I always wondered why torque and horsepower cross at 5,250 RPM's so today I googled it.

http://www.motorcyclepowersportsnews...s-talk-torque/

The typical chassis dyno measures how quickly the test bike can accelerate a heavy steel drum – so it’s actually measuring torque (acceleration). Horsepower is then calculated by plugging the values of torque at various rpm into this formula: (Torque x RPM) ÷ 5,250 = Horsepower.

 

I've had these discussions before, it isn't that cut and dried. If it was then every bike that made x tq would make x hp. It doesn't work that way. Seems like it would but is doesn't.

 

Looks like simple math. Maybe someone else can weigh in and tell us why tq and hp always cross at 5250.

 

Just look at any of the FuelMoto dyno charts to see it and this to help explain http://www.largiader.com/articles/torque.html or any other source like http://www.edmunds.com/car-technolog...on-torque.html. I think most use 5252 as the constant.

 

It's been that way since I trained as an engineer in the '60s. Some things don't change. 'Tis the case that torque creates power. Amen. 5252 is closer to the mathematical result. Give thanks to James Watt.

The value 5252 is a constant, in other words a product of several numbers multiplied together. Unfortunately the internet is useless in answering basic stuff such as what the full formula is. Now where are my college notes.....

I only ever tested engines on a brake, not a dyno drum, even a V12 R-R Griffin. Impressive numbers, especially when adding water/methanol at full throttle!

 

Oh the software is written that way, but why does my truck make 397 hp and 750 tq and a another engine make 525tq and 560 hp? And 1 hd engine make 110hp and 125tq and another hd make 135hp and 125tq?

 

Depends on WHERE the engine makes its power. Tq TIMES rpm.

Torque is measured at a specific rpm. Motor 1 makes 100ftlbs at 2000 rpm. Engine 2 makes 100ftlbs at 4000 rpm. Plug in those numbers to the formula.

The numbers you listed are PEAK. The 2 engines you list make their peak at different places.

 

Hmmmm...you might be referring to max torque and and max HP. Most specs will always give you those and they will most likely be different. However, using the formula, you can calculate the HP at that max torque given the RPM at that torque, like the HD Big Twin specs.

The formula also says the torque and HP will always be the same at 5252 RPM. That is where those two lines will intersect on any dyno chart.

 

The rpm where the peak is achieved doesn't matter because the lines don't have to be flat, they can be convex or concave. I have had this same conversation before. It's just not cut an dried as a simple math equation. If it was then every bike that made peak tq @ 3000 rpm and had x tq at that peak would have the exact same hp at the exact same rpm as the other bike.

 

HP=(TQxRPM)/5250. That's why they cross at 5250