Upgrading Harley-Davidson EFI engines
You bought your new bike and are looking to improve the power and the sound. You have your new air filter and exhaust system ready to put on the bike, but recognize the need to change the air/fuel mixture to take advantage of the increase in air flow into the engine and exhaust flow out. You begin to sweat profusely as you realize that your latest ride has an electronic fuel injection system. This is uncharted territory for your mechanical skills.
The simplicity of upgrading your motorcycles carburetor(s) to compensate for changing engine components is a thing of the past for many late model bikes. A high percentage of vehicles are now delivered with electronic fuel injection (EFI) as standard equipment or an option. Much to the chagrin of many home and professional mechanics, they find themselves lost when it comes to making the changes required to improve the performance of their bikes. EFI just doesn’t adapt itself to the easy modifications that are possible with carburetors. Riders who were comfortable making jetting changes on their carburetor don’t even know where to start when it comes to their EFI system.
Despite the apparent complexity of EFI systems, the basics of upgrading are surprisingly simple once you understand the basics. You’ll find that you actually have more options for changes and better control of the air/fuel mixture with these systems than the venerable carburetor. The end result of all of this is that your engine will produce better power, provide crisp throttle response and even get improved gas mileage. When you are trying to get the most from your engine, these benefits sound pretty good.
Why modify the fuel system
Any changes in engine components is likely to require a change in the fuel map of your EFI system. The very nature of EFI and its ability to precisely provide the engine with the exact fuel needed is the reason that minor change in components may require changes in the fuel map. While it is a minor regression to EFI basics, I’ll remind you that the EFI computes the exact amount of fuel required for a specific engine RPM and load on the engine.
If you are one of the many motorcyclist’s that make changes to the exhaust system, air filter, camshaft(s) or other engine components, you’ll need to find a way to alter the fuel map.
As you modify your engine, the amount of air that can enter each cylinder is changed. When your upgrades are working properly, they require more fuel. This increase in air into the cylinders (Volumetric Efficiency) is the reason to add more fuel. If fuel map changes were not made, you would end up with a lean running engine. For those of you with V-twin engines and drag pipes we will not get into the reduction in VE that usually occurs at low RPMs.
Types of modifications
There are many ways to alter the fuel curve of your EFI system. We are going to look at several of these in a little more detail and explain how they work. We will also try to point out some of the advantages and disadvantages for each method. While each of the upgrades does alter the amount of fuel the engine gets, many of the common upgrades never really change the fuel map in the ECU.
 | Chip Upgrades
This type of upgrade is a downloaded fuel map into your factory ECU to improve the performance of your bike. |
| Piggy Back Controllers
Piggy Back Controllers connect into the OEM wiring harness to make changes to the fuel map. These devices alter the sensor signal from your engine and “fooling” your factory ECU into providing a different amount of fuel than the real engine conditions warrant. The simplest example of this is that if the factory ECU is told the engine temperature is 30 degrees cooler than it really is, the ECU is going to lengthen the time the fuel injectors are open and provide a richer fuel mixture. It’s actually a simple, but effective way to create new fuel maps. You create an adjusted fuel map in the piggy back system software and it is smart enough to change what the factory ECU senses. The downside of this upgrade is that you never really change the true fuel map that is in the factory ECU.
