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Does changing the final drive, change the whp?

I know it changes torque.



I was under the impression that it does, since part of how HP is calculated, uses torque numbers


Changing the gear ratio doesnt change actual whp any more than changing your rims/tires does. Torque is indeed a factor in power, but the other part is how quickly that force moves something.


Hp is a simple formula- Hp is = to Torque x Rpm / 5252.


To make this more clear lets play with some numbers.


Lets go to our good friend, Timmy. Timmy has a car. Timmys car uses engine X! Why did timmy want engine X? Because it sounded awesome. Thats why. Engine X makes 100 foot pounds at ALL rpms, and spins up to 3000 rpms (How does it make 100 foot pounds at all rpms? Its magic. Why doesnt Timmy rev it to 3001 rpms? Because itll break, because its magic). Timmys car also lacks any kind of ratio-changing gearing. Its got a 1:1 from its engine all the way to its wheels. Yup- A straight drive shaft bolted between the engine and the wheels, every time the motor spins once, the drive-wheels spin once. Since we know this, lets calculate how much power Timmy makes to his wheels! Rev to redline Timmy!


100 foot pounds of torque, times 3000 rpms, divided by that magical 5252... Timmys making 57 hp (rounded down). Ok, maybe engine X isnt that Awesome. Dont buy Engine X. Seriously.


Of little surprise, Timmy is a bit disappointed with his power. To help this problem, Timmy installs one of them shmangled differentials in his car. Its got a 2:1 ratio, this means that for every time the engine spins twice, the wheel is going to spin once. This has the benefit of doubling Timmys torque at his wheels. No 100 foot pounds for Timmy, not any more! All the players, they gon' be hatin. Timmy now gets 200 foot pounds at his wheels. Lets recalculate our power Timmy!


Full throttle, 100 foot pounds, times 2 through that differential- Look at all that force Timmy! Bring it up to 3000 rpms.. but whats this? The motors spinning 3000 rpms, but the wheels only going to 1500 rpms. Oh well no matter, weve got 200 foot pounds! 200x1500/5252 and we get!.. Whats this? 57 hp again. Ah well Timmy, back to the drawing board. I hear those Turbo-Encabulators are pretty nifty.







Jokes aside- I hope this was relatively simple enough to understand. You can change the gearing, but you also change the effective rpm in a proportional matter.

Edited by Sideways

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