03-16-2015, 10:49 AM
As a retired scientist, let me add my two cents:
Dyno's do not directly measure horsepower, they measure torque in foot pounds. Horsepower is then CALCULATED and displayed by the century old formula below:
Horsepower = torque (in Ft Lbs) * RPM / 5252
On any dyno chart, horsepower will ALWAYS equal torque at 5252 RPM and the two curves will cross, with horsepower usually exceeding torque beyond 5252 RPM. Bad news for Harleys and other cruisers that top out at 5200 RPM. Their horsepower can never exceed their torque numbers.
If you see any dyno charts that do not cross at 5252 RPM, they are bogus. You can look up where the 5252 number comes from on the web. It is a "units" conversion factor.
Looking at the formula again, you can make bigger horsepower numbers by increasing either torque or RPM above 5252 RPM. That is why GP racers are turning close to 20,000 RPM. Friction losses reduce torque, so there are limits in practicality.
One Very Important point - gearing: Gearing multiplies torque. The "lower" the overall gear ratio, the more torque applied to the rear wheel. Engines that can turn high RPM can be geared lower and apply monstrous torque at the rear wheel. That is why small displacement, high-revving motorcycles can out accelerate big-block low revving bikes. Soichiro Honda figured this out in the 1950's. He obviously got an A in physics class.
I have seen many quick Harleys at the drags, but they usually get overtaken by high-revving bikes when the tires finally hook up and the revs get higher. Don't think I am a Harley hater, I have owned 4 of them and their low-revving power characteristics please many people.
BTW - Kevin Cameron is a class act. As busy as he is, he always responds to my emails.
Dyno's do not directly measure horsepower, they measure torque in foot pounds. Horsepower is then CALCULATED and displayed by the century old formula below:
Horsepower = torque (in Ft Lbs) * RPM / 5252
On any dyno chart, horsepower will ALWAYS equal torque at 5252 RPM and the two curves will cross, with horsepower usually exceeding torque beyond 5252 RPM. Bad news for Harleys and other cruisers that top out at 5200 RPM. Their horsepower can never exceed their torque numbers.
If you see any dyno charts that do not cross at 5252 RPM, they are bogus. You can look up where the 5252 number comes from on the web. It is a "units" conversion factor.
Looking at the formula again, you can make bigger horsepower numbers by increasing either torque or RPM above 5252 RPM. That is why GP racers are turning close to 20,000 RPM. Friction losses reduce torque, so there are limits in practicality.
One Very Important point - gearing: Gearing multiplies torque. The "lower" the overall gear ratio, the more torque applied to the rear wheel. Engines that can turn high RPM can be geared lower and apply monstrous torque at the rear wheel. That is why small displacement, high-revving motorcycles can out accelerate big-block low revving bikes. Soichiro Honda figured this out in the 1950's. He obviously got an A in physics class.
I have seen many quick Harleys at the drags, but they usually get overtaken by high-revving bikes when the tires finally hook up and the revs get higher. Don't think I am a Harley hater, I have owned 4 of them and their low-revving power characteristics please many people.
BTW - Kevin Cameron is a class act. As busy as he is, he always responds to my emails.