there who can help you out."
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."
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."
Granted, the abilities of FAST's EZ-EFI system sound very promising, skeptics will surely question how well it can really tune a motor, especially combinations with big cams. As it turns out, the system works so well that its performance warrants its own sidebar. During development testing, the FAST crew spent several hours tuning a GMPP 572 crate motor with its top-of-the-line XFI system, which netted 630 hp. FAST then replaced the XFI system with an EZ-EFI setup, and the 572 cranked out 630 hp after two pulls. "I was actually kind of embarrassed that the EZ-EFI system did in five minutes what it took me a couple of hours worth of tuning to accomplish. The ECU reacts so quickly that if you experience a lean or rich spike while cruising, you'll actually feel the motor smooth out," says David. Nonetheless, EZ-EFI does have its limits. Since it was designed as an entry-level system, David advises against using it with nitrous or boost. At that point, he recommends opting for FAST's more advanced XFI system. Even so, the limits of EZ-EFI in naturally aspirated applications is quite high, and it can easily adapt to the wildest of combinations. "We put a 227/241-at-0.050 hydraulic roller cam with a 107-degree LSA in a GMPP 350 crate motor, which had a very rough idle when it was first fired up. Within a few seconds, the EZ-EFI system made the necessary tuning changes, and the motor idled perfectly at 900 rpm."
"Most hot rodders are very familiar with a carburetor, but shy away from EFI because they're scared of the tuning process. Consequently, we wanted to develop a true self-tuning EFI system that was very versatile while requiring very little input from the user. The result is our new EZ-EFI system, which literally tunes itself within two pulls on the dyno. The kit includes a 4150-style throttle body, four 83 lb/hr injectors, fuel rails, an ECU, a wiring harness, a wideband oxygen sensor, and a hand-held controller. To keep things simple, EZ-EFI controls the fuel only, meaning that spark advance is still controlled with the distributor. Many EFI systems have the ability to make air/fuel corrections in closed-loop operation by utilizing wideband oxygen sensors. EZ-EFI takes it a step further. Instead of merely making minor corrections to the air/fuel ratio, it actually changes the base fuel map itself. For instance, if an engine needs 10 percent more fuel at a certain rpm, it changes the map instantaneously. The system is pre-programmed to achieve target air/fuel ratios of 13.5:1 at idle, 14.7:1 at cruise, and 12.8:1 at WOT. After installing EZ-EFI, the hand-held controller asks for some very basic engine specs, such as displacement, desired idle speed, and fuel pressure. The user can also change the target air/fuel ratios if necessary. After calibrating the throttle-position sensor, all you have to do is hit a button and fire up the motor. The ECU then starts calibrating the fuel map instantaneously."
"As part of the Comp Cams family that includes RHS cylinder heads and ZEX nitrous systems, FAST now has access to a diverse range of resources that enables us to develop new and innovative products more efficiently than ever before. This allows us to react quickly to changing market conditions and customer demands, and develop crossover technologies. For instance, when GM introduced variable valve timing into its LS-series motors, Comp Cams dedicated tremendous efforts into testing new camshafts for them on the dyno. It was then up to FAST to come up with the electronics to control how to advance and retard the cams. By combining our resources, Comp has developed the valvetrain components to take advantage of the Cam Phasing technology and FAST is developing the electronics to manipulate the cam phasing for maximum performance."
The venerable carburetor has soldiered on because it's simple and performs extremely well. Some people have argued that switching to EFI can be worth a few extra horsepower, but even David is quick to debunk that myth. "If you have a carburetor that's properly dialed in, you may not get any more peak power with EFI. In fact, because the fuel is atomized higher up in the intake manifold, sometimes a carb will make more power," he says. "On the other hand, EFI will make more torque because you can optimize the air/fuel ratio much more precisely at low to midrange rpms. Plus, fuel economy, driveability, and cold-start performance will be improved dramatically, and emissions output will be reduced as well. And let's face it, some people just want the cool factor of having a muscle car with high-tech hardware like EFI."
Unlike carburetors, which continuously discharge fuel whenever the throttle cracks open, injectors squirt fuel into the combustion chamber in short pulses. Although it's rarely an issue in moderate-horsepower, low-rpm applications, proper injector timing is critical in more radical combos where the time required to fill the cylinders with air and fuel is dramatically reduced. "Injector events can't be too long or too short. They have to be just right," David says. "To get a complete charge of fuel into the chamber, the injector pulse should be optimized in relation to the opening of the intake valve. Injector sizing also plays a role, and bigger isn't always better. If your injectors are too big, then their pulse widths will be too short for any given volume of fuel, leading to poor atomization. Our XFI system gives tuners the ability to adjust the injector timing."
