Obtaining consistent dynamometer test results requires disciplined actions when setting up the vehicle and performing the tests themselves.
Following are the areas where you need to pay special attention. It has been a while since I ran a dyno, so I contacted a couple of experts for help: Mike Daniels, owner of Daniels Performance, who is probably the busiest motorcycle chassis dyno trainer in the United States, and Will Fong, sales and marketing manager at Dynojet Research, who has more than 10 years of experience with Dynojet motorcycle chassis dynamometers, the most common dyno found in motorcycle shops worldwide. Their comments are included in this article.
TIP #1: Too Cool for School?
When the drivetrain is less than operating temperature, lubricants are thicker, which increases internal friction leading to reduced power output. Use an infrared thermometer to measure the oil temperature by aiming it at the oil reservoir. Oil temp should be at least 180°F to get consistent results.
Daniels adds: I find it takes about 20 miles of riding to get a bike close to normal operating temperature. 180°F is the minimum oil temperature for most bikes, and 200–220°F oil temperature is ideal. For consistent, repeatable dyno runs, we strive for consistent oil and cylinder head temperatures.
TIP #2: Or is it Hot Hot Hot?
Bikes can overheat on the dyno if they don’t receive enough cooling air, and air-cooled bikes are more sensitive than liquid-cooled bikes. If the last full power dyno run indicated less horsepower than the previous run and you made no tuning changes in-between, there’s a good chance the bike is overheating and needs to cool down before testing is resumed. Make sure cooling air is aimed toward the radiator or engine cylinders.
Daniels adds: Most EFI-equipped bikes richen the mixture and retard the timing when the engine reaches excessively hot temperatures. In most cases, the engine needs to become much cooler to reverse this event so you can start tuning again.
TIP #3: Suspect Conditions
|A rear tire low on pressure can dig into the dyno roller, causing excessive friction and heat.|
Old dynos (1998 and earlier) require atmospheric conditions, such as the wet and dry bulb temperatures, to be measured manually and logged into the dyno program to achieve an accurate correction factor. The correction factor affects every measurement in the test, so a mistake here — intentional or not — alters the results. Therefore, the dyno’s temperature sensor should be positioned in the booth to correctly measure the booth’s ambient air temperature, not the heat coming from the engine.
Fong adds: Our Dynojet 250i models have the weather station built into the side of the dyno, so with that model there is no way to relocate the sensor. I would just mention to verify the weather conditions reading prior to dyno testing. For example, if you measure 50°F in the test booth but the sensor reads 100°F, you know something’s not right. Note that our new electronics (launched in February) will have the ability to locate the sensor where the operator desires.
TIP #4: Low Pressure Problems
A rear tire low on pressure can dig into the dyno roller, causing excessive friction and heat. It robs power and it’s very hard on the tire. Inflate the rear tire to its factory-recommended pressure and inspect the tire for excessive wear or damage before dyno testing. If tire condition is ever in doubt, replace the tire before delivering the bike back to the customer. Never take chances with a suspect motorcycle tire.
Daniels adds: If the tire is getting hot, be careful about how hard and how fast you accelerate the rear wheel during a full power run. Note the tire speed rating on the tire and never exceed it. For higher gear runs at higher tire speeds, make sure the tire is cool before performing a full power dyno run.
TIP #5: Tight Ain’t Right
An excessively tight rear belt or chain will rob power — most noticeably at higher wheel speeds. I’ve seen a tight belt rob up to 10 horsepower. Also, some belts are hygroscopic (absorb water) so their tension will change dramatically from cold to hot. The best advice is to ride the bike or run it on the dyno to warm up the belt and sprockets and then recheck the belt or chain tension before measuring power output.
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