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Pro Tuning on a Shade Tree Budget


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.

bulletChip Upgrades
This type of upgrade is a downloaded fuel map into your factory ECU to improve the performance of your bike.
bulletPiggy 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.
bulletEngine 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.
bulletECU 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.
bulletAuxiliary 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.
bulletDo-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.
bulletRetro-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.

As you can see, there are quite a few ways that you can alter the fuel map of your EFI system. For the average rider Chip Upgrades and Piggy Back Computers are the most viable way of upgrading your motorcycle. For race bikes, you are limited by the rules of the sanctioning body or your own engineering skills as to the extent of change you make to your EFI system. You should be able to make an intelligent decision on the best way to upgrade you bike after looking at our “Upgrades Summary” table.

Modifications to a stock motorcycle is a risky proposition. Modern motorcycles are generally very well tuned from the factory. While proper changes to an engine can result in significant power increases, the owner of the motorcycle must ultimately assume responsibility for the changes made. The author does not endorse or condemn any of the modifications listed in this article, nor assumes responsibility for changes a rider may make to his motorcycle based on this information. Should you be a true motor head, enjoy your new found knowledge and the horsepower potential that comes from applying the knowledge.

Upgrades Summary Table

Although this information is aimed a Harley-Davidson EFI systems, we've actually included a few specific pieces of information for Yamaha's line of cruisers.



Appropriate Use



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


 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.





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.

About the author
"Steve Mullen has been successfully racing various 2 and 4 wheeled motor vehicles for over 30 years. Success with motorcycle racing includes one national drag racing event win and two land speed records. He has written motorcycle performance articles for the past 6 years. His current project is a home built fuel injection system including custom designed throttle body and special computer code for several special build ECU's (electronic control units). On weekdays you will find Steve designing large computer systems. On the weekend you'll find him applying this computer expertise to running his Dyno Rental business and assisting riders in tuning sport bikes and cruisers. He also maintains a popular web site specifically aimed at improving the performance of V-twin motorcycles. You can visit the site at If you need assistance in tuning or modifying any EFI equipped motorcycle you can contact him through the web site.

Below you will find an extensive resource list on general EFI topics, aftermarket EFI systems and Harley-Davidson EFI upgrades. The author may not agree with information contained in some of these WEB sites, nor endorse the products listed. The information is provided as a service to readers to assist them in their performance projects. (
Taylor Marine MAD EFI (
MegaSquirt DIY-EFI (
MegaSquirt Discussion Group (
MegaSquirt FAQ (
Simple Digital Systems (
Techlusion TFI (
Dyno Jet PowerCommander (
S&S Cycle (
Daytona Twin-Tec (
Horsepower Inc. (
Motec (
Yoshimura Research (
Whitek EFI (
RB Racing (
Muzzy (
Dakota Kid (
Gerolamy Company (

Table of Contents
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Modification, Installation, Maintenance and Tuning Index  will help you find most of the information you want on one page.

How to get Professional Tuning Results at home
Testing the Innovate Motorsport LM-1 portable air fuel meter

Profession Tuning on a Shade Tree Budget

Veypor VR2 Data Logger and Instrument Panel
Video Installation and Demo
Purchase VR2

Engine Performance
How to Build a
TC96 2007 Engines
TC88 70HP Stage1  
TC95 128HP Stage 3
TC95 100HP Street
TC96 2007 Stage 1/2
EVO 64 HP Stage 1
EVO 74 HP Stage 2
EVO 82 HP Stage 3
EVO 95 HP Stage 3
883 to 1200 Upgrade
Shovelhead Modifications

New EFI for EVO and TC

Performance Gallery
Horsepower Gallery
Evolution 80
Twin Cam 88/95
Evolution Unlimited
Sportster Unlimited
Drag Strip Gallery
Land Speed Racing Gallery
CV Carburetor
Modifying the CV carb
Tuning a CV carb
Selecting a cam
Install a TC 88/95 cam
Install a Big Twin cam
Install Sportster cams

Camshaft Specifications
Twin Cam

Exhaust Systems
EVO Exhaust Testing
TC Exhaust Testing
Khrome Werks AR100 test
Making Drag Pipes Work

Shop Manual
Carburetor Troubleshooting
Finding Manifold Leaks
Cylinder Heads
Pistons and Cylinders
Belt Drive
Shop Manual Appendix
$20 Bike Lift
Plug Wires
Spark Plugs
Engine Tuning
Nitrous Oxide
Motor Oil
Stutter Box
General Information
WEB Links
Buy Books and Manuals
Performance Calculations
Estimate Horsepower
Estimate 1/4 Mile Time
Estimate Top Speed

Engine Displacement
Exhaust Length
Gear Ratios
Air Density

The Nightrider Diaries
The ramblings of a genius a, a madman and something in between.

Where is Sifton Cams?

Autocom Active-7 tested

Harley-Davidson EFI
-EFI basics explained
-EFI modifications explained

183 HP, 2 carbs, 2680cc

Copyright 1997-2006  Stephen Mullen, Oldsmar, FL -+-