underdrive pulley question

Do the stock belts work or do I need a smaller belt (IE: on 3sx they offer the pulley with the belts. Are these stock size belts or specially made?)

underdrive you need diff belts..

Isn't installing a UDP kind of gambling with the life of your engine? I've known a few people who installed one on their NA, but not many who put them on the TT's. You know, bearing failure and all...

Isn't installing a UDP kind of gambling with the life of your engine? I've known a few people who installed one on their NA, but not many who put them on the TT's. You know, bearing failure and all...
Thats a myth. Never ever been proven to cause bearing failure. Bearing failure is caused by lack of lubrication. There are PLENTY of people over at 3si TT and NA that have been running a UD or LW pulley for 30k or even a lot longer with no issues.

Well I own an NA. The debate on underdrive pulleys is always gonna be discussed. I can see why people would say they hurt the engine, but there's an entire page somewhere talking about it... and how underdrive pulleys don't hurt the engine. I'll take the gamble and use one though. I feel like many 3S owners reccommend it anyway, I don't use high powered subs or anything.

There have been people that have had problems with them too. Don't UDP's put more stress on the crankshaft and cause more wear to it than necessary? I was always under the impression that the increased vibration was the problem with the UDP's.

yeah.. they dont "balance the harmonic's" in other words they dont have the little rubber ring that keeps the crank shaft from vibrating.. its like hitting a Bat on a metal pole your hands are going to hurt from the vibrations if you have a rubber or somthing that will reduce the vibrations it it wont hurt, or shake for that matter, as bad.... wow i suck at explaining this.. haha

p.s. i have an underdrive and love it!!

Its been said that all the stock crank pulley does is quiet the belts. They call it a harmonic balancer but any decent aftermarket crank pulley you buy is going to be balanced and its not going to cause any unnecessary "harmonics".

Jeesh, this just keeps coming up again and again...

Have you guys seen those failure "s" curves? Where # of failures are plotted against millions of operating hours?

What happens is an engineer in the company plotted the incident cost of repair during the warranty period against the cost of a harmonic balancer, and decided that it was cost harmonic balancer was cheaper.

But this cost was amortized over cost of producing X number of engines over X million of operating hours.

Now it is true that removing the harmonic balancer does incrementally increase the probability of bearing failure... So does adding a high performance exhaust, open element intake, and any other performance modification.

If fact, almost any other performance modification has a larger affect on bearing failure then the deletion of the harmonic balancer (since really, the harmonics are just transferred to the belt to damp, in which case belt failure is really what you should be complaining about).

If you were really that concerned about reliablility, don't mod your car.

(BTW: I don't like under-drive pulleys it's annoying to have your lights dim at idle)

My lights already dim at idle. Sometimes the idle drops lower than it should so the load on my alternator isn't as big. But it's not a big deal to me.

My lights already dim at idle. Sometimes the idle drops lower than it should so the load on my alternator isn't as big. But it's not a big deal to me.

that's probably more to do with your IAC/ISC than your crank pulley.

I say go lightwieght, not underdrive, that way you can use stock belts and your alternator wont be affected, gain is supposed to be almost the same.

There is actually a underdrive pulley on my Talon. I have no issues with dimming lights.

Well I'm aware that the lower idle is due to the IAC, I've replaced it twice and seen improvement. But I doubt an underdrive pulley will affect the dimming lights that much, especially to the point that I would mind... the car doesn't sit at a stand still for very long anyway:)