Piggy Back controllers can also directly extend the time the fuel injectors if they are tapped into the injector wiring. These “pulse extenders” know what RPM engine is running at and the current length of time the fuel injectors are open. |
| Engine Management Software
Software packages like Harley’s SE Race Tuner allow you make any change you want to the EFI ECU. You are actually making changes the internal fuel maps for the EFI. It also gives you control over the ignition and knock sensor. This is the only viable upgrade if you are building a race engine or an above average street engine. The downside to this software is the level of sophistication the user needs in order to take full advantage of all its capabilities. The average rider or mechanic is unlikely to fully understand how to properly use this software package. |
| ECU Replacements
There are a couple of companies that make EFI replacement ECUs. These ECU’s replace the factory EFI and provide their own software to control fuel mapping. These companies may also be in a position to provide electronics to aftermarket motorcycle builders as emission restrictions are tightened. The advantages of these aftermarket ECU’s is that they may be more sophisticated or have more capabilities than the OEM ECU. Case in point is the Magnetti-Marelli unit originally used on HD’s. This unit had limited upgrade capabilities and didn’t lend itself well to performance engines. In some cases, these replacement ECU’s and the management software packages that go with them are similar in price to the SE Race Tuner software. The disadvantage of units like these is the fact that it is a complete replacement for your factory ECU. |
| Auxiliary ECU
These are essentially a second ECU that acts completely independent of the factory ECU, even though it might be controlling the same fuel injectors. These type of upgrades take advantage of the fact that the injectors really don’t care where the instructions come from to put more fuel into the engine. This type of upgrade can only add fuel to the engine, it is not capable of reducing the fuel amount. For race engines or unusual engine configurations (NOS, Forced Induction) this allows a lot of flexibility in building an engine. Multiple sets of injectors can be controlled to compensate for situations where a lot of extra fuel is required. The disadvantage of units like this is that they are pretty much for special purpose racing or over the edge street engines. You are pretty much on your own with something like this, but this is probably not going to be a problem since your engine configuration is probably a one off design. |
| Do-it-yourself (DIY) upgrades
There is always a group of riders that want the least expensive way to increase the performance of their vehicles. By understanding how EFI works, there are a few ways that you could alter the fuel mapping. When you make these types of changes, you are on your own. The types of upgrades that are commonly seen are replacing the engine temperature sensor with a variable resistor, increase the fuel pressure or installing larger injectors. While there are other upgrades that fall into this class of upgrade, we aren’t going to cover them in this article. |
| Retro-fit EFI to carburetor
We spent a lot of time discussing upgrades and modifications to an existing EFI system. But for those of you who want the flexibility of EFI but currently have a carburetor on the bike or a very old injection system, there are EFI systems that can be retrofitted. These systems have varying levels of sophistication. You may have to create your own intake manifold. But in every case, these are not good projects for someone who is not technically inclined or willing to learn a lot about EFI tuning. |
|
Description |
Examples |
Appropriate Use |
Advantages |
Disadvantages |
|
Chip Upgrades |
HD SE Calibration Cartridges
Stage 1
Stage 2
Yamaha Speedstar |
Intake upgrades, exhaust upgrades, kit’ed engine
upgrades |
Calibration cartridges and chip upgrades provide a quick
and simple way to alter a fuel injection when the changes to an engine are
relatively minor and match the component sets specified by the Chip
Upgrade |
The components you can use with your engine are usually
limited to specific parts produced by the manufacturer of the bike. Any
deviation from the listed components may cause a situation where the EFI
mapping is not correct. |
|
Piggy Back computers |
Power Commander
Available for most bikes |
Intake upgrades, exhaust upgrades, Cam changes
Internal engine upgrades |
The PowerCommander is able to change the factory AFR
by altering sensor signals to the OEM ECU. This relatively simple strategy
allows a great deal of flexibility when it comes to creating better fuel
maps for modified engines. These packages allow you to compensate for a
wide variety of engine components. |
The OEM fuel map is never changed. All the PowerCommander
does is "fool" the factory ECU into altering the amount of fuel
the engine gets. Creating custom fuel maps requires a personal computer,
and a certain amount of knowledge of EFI and PowerCommander software. |
|
Pulse Extender |
SE Race Fueler
TFI by Techlusion
Available for most bikes |
Intake upgrades, exhaust upgrades Cam changes, minor
internal engine upgrades |
The TFI can be best described as a pulse extender. It
allows the fuel injectors to stay open longer, thus providing more fuel to
the engine. The TFI does not require a personal computer or any special
equipment to tune the engine. All you need is a screwdriver to adjust 4
variable resistors. Anyone who is familiar with tuning carburetors will
feel comfortable tuning the TFI. |
The simplicity of the TFI is also a disadvantage. Its
ability to alter the fuel curve is limited to richening the OEM fuel curve |
|
Auxiliary ECU |
|
Race engines or exotic engine components |
Trying to run a race engine on the street doesn’t make a
lot of sense, but there are always people who want to do it. One of the
problems frequently encountered is how to make the engine behave at idle
and low RPMs while retain the high horsepower the engine was built for.
