Chip Beck Explains HP vs. Torque for Mr. Ferret

[thessler3_imp]

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 * 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 final 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.

BTW - Kevin Cameron is a class act. As busy as he is, he always responds to my emails.

[Lord Popgun]

Here is a link that shows where the 5252 comes from: http://www.epi-eng.com/piston_engine_tec...torque.htm

Also, I am not a scientist and don't play one on TV, just posting the link

[cbdtran_imp]

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 * 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 final 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.

BTW - Kevin Cameron is a class act. As busy as he is, he always responds to my emails.

no - go google HP and torque chart, it very much depend how engine is designed, they don't always crossed at 5252

[Lord Popgun]

CB,

You're going to have to explain that one as every scientist and physics expert on Earth says it does. Look at the formula again and tell us how it cannot cross there. Look at the link I provided for more info, or read the post by the SCIENTIST above.

[DGShannon_imp]

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 * 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 final 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.

BTW - Kevin Cameron is a class act. As busy as he is, he always responds to my emails.

no - go google HP and torque chart, it very much depend how engine is designed, they don't always crossed at 5252

no - go google HP and torque chart, it very much depend how engine is designed, they don't always crossed at 5252
As he said, you may find charts that don't but they are bogus. The 5,252 comes from a mathematical formula. The two lines absolutely must cross there. It would be like saying that Pi isn't always equal to 3.14159

[the Ferret]

Mmmm pie. I like warm peach the best with vanilla ice cream.

[thessler3_imp]

Somebody mentioned Pi R squared

Pie are round, cake are square

Thought that should be cleared up.