The TCFI Fuel Injection Controller adjusts the fuel curve on the fly.

or years we’ve all had it pretty easy. Fine-tuning a Harley-Davidson’s fuel-delivery system, necessary work after the installation of a new free-flowing air filter or a set of pipes or even after a big-bore job—or just to make that big-twin run its best, involved little more than tearing into the carburetor and changing some jets. And then along came EFI. Now, there’s no argument over the benefits of computer-controlled fuel delivery. It’s way more precise, lots more efficient, and an all-around better idea. Except when it comes to specialized tuning. Faced with a black box and a bundle of wires, we might as well pitch those screwdrivers and box-end wrenches right out the shop window. They don’t cut it in the world of EFI, ECUs and laptop computers.
     What does cut it, however, is the new TCFI Fuel Injection Controller from Daytona Twin Tec. A replacement for the factory Delphi ECU, this control system is the latest word in electronic fuel management. Totally different in design than the Harley-installed system, the TCFI is a true closed-loop system, complete with a really high-tech oxygen sensor mounted in the exhaust pipe. The whole thing mimics the closed-loop functionality of the latest Motec EFI controllers as used in Formula 1 and Indy Car racing. Basically, the unit automatically adjusts the fuel curve on the fly, sensing and delivering optimum fuel values as the bike goes down the road, no matter what modifications have been made to the engine. And that’s just the beginning of the good stuff.

     To really get a handle on what’s happening here, it’s useful to understand a little about the three basic types of fuel injection:
     First of all, there’s the Alpha-N design. This is the simplest, and definitely the most robust. Alpha-N systems deliver their fuel based on throttle-position and RPM, and because of that they’re not at all affected by the sort of manifold pressure fluctuations that might be caused by long-duration/high-overlap cam profiles, for instance. This is the sort of injection control that made Hilborn and Enderle famous. The latest-generation Alpha-N systems incorporate a wide-band oxygen sensor for really accurate fuel metering.
     Then there’s the Speed Density style of fuel control. This system relies on RPM and manifold pressure readings to meter the flow to the injector nozzles. It’s pretty simple to manufacture, reasonably accurate in an open-loop configuration (no oxygen sensor), and it’s inexpensive to install OE. This is the type of EFI that Harleys, and most other motorcycles, come from the factory with, and on a stock bike it’s usually fine. Rideability and fuel-delivery problems crop up when the cam profile deviates from stock, though; erratic manifold-pressure readings send the factory-set ECU into conniptions.
     The third type of EFI control is the Mass Air Flow design, MAF. It’s certainly the most accurate, it will automatically compensate for most engine modifications, and it’s the design used on most new cars. It isn’t applicable to motorcycles, however, since it requires a pretty long air inlet to smooth out the air flow for precise readings—take a look at all that piping under your car’s hood and imaging trying to fit it onto a bike.
     Which brings it all back to the Twin Tec TCFI system. It’s an Alpha-N design, the latest generation complete with that oxygen sensor (and, yes, you’ll have to drill a hole in the rear cylinder’s exhaust pipe and weld on a threaded bung—it’s all supplied). And it’s all worth it. This system automatically adjusts and adapts to any engine modifications, and it replaces all those hours of dyno tuning needed to reprogram a factory ECU with real, on-the-road/on-the-fly tuning. There’s no need to mask-over the hiccups that can be part and parcel of trying to force a Speed Density ECU to deal with those manifold-pressure issues, either. Anyone who’s reasonably computer literate can have the TCFI up and running in no time. All that’s required is to plug the TCFI unit in, replacing the factory Delphi controller, and enter the engine displacement and injector size via laptop—and of course install the oxygen sensor in the exhaust pipe. And then the fun starts.
     While the included software has default settings, after that everything is infinitely adjustable by simply entering new values. A computer savvy guy can get things really fine-tuned, and know it, too, because there’s an included LCD readout module (which can be dash-mounted) displaying the air/fuel ratio at all times and for all conditions. The TCFI’s software comes feature-packed, too. Twin Tec’s totally adjustable ignition control is in here, as are things like built-in datalogging that can be a godsend to tuners. That datalogging is adjustable (via laptop again), and you can save and readout everything that’s happening in the engine for the last half hour. You also can take samples at any interval you choose, clear down to every 1/10th of a second for a true picture of how the engine’s reacting during a hot, full-throttle blast down the street, down the track, or even on the dyno. We’re talking about things like the air/fuel ratio, manifold pressure, manifold temperature, and the list goes on. Cool, huh? Imagine the possibilities. Forget about trial-and-error tuning. With this information you’ll know exactly what needs tweaking, where in the fuel curve it needs tweaking, and why. And you can do it with just a few quick keystrokes.
     And we thought the world of carburetors and jet changes was easy? Forget about it! This is the way to tune, and definitely the way to a sweet-running Harley-Davidson. The Twin Tec TCFI is in-stock now, and your Drag Specialties rep has the info.