John Lyon, General Manger of Wilkins Harley Davidson in Barre tells a story about his uncle, Alan Wilkins using a stethoscope to diagnosis a motorcycle while riding down the road. Alan would press the scope against the motor as he rode, carefully listening for clues on how to tune the engine.
The stethoscope was high-tech for it’s time and an effective way to gather information. But Alan’s technique of probing a running motor while riding would tell him very little about the tune of a modern, electronically controlled motorcycle: electricity doesn’t make noise.
The dynamometer is the modern-day replacement for the stethoscope, as the tool for gathering data on a running motor’s performance. A dynamometer measures force. Using this measurement, the device determines the amount of torque and power a motor is producing at any RPM.
Last year, Wilkins Harley Davidson purchased a Dynojet 250i dynamometer to improve the accuracy of their tuning work.
Building a Hotter Harley
While 100 plus horsepower is common for modern sportbikes, creating a hundred horsepower Harley is more of a challenge. A stock FXST Softtail produces 57.7 horsepower and 71.8 foot pounds of torque measure at the rear wheel, according to Motorcycle Consumer News tests.
“People think they can get to 100 horsepower by doing a few modifications...read more
“A lot of customers would come in and say that their bikes had been tuned by using a Power Commander or a TTS Master Tune,” said John Lyon. These devices can measure the running performance of motor and suggest an Engine Control Module tuning map to use. “The problem is, these devices have to make a lot of assumptions.”
An ECM map is a set of tables containing air-fuel mixture and sparking timing for specific RPM and throttle positions. The map is specific to the motorcycle and its modifications (exhaust, air cleaner, cams, etc.). Ultimately, the ECM map controls how each system in the motorcycle operates.
The map suggested by a Super Tuner or Power Command is usually lean, Lyon’s said. When a motor runs lean, it runs hot. The hotter a bike runs, the more susceptible it is to damaging pistons and valves. This is especially true when riding the motor hard.
A dynamometer enables a technician to precisely record motor performance. As the technician runs the motorcycle, the device records the throttle position, RPM, air-fuel mixture, output gases and power production. Because the testing is in a known, controlled environment the data is more accurate. The testing results are standardized, which enables tests to be compared, facilitating accurate adjustments over time.
Using a dynamometer, a technical can measure the full range of motor performance and can record more data points. When running a motorcycle in a street environment, the motor has little or no time to operate at the extreme low and high ends.
Mike Bedor, a technician at Wilkins likes the dynamometer because it makes it possible to see what is happening inside the motor. “It takes what’s happening inside the engine and puts it on a display,” he said. “People will continually throw stuff at their bike [to make it perform better], but don’t really know what it does.”
The dynamometer has graphic displays that enable Bedor to get visual feedback showing the exact effects of changes. The dynamometer reports air-fuel mixture and cylinder usage (Volumetric Efficiency) by RPM and throttle open percentage. Using this precise data, Bedor can make tuning adjustments and immediately get feedback on the change.
“When you tune, it’s tuned for the way the bike is running at that time. If you change something – your exhaust or your air cleaner – you change the way the bike is tuned. Even small simple things effect how the bike runs.”
For Harley riders, pairing Screaming Eagle Super Tuner with the dynamometer is the ultimate for performance tuning, Bedor said. The Super Tuner enables him to modify the air-fuel ratio by modifying injector operation, spark timing, and valve opening for each cylinder.
The dynamometer is also a good tool for optimizing fuel economy and diagnosing drive train issues. Using the air-fuel data, Bedor can optimize fuel efficiency without running lean. He can troubleshoot drive train issues by using a negative horsepower test, which measures rolling resistance caused by mechanical components.
The Dyno at Wilkins is equipped with an eddy current load unit to create rolling resistance. The unit enables technicians to simulate street riding by creating varying loads. Technicians can setup test ride scenarios or log winter break-in mileage after motor upgrades.
While Wilkins specializes in Harley Davidson, riders of all brands are welcome to test their bikes on the machine. “Anyone who wants to get their bike done – we’re more than happy to do it,” said Bedor.
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