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Don't let the Harley heat monster ruin your riding.
Reduce  Engine Surging
Improve Throttle Response
Reduce Engine Ping


HD 2007/2008 Engines

High Heat on 2007/08 HD engines

HD 2007/08 Performance Recommendations

Cool your exhaust temperature with the Wide Band O2 upgrade for 2007/08 HD

Harley Camshaft Specification Tables

HD Twin Cam Engine Builds
TC 128 HP 95 CID
TC 100HP Street Engine

The basics of Fuel Injection explained

Rammer Performance Air Cleaners
TC Performance Heads 100+HP

Pro Tuning on a Shade Tree Budget


How to Richen a Narrow Band O2 Sensor

A narrow band O2 sensor (NBO2) essentially only understands a 14.7:1 air fuel ratio (AFR). Here is a little trick that can be used that will richen the AFR to approximately 14.2:1. While this is still not an ideal AFR for idle and cruising, it is an improvement. These can be built for a very low cost with a few parts from Radio Shack or any other electronics parts supply.

Removed Building the NBO2 Richen circuit

In the Harley-Davidson O2 sensor wiring harness, the Blue wire is the (+) or sensor signal wire. The Gray wire is the (-) or ground wire. excess voltage into the gray wire. This also keeps the divider circuit very small. It should be built as an "inline" circuit.

The A resistor is a 2x ohm value , the B is 1x ohm value making a 2/3 voltage divider. Sorry, the values are proprietary, but with a little experimenting you can come up with some similar values.

The "package" should be put together with barrel crimp connectors on the O2 sensor side. After putting it together, it should be placed in heat shrink tubing to form a vibration resistant, weather tight package. The pigtails can be butt jointed or used with quick disconnects. Adding a wire sleeve around the package after installing it on the wiring harness makes it a very neat, nearly invisible package.

This device is covered by US Patent Law. Any commercial venture to manufacture, sell or distribute this device without appropriate licensing will be subject to legal action. We have no desire to prevent individual riders from building their own DIY circuits. But commercial ventures must obtain appropriate licensing.  
Special Notes on the HD NBO2 sensor

You should never solder a O2 sensor wire because the sensor "will breathe" through the cable. The acceptable method of splicing or repairing O2 wiring is with crimp connectors. This information was from Bosch Technical Staff in Europe. Here is the technical description of why you do not solder the connections on the O2 sensor side of the updated wiring.

The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors insulation and have no vent hole.

It's hard to believe, but the tiny amount of space between the insulation/wire and through wire insulation provides enough air to seep into the sensor (for this reason, grease should never be used on O2 sensor leads/connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to eventually fail.

A special thanks to Kristian Heidenfors for all his help and research on the HD Bosch O2 sensor, testing the voltage divider circuit and additional help on SE Race Tuner..

Voltage Output from a typical narrow band O2 sensor

The accurate range for narrow band O2 sensors is the .400v to .800v or the 15.0:1 to 14.2:1 AFR ranges. Once the fuel ratio is outside these limits, the accuracy of measurement rapidly changes. This is why narrow band oxygen sensor are considered a 14.7:1 AFR voltage switch.

The voltage divider works by taking advantage of the accurate range of the O2 sensor and some simple electronics to allow .750v output from the O2 sensor to look like .500v to the fuel injections system.


Recommended Upgrades for 2007 HD Twin Cam engine


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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 -+-