When activated by the ECM, the fuel injectors spray fuel into the intake tract. High-flow fuel injectors are available for modified engines and are rated based on the pounds of fuel per hour flowed. Although installing high-flow injectors can increase the maximum power potential for an EFI system, it does not guarantee that power will increase. Usually, injectors are not maxed-out until pushed beyond their 80-percent duty cycle. Additionally, fuel pressure can have a major effect on injector operation. Installing high-flow injectors when they are not required can cause tuning problems, so consider starting with stock injectors until it is determined that high-flow injectors are needed. Still, some tuners use high-flow injectors as a tuning aid, but often there are less costly ways to achieve the same results.
EFI Tuning Aids
Several EFI tuning aids are available to the engine builder and tuner to help eliminate popping, stumbling, surging, pinging, flat spots and overheating, which are sometimes encountered with modified EFI engines. EFI tuning aids can be divided into three major categories:
* Downloadable fuel maps (called ECM calibration by Harley)
* Add-on modules
* Map-based reprogrammers (an add-on module may or may not be used)
Downloadable Fuel Maps
Fuel maps are loaded into the stock EFI ECM to optimize the air/fuel mixture and ignition timing for a specific engine parts combination. Both the Factory and aftermarket manufacturers offer downloadable fuel maps. Harley calls their downloads "ECM calibration" and has several different calibrations for various stages of Screamin' Eagle performance kits. Harley's ECM recalibrations are specifically designed for engines equipped with Harley supplied EFI systems (Delphi or Magneti- Marelli). The way the process works is that you first purchase the fuel map from a Harley dealer, and then you pay them to downloaded it into your ECM. Several aftermarket EFI parts manufacturers offer downloaded fuel maps from their website for given engine combinations. Generic downloadable fuel maps are the owest cost method for eliminating theguesswork of tuning an EFI engine with performance modifications.
Add-On Modules
Add-on modules connect in series between the stock ECM and fuel injectors and modify the ECM's output signals before the signals reach the injectors. Most units are adjusted by using a screwdriver to adjust the "pots," which adjust rpm transition points (not the ability to increase the rev limit) and air/fuel mixture. Other add-on modules require entering numbers using a display/button device. Certain add-on modules can only instruct the injectors to add fuel or richen the air/ fuel mixture, while others include the ability to both add (richen) and remove (lean) fuel. Pot-based devices are relatively low cost but have certain limitations as to the range of performance engine modifications they can tune.
Map-Based Reprogrammers
Once your engine enters the 100-plus cubic inch range, or you have made major engine modifications, pot-like devices cannot satisfy the engine's air/fuel requirements. That is where map-based reprogrammers, such as the Harley- Davidson SE Race Tuner, come into play because they have the ability to make virtually unlimited fuel map changes to the stock ECM.
Dynojet's Power Commander is a mapbased reprogrammer that connects in series between the ECM and fuel injectors. The add-on computer stores maps that can be reprogrammed with a personal computer (PC) for a wide range of engine combinations. Fuel, ignition, and rpm values can be changed for both front and rear cylinders.
7. Shown is a new oversize Dual Flow 50mm TB from BC Gerolamy. The Dual Flow 50 is designed for early Big Twin Magneti-Marelli EFI systems and for converting singlebore Delphi systems to dual flow with independent runners. | 
8. S&S Cycle recently announced their new 52mm Single Bore TB for modified 1995-05 EFI Big Twins and 2006- 07 models. S&S says it is compatible with most stock and aftermarket fuel injection modules on the market. | 
9. Add-on EFI tuners, like this potbased Screamin' Eagle Race Fueler, connect in series between the stock ECM and fuel injectors and modify the ECM's output signals before the signals reach the injectors. Pot-based tuners are relatively low cost but are limited as to the range of engine modifications they can tune. Courtesy of Harley-Davidson. |