This is where auxiliary ECU’s can be very useful. The OEM ECU can be
used to control idle/low/mid range power. By adding a second set of
injectors controlled by the auxiliary ECU, the engine can be tuned for
very high power by creating a second set of fuel circuits. This allows the
use of exotic engine combinations like Nitrous and/or forced induction
systems to have good street manners. |
These are custom engine configurations. When you build
something like this, you are on your own. |
|
Engine Management Software (EMS) packages |
SE Race Tuner |
All street or race engines |
Engine Management Software allows you to modify all
operating parameters in the ECU. In most modern EFI systems, the ECU
controls the fuel and the ignition. The ability to alter fuel curves,
ignition curves, rev limiters and other engine parameters is the ultimate
for fine tuning a performance engine. |
These packages tend to be expensive and very complex. In
many cases the EMS packages may have some "canned" engine
combinations predefined to help the user. But like the Chip Upgrades,
these canned engine combinations assume that your components match their
list of parts.
Despite these issue, Engine Management Software is the
best way to upgrade an existing OEM ECU. Devices like the PowerCommander
and TFI will never be able to give the required control over the EFI and
Ignition systems. |
|
ECU Plug Replacement |
S&S VFI
Daytona Twin-Tek
Yoshimura Research, Yamaha Speedstar
|
High performance street or race engines |
Plug replacement ECU’s are intended to improve the
flexibility of OEM factory ECUs or provide easier tuning than factory ECUs.
These plug replacement ECUs are typically sold with EMS software included. |
These systems have the same disadvantages as EMS plus the
added cost of the new ECU and the time to install the electronics. |
|
New ECU |
MegaSquirt
MoTec
Muzzy |
Race or exotic Engines |
New ECUs are best suited for race engines or street
engines with exotic components that can not be tuned using other methods.
These packages provide excellent flexibility in designing a performance
engine requiring a custom fuel system.
These type of systems can be used to upgrade an existing ECU or can be
used to retrofit a carburetor bike to fuel injection. |
When you get an ECU like this, you are pretty much on your
own. Don’t count on a lot of help from the ECU vendor or your local bike
shop. These packages assume you have a good working knowledge of EFI. You
might end up fabricating parts or finding specific components required to
make the EFI work the way you need it to. |
|
DIY Upgrades |
Engine Temperature Sensor |
Low cost upgrade |
The engine temperature sensor probably has the biggest
single effect on the fuel mixture from a tuning potential standpoint. By
replacing the engine temperature sensor with a variable resistor and
setting the "temperature" to create the desired fuel mixture,
you can improve the power. |
You’re on your own here. While fooling the ECU into
believing the engine is much cooler than it really is can dramatically
increase the fuel to the engine, it can be difficult to be sure how much
extra fuel is getting to the engine. The fuel mixture is also richer
across the entire fuel map.
You will also be preventing your gauges from accurately indicating the
engine temperature. This could create a situation where your engine
overheats. |
|
|
Fuel pressure regulator |
Extreme increases in power or small enrichment of OEM fuel map |
Increasing the fuel pressure at the injectors richens the
fuel mixture across the entire fuel map. |
Increasing the fuel pressure provides very little increase
in performance potential of most fuel injection systems. Raising the fuel
pressure from 39 to 42 PSI will only give about a 3-5% increase in fuel
flow. |
|
|
Larger Fuel Injectors |
Extreme increases in power or medium enrichment of OEM fuel map |
Fuel injectors are sized according to the pounds of fuel
per hour they can provide. Once the fuel injector reaches its maximum fuel
delivery, no additional HP will be produced. Installing injectors with a
higher flow rating increases the maximum HP potential for the EFI system.
You can estimate the maximum HP potential of an engine by multiplying the
flow rating of the injector by 2 and then multiplying by the number of
injectors you engine has. Four 25 pound injectors has a maximum potential
of 200 HP. |
Installing larger fuel injectors does not guarantee that
power will go up. There are two situations where installing larger fuel
injectors makes sense.
1. Your engine is not getting enough fuel at high RPMs and
the injectors are at 100% duty cycle. You need larger injectors to make
more power.
2. You want to richen the fuel map and do not want to use
some of the simpler or more cost effective ways to do this. |
