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Sportster Motorcycle Engine Conversions Advice, questions, and tips for 1200, 1250, 1340, 1450 etc... for Sportster and Buell motorcycle engine conversions

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90" engine, angle, cams, daily

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  #11  
Old 4 Weeks Ago
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Originally Posted by groovemeisterus View Post
Think might be a conversion issue on calculation from HP = TQ * RPM.

TQ = HP / RPM and at 47HP at 3000RPM is a very low number.

Maybe TQ equals RPM / HP ?
Did a quick search and equation I found shows to add 5252 in equation ?

Mathematically, horsepower equals torque multiplied by rpm. H = T x rpm/5252, where H is horsepower, T is pound-feet, rpm is how fast the engine is spinning, and 5252 is a constant that makes the units jibe. So, to make more power an engine needs to generate more torque, operate at higher rpm, or both.

Maybe not. 47 HP at 3000 RPM doesn't work with this equation found above either. Number is way too high.

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  #12  
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Found a online calculator for reversing to get TQ.


https://powertestdyno.com/how-to-calculate-horsepower/






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  #13  
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Originally Posted by groovemeisterus View Post
So I could use excel and calculate and plot what the TQ curves would be ? And plot the data on and get an idea of what the TQ curve looks like from HP = TQ * RPM ?

Meaning at any given RPM on the Dyno sheet just use
TQ = HP / RPM ?
You took me too literally. Conceptually, power is torque times rpm. It's useful to think of it that way, i.e. the combination of how hard you're pushing (torque) and how fast you're pushing (rpm).

The reason power is important is because torque and rpm are interchangeable. Want more torque? Gear deeper. On the other side of the gearing, you'll gain torque and lose rpm.

Want more speed? Gear taller. On the other side of the gearing, you'll lose torque and gain rpm.

That's why you can pull a wheelie in first gear but not fifth. You've got far more torque at the rear wheel in first gear than in fifth gear. But you can't go very fast. By the time you get up to fifth, you can go pretty fast, but you're not going to be pulling any wheelies. You've traded all your torque for speed.

Therefore, torque and rpm both make an equal contribution to performance. So it's not torque that matters, it's the combination of how much torque and how much rpm you can make at the same time. They're interchangeable, after all. That number, combined torque and rpm, is called power. Power is torque times rpm.

If you divide power by 5252, you scale it to what James Watt's horse could do. That number is called horsepower.

But that's a nit. Conceptually, power is torque times rpm. It's useful to think of it that way.
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  #14  
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Originally Posted by aswracing View Post
You took me too literally. Conceptually, power is torque times rpm. It's useful to think of it that way, i.e. the combination of how hard you're pushing (torque) and how fast you're pushing (rpm).

The reason power is important is because torque and rpm are interchangeable. Want more torque? Gear deeper. On the other side of the gearing, you'll gain torque and lose rpm.

Want more speed? Gear taller. On the other side of the gearing, you'll lose torque and gain rpm.

That's why you can pull a wheelie in first gear but not fifth. You've got far more torque at the rear wheel in first gear than in fifth gear. But you can't go very fast. By the time you get up to fifth, you can go pretty fast, but you're not going to be pulling any wheelies. You've traded all your torque for speed.

Therefore, torque and rpm both make an equal contribution to performance. So it's not torque that matters, it's the combination of how much torque and how much rpm you can make at the same time. They're interchangeable, after all. That number, combined torque and rpm, is called power. Power is torque times rpm.

If you divide power by 5252, you scale it to what James Watt's horse could do. That number is called horsepower.

But that's a nit. Conceptually, power is torque times rpm. It's useful to think of it that way.

Thanks for clearing that up. Understand better now.


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