how do underdrive pullies work??

[jmd2914]

alright i put some on my car and i can feel a differance. i know that they create less drag and thats how you get hp but how do they create less drag? im curious

 

[maverick0716]

It doesn't spin all the accessories as fast, so therefore it free's up more hp.

 

[jmd2914]

could you elaborate? i still dont get it? ( i know its a noob question, but its something that i never learned about before)

 

[maverick0716]

Accessories like, alternator, waterpump, etc...take power to run. If you slow down how fast they are turning you'll gain hp....it's called "parasitic loss" where one or more things (the accessories) live off of the host(the crankshaft) and they make it harder for the "host" to do it's job (turning)

 

[TRWXXA]

Think about riding a bicycle. You can shift it to a high gear ratio (big crank gear with a small rear wheel gear), and turn the rear wheel very fast for only a few revolutions of the pedals, but you need to put out A LOT of effort to do it.

If you shift to a larger rear gear and smaller crank gear, you'll pedal quickly and not spin the rear wheel very fast. You won't be travelling very fast, but it takes almost no effort.

It's the same way with the underdrive pullies. Large pullies on the accessories with a smaller crank pully are easier for the engine to turn -- less horsepower wasted.

However, you will not be getting very efficient output from those accessories -- less power from your alternator, less power to your power steering, etc.

 

[maverick0716]

Think about riding a bicycle. You can shift it to a high gear ratio (big crank gear with a small rear wheel gear), and turn the rear wheel very fast for only a few revolutions of the pedals, but you need to put out A LOT of effort to do it.

If you shift to a larger rear gear and smaller crank gear, you'll pedal quickly and not spin the rear wheel very fast. You won't be travelling very fast, but it takes almost no effort.

It's the same way with the underdrive pullies. Large pullies on the accessories with a smaller crank pully are easier for the engine to turn -- less horsepower wasted.

However, you will not be getting very efficient output from those accessories -- less power from your alternator, less power to your power steering, etc.

Same goes for rear gears on cars actually. That's why people say it multiplies torque.

 

[TRWXXA]

Same goes for rear gears on cars actually. That's why people say it multiplies torque.

That is what, in the education professions, is called, "correlation"!