Gearboxes and BHP

[mikeoxford]

purely random question here does a gearbox effect your final BHP figure depending on what one you have?

or will it only affect the difference between BHP at wheels and flywheel depending on box?

cant see you gaining BHP from a difrent box?

[Tazzy]

i thought it increased torque, but i could be wrong!

(i probably am wrong!) :cry:

[mikeoxford]

i thought it increased torque, but i could be wrong!
(i probably am wrong!) :cry:

i can see how you would get different torques from diferent boxes, yes i think your right.

stil unsure about BHP

[Aragorn]

the bigger and heavier the box the more torque the engine has to apply to simply turn the gears

and since power is directly related to torque and engien speed using more torque to turn the box will mean using more power too

[Dave_Hay]

its a bit of both really, a gearbox saps a fair bit of power but the cog ratios help produce power through the rev range.

gearboxes are really there to provide enough torque to overcome the inertia of the vehicle.

i say power is from crank and torque is from gearbox to wheels. hence you get power losses.

[Stuart]

the gear ratio acctually resuces torque at the wheels eg 100nm at engine and a final gear ratio of 3:1 then you'd have 33nm at the wheels.

the power loss is around 20-30% depending on the box

[Aragorn]

the torque from crank to wheels dont just depend on the FD

it depends on the gear ratio too

you'll supply more torque in 1st than u will in 5th for example

i cant think of the actual relation

its prolly summat like FD devided by gear

[Stuart]

was meant to say "overall" ratio ie FD and gear combined

[CP]

How I look at it is as follows ( Muddy farming boot cam lol)

Torque from an engine is the rotational energy it generates ie. work

Horsepower is a measure of the rate of work.

Gearing cannot make your engine have more power in absolute terms - it is merely a means by which the power is applied to express work. Hence 1st gear mulitplies torque for lugging, 5th gear multiplies horsepower for velocity?

In practise what this ends up meaning is that you have 4 things to consider in your car:
1. Frictional losses in the drive transmission - design , weight, lubrication, tyre and wheel sizes etc
2. Engine type - ie powerful, wide torque band engine = wide ratio gearing and vice versa
3. Application required - ie the relationship between terminal velocity vs acceleration.
4. Strength - you need a transmission capable of dealing with the torque going thru it

[Snowface]

its a bit of both really, a gearbox saps a fair bit of power but the cog ratios help produce power through the rev range.
thats why you get less bhp at the wheels than at the flywheel i guess then.

[Dave_Hay]

and on that note does anyone actually know wtf torque is lol

a rotational force per unit length is how i understand it.

[Stuart]

its a leverage force, which means yes dave you leanrt stuff at uni lol

power is merely a by product of torque and rpm, or rather a rate of torque produced