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Hello all new to the site yet to do an intro but can someone please point me in the direction... Looking for a underdrive pulley for a k8 and how to fit it..

Rainy...

There's some on ebay.

Also check the "For Sale" section on these forums.

Just a heads up, UDP's aren't very popular here. The gains are negligible, the loss of the harmonic balancer, and the increased risk of burning out your alternator, or even overheating.... Just not the best idea ever for a mostly stock motor.

just curious. what are the supposed gains and losses of a underdrive pully.
when i put my ze in. my friend gave me one for free off his k8.
and when i had my k8. all his motor had on mine was the pully and it did make his car go faster than mine by a bit.
now its on my ze. dunno if its made a difference. cuz my ze has never been bone stock sence its been in my car.

Ryan wrote:Just a heads up, UDP's aren't very popular here. The gains are negligible, the loss of the harmonic balancer, and the increased risk of burning out your alternator, or even overheating.... Just not the best idea ever for a mostly stock motor.

Thanks for the reply Ryan, Im aware of the pros and cons so to speak was just wondering about the fitment...
personally its just a extra fact finding mission really for peace of mind...

Oh and thanks for the rest of the replys all..

You can find a bunch on ebay but be prepared to do some grinding as they have a 1/2" lip on them that will rub on your engine. Theres a spot where the factory harmonic balancer has an indent to allow this lil protective plate that juts out around the timing pulley where your underdrive wont and youll be cursing at it until you figure out whats up. Atleast thats what I did till I went and forked out the $300 at mazda to get a lighter solid replacement, no rubber bushing, as aparantly they realized it was a design flaw and it fits perfect and is a bit lighter with no accesory consiquences

Either get the Unorthodox brand, or retap the pulley of a cheaper brand, and put in better bolts. I've done alot of research, and didn't find problems with the Unorthodox brand, and alot of problems with the cheap ones (as with pretty much everything on Ebay).
They will give you some HP gains. The more power you're making, the more gain you'll see.
I'm going to put mine on soon, and If I have any problems with slower turning accessory/ water pump pulleys, I'll make smaller pulleys for them. I've read about 3 different people who had Unorthodox UDPs for over 100,000 miles with no problems at all.

well what kinda of problems have people had with the cheap ones?

I've put 10k on my cosmo racing UDP. Never had a problem with alt, water pump, power steering. That was put onto a 115,000 mile k8. The reason I used it was because the stock one fell apart! At the same time I haven't put it on my ZE... the naysayers get to me... There's always the counter argument that less weight = less stress on the rotating assembly.

Not necessarily..... Imagine you're spinning a solid steel cone through the centre, held in the centre.

Now stop it.


Stress? yeah, torsional. Not cool.

But for the tiny difference it makes to weight... meh.

I was considering this but I'm not sure how drastically it would affect the alternator, cause I plan on having a system and everything. But our engines are internally balanced (someone posted a good link a while back, I'll have to find it), so adding a UDP would be like adding a lightened flywheel - as long as they themselves are balanced everything should be okay (hence keep away from the cheap stuff).

Indeed.
The problems people had with the non Unorthodox brand was the trigger wheel seperating from the pulley.
I had only heard of the possibility of either not charging the battery enough, or even causing damage to the alternator, because of slower rotation.
I can imagine, though, that if you spend alot of time idling, and thumping subs, especially with the headlights, and A/C on, you could have problems. When I put mine on, I might look in the junkyard for a pulley similar to the alternator one, but smaller that I can tap to fit. Probably not, though. Other concers are; the steering pump not turning fast enough, so steering could be sluggish, or the water pump not turning fast enough (I've never read of it either thing actually happening).
The benifit will increase as your HP goes up. They say that for every pound you take off the rotating mass, you gain 1HP. I'm sure it's not linear, so when you're making alot of power, you may gain more. I don't know.
In my case, it's one of the last mods, squeezing as much out as possible. With the UDP, Fidanza flywheel, and Aluminum cam pulleys, I'll be taking about 12 lbs. off of the rotation (I haven't weighed the pulleys, or UDP ywt, so it's a guess).

You can also think of it like this; When you're in low gear on a bicycle, it's easier to pedal. If you have lightweight wheels, it's even easier.

fowljesse wrote: You can also think of it like this; When you're in low gear on a bicycle, it's easier to pedal. If you have lightweight wheels, it's even easier.

No not quite, cars have gears and wheels too. If comparing to a bike it would be more like let's take away from some of the biker's metabolic functions in order to increase the energy output to the pedals

Fair enough

This is where I wish I thought enough to weigh my oem replacement for you guys that I got at the dealer... It was lighter (albiet not by much) but solid so no seperation and still powered everything the same. Only downside is cost and I had to wait a week and a half for them to get it from japan


So I was doing my oil today so I figured Ild snap a quick pic, anyone else have a solid factory replacement?