Just a bit curious....
1. What is an underdrive pulley (kit?)?
2. How does this improve performance, and by how much?

Thanks.

 

an underdrive pulley is slightly bigger than stock so that it spins the accessories slower. basically, it takes a certain amount of hp to spin the accessory once. so if it spins leess rpms, then it ends up using less power than normal. also, they are usually a little lighter. as a warning, ive heard of the crank pulleys tearing up the motor, as it doesnt remove vibrations like a stock one does. expect a couple of horses from these. not groundbreaking, but every little bit helps.

 

the vibrations are due to poor balance (from crappy machining and crappy testing). if buying pulleys I would recommend getting it from a brand name like AEM because they have done so many of them.

 

the vibrations are from the harmonic vibrations of the reciprocating mass of the engine moving up and down. a stock crank pulley has rubber in it that is designed to dampen the vibrations. ive heard from people who had the unorthodox racing pulleys and had that problem, so its not all about the quality of the underdrive crank pulley.

 

yea they dont have harmonic balancers...or they are not harmonicly balanced...its one or the other but thats the reason they dont stop and cause vibrations

 

oops.

 

yup. thats why going with a brand name you know it will be tested and balanced.

 

unorthodox racing is one of the best ones on the market. and i t still has problems. its a design flaw, not a manufacturing one.

 

they are obviously no good since there are problems and you say there is a design flaw. That would seem to indicate that it is an inferior product.. how do you mean they are one of the best on the market?

I've already written this in 2 other posts.. crappy testing is one of the factors! Proper testing will help produce better products that will work as intended. Obviously, since the auto manufacturer could produce a pully that worked.. it is possible to do it. It just requires testing... and obviously fixing the problems that are found from testing.

 

if you thiknthe auto manufactures make the best parts for performance, then you are in the wrong forum. there is a reason we replace parts on our cars. when manufacturign cars, the automakers have to appeal to more people than just enthusiasts. in turn, some parts of the cars have compromised some performance in the name of longetivity and a smooth ride. i dont mind a little vibration from my polyurethane motor mounts, but the little lady that has a civic that lives next door to me probably wouldnt have bought it if it vibrated like mine does. the same goes with other parts, like i dont mind giving up a little longetivity in my motor to have a turbo on it. again, the little old lady would rather have a slower car that will last a long time. some people dont mind compromising the longetivity of their engines by changing the dampener pulley to a solid steel/ or aluminum one that doesnt save the main bearings by reducing the vibrations of the crankshaft in the hopes of gaining some performance by reducing rotating mass and parasitic drag on the engine. there are performance options though. check out fluid damper, they make an aftermarket one that still has a provision for reducing harmonic vibration. its the fact that the engine itself is not possible to completely balance and the pulleys are solid. not that the pulley is causing the vibration.