Cars powered by GM Gen II, III, and IV small-blocks can have their stock computers tuned with a laptop using software systems offered by several aftermarket manufacturers. Some even have the ability to tune in real time, and use two- and three-bar MAP sensors for forced-induction applications. While the limits of these tuning solutions are extremely high, there's still a point where stepping up to a stand-alone system is necessary. "I'm always amazed at the level of power guys can make with a stock PCM, but stand-alone EFI software is much more flexible and easier to use," David says. "For power-adder applications, you can change the timing for boost or nitrous on fly with a stand-alone setup. Also, the injector drivers are much more robust in a stand-alone system, which makes it possible to run low-impedance injectors or even dual injectors per cylinder. Integrated data logging and traction control capabilities are a huge plus for hard-core racers as well."
Pump and Injector Sizing
Since EFI operates at much higher fuel pressure than a carbureted induction system, upgrading to fuel injection requires greater fueling demands. For naturally aspirated combinations, David recommends selecting a fuel pump that flows 1/2 lb/hr of fuel for every horsepower. In other words, a 1,000hp naturally aspirated gasoline combination needs a pump that can flow 500 lb/hr at working pressure of fuel plus a 10-20 percent safety margin. For forced-induction applications, David prefers fuel pump flow rates of 0.60-0.65 lb/hp plus 10-20 percent. Proper injector sizing can also be calculated in a similar fashion. "Injectors are all rated at a certain fuel pressure, and increasing fuel pressure can bump up the flow rate of an injector. Typically, 42 lb/hr injectors are enough to support 600 hp, because 42 lb/hr multiplied by eight injectors gives 336 lb/hr of flow. Multiply that by 2 to get 672 hp minus 10 percent for safety margin comes to right at 600," David says.
With XFI, users have the ability to run two injectors per cylinder on a typical V-8. Although this isn't necessary in even the wildest of street/strip combinations, it does allow for some extreme possibilities. "Sometimes it's simply a matter of fuel volume, and some motors need so much fuel that two injectors per cylinder is a must. On a V-8, our dual-injector setups can support close to 5,000 hp," David explains. "In other scenarios, having multiple injectors helps optimize the fuel charge going into the port. Sometimes, it's better to run two 36 lb/hr injectors per cylinder instead of one 72 lb/hr unit. Placing one injector up high in the manifold and the other down low by the port improves the atomization process. Engine builders can also experiment with injector positioning. Some like to have the injectors spray horizontally along the roof of the port for improved charge density."
Learning to Tune
Advanced aftermarket EFI systems like XFI are perceived by the average enthusiast to be very difficult to tune. Truth be told, pecking away at a keyboard isn't as intuitive as turning screws on a carburetor. To help novice tuners get acclimated with all the different parameters that can be changed with XFI, FAST offers several resources. "Anyone who's willing to invest the time can learn how to tune a motor with EFI. We include a 2 1/2-hour instructional DVD with our XFI system that tells you how to modify each and every table in the software," David says. "While that alone won't make you an expert tuner, it's a great learning tool. Also, the XFI software is available as a free download on our website, so you can try it out before you buy it. Our tech line is always happy to provide assistance, and there's lots of great information available on online forums as well. Furthermore, based on customer feedback, we are in the process of putting together an XFI training course in the near future, so stay tuned for details."
Let's say you want to run an electronically controlled late-model GM overdrive transmission in your carbureted street machine, but don't know how to get its electronics to work. FAST has developed a solution to this common problem with its stand-alone transmission controller. "This is another instance when being part of the Comp Cams family was really beneficial to product development. By working closely with TCI, we came up with a stand-alone trans controller that can be used with carbureted motors, EFI motors using the stock PCM, or with our EZ-EFI and XFI systems," says David. "The controller interfaces with factory transmissions using application-specific FAST wiring harnesses. By hooking up the controller to a laptop, users have full control over setting shift points, shift firmness, and torque converter lockup. Depending on the needs of the vehicle, tuning can be accomplished based on rpm, speed, gear ratio, or load."
"FAST was one of the first companies to develop an aftermarket intake manifold for GM LS-series motors, and they're available with both 92- and 102mm throttle-body openings. All FAST manifolds feature a composite, three-piece construction that can be easily taken apart for additional porting, and keeps heat absorption to a minimum. The 92mm intake works best with 350-383ci motors, while the 102mm unit is designed for larger 408-421ci combos. We have also recently introduced our LSXR intakes, designed for rectangle-port L92, LS3, and LS7 cylinder heads. This has proven to be a huge hit for engine builders installing these innovative new heads on older short-blocks. On a 500ci LS-based engine, we made near 800 hp with this intake."
"FAST is always working hard to stay at the forefront of the market. Our EZ-EFI system and new LS3 intake manifolds are just a few examples of what's currently in the works. For cathedral-port 4.8-, 5.3-, and 6.0L LS-series truck motors where tight hood clearance isn't an issue, we've just introduced a new 102mm LSXRT intake manifold. It features the same modular construction of our other composite manifolds, but with a few key distinctions. This new truck intake boasts more plenum volume, and its runners are angled more steeply to provide a more gradual transition into the intake ports. Also in the works is our new XIM stand-alone ignition control system. This unit is designed to control the spark in LS-motors that are running a carburetor."