Submitted by: Terry1955

For all the people that don't quite understand why you need a Race Tuner (SERT) or Power Commander (PCIII USB) for your Harley please read this. This was not written by Harley (who makes the SERT-Race Tuner). I favor the Race Tuner but will concede that the PCIII is also a good piece of equipment. But PLEEEEEEEEEEEEEASE...Don't use the HD download


Why EFI Vehicles Need To Be Tuned
The need for "re-mapping" a fuel injected bike only arises when internal and/or
external engine components are replaced with non stock components, i.e. air
cleaners and exhaust systems. When components are changed on an engine to
any non stock or "performance" part you alter the way that engine moves air in
and out, thus altering the Volumetric Efficiency. If the V.E. is altered the stock
ECM fuel settings continue to deliver fuel at a base-line rate unaware that the air
delivery has changed. With the fuel delivery unchanged and the fact that this
engine is receiving more air there is a lean condition created that will most likely
cause engine damage due to higher heat levels in the combustion chamber. A VTwin
engine is just that, two separate cylinders in a "V" configuration which
generally speaking will cause these cylinders to flow air at a different efficiency
rate. This effect is mostly caused by a non tuned exhaust system that flows air at
different rates from front to rear thus changing the volumetric efficiency.
With the advancements and complexity of today's fuel injection systems
simplicity is not necessarily advantageous. The need to compensate for fuel
delivery to a modified engine ideally would be performed by the original engineer
or programmer of the ECM since they would be the one most knowledgeable on
this system. Since this avenue is not available to the average consumer, a
method of putting a "Band-Aid" type programmer (HD Download) to compensate
for the modifications is the easiest solution, however it is not necessarily the best.
Installing a "Band-Aid" on a system with this complexity can sometimes create a
whole new realm of problems that the original engineers could not have
anticipated.
The Dyno Jet Power Commander unit with it's 126 fuel adjustment cells and 126
spark timing cells offer simplicity that cannot always compensate for the high
demands of a modified V-Twin engine. Especially when the cylinders have a
different V.E. rate, this also offers a "Band-Aid" solution at best.
The H-D EFI Race Tuner Kit offers 220 Volumetric Efficiency adjustment cells for
each cylinder along with an Air Fuel Ratio (AFR) adjustment table that has an
additional 120 cells for a total of 560 fuel adjustment cells. There are also 220
cells for each cylinder to compensate for spark timing, fuel enrichment cells for
cold start and cranking enrichment for easier starting. With these extra tables and
cell adjustments there are over 1000 adjustments that can be made. Also
consider the advantages with having the ability to set your idle mixture as well as
idle speed and having access to your own rev limiter which is adjustable from
4000 to 7500 RPM.