Underdrive Pulleys : The Definitive Discussion

[twilightprotege]

Since there has been a bit of interest in the udp's lately, i thought it would be good to dedicate a thread to the pro's and con's of them.

I know a lot of people are against udp's and a lot are for them. Either way, please tell us why!

I for one are for them. they are less than 1/3rd the weight of the stock pulley and they slow down your accessories. the accessories are designed to work at idle, so slowing them down means they just wont work as well at idle, but will work fine when driving normally.

now i know the people who are against udp's say they arent balanced to your engine and you'll damage your engine. i think this is a little bit of a myth and or misunderstanding. until recently, there was quite a big allowance for manufacturing tollerences, which when put in to the engine would be unbalanced and will kill a bearing or worse in no time. this is why harmonic balancers were made, to balance the engine. they were iron (or similar) & rubber.

with better manufacturing in modern cars, the engines are almost completely balanced. harmonic balancers were replaced with just solid iron (or similar) pulleys with very small balancing holes. i know on my pulley i have 2 and they are both very small and close to the centre of the pulley, indicating a pretty well balanced engine.

i accept the slight possibility that and underdrive pulley might kill a bearing down the track, but who cares. it would probably have died anyway. i had a udp on my previous car for 3 years and never had a problem at all.

what i want to know is, with all the failures from the udp's, how many are DIRECTLY related to udp's? i know miata people have had problems with their oil pump or something....when the engine is turbo'd. maybe the turbo (and extra power) was really to blame, but the udp was an easy scape goat??? and those who are against udp's, have you used them before?

and just an option for those who want a pulley but arent sure. you can either have the engine balanced and the new pulley used as the balancer, or a home job - drill a hole 3 times as large in the same spots as the stock pulley. 3 times larger as aluminium is 1/3rd the weight of steel/iron/whatever. obviously not the best option, but hell, if you're so worried, it's an option. i personally will be putting the udp straight on the car when i get it.

so let the discussion begin!

 

[loccusst]

I don't agree on the only at idle underdriving. It should underdrive all the time. That is what it seems to do on my civic. Also if you take the pully to a machine shop they can balance it for you, but if you bought it from a resputable company it should already be balanced.

 

[twilightprotege]

i was meaning idle is the only time underdriving could be an issue

 

[Lord_Zath]

Sweet thanks!

LZ
Z

 

[SpicyMchaggis]

I'm still leary of touching one.

 

[Gen1GT]

I say anything that lowers the rotating mass of the engine is a good thing. The only accessory I even have in my car is the alternator, so the underdrive aspect is worthless to me.

 

[scorch70]

Doesnt Perrin have a lightweight pulley that is normal size (so no underdrive)? Thats the one I am interested in getting. Apparently 85% of your gains with a udp pulley are from the lighter weight of the pulley, not the smaller size.

 

[SpicyMchaggis]

if a lightweight pully is available and is OEM size, I'd buy it.

 

[tonkabui]

let's hypothetically say that i have access to pulleys. how many can i replace in the 3rd gen engines? i know we have the crank, PS, AC, alternator, and water pump. of these, how many are replaceable with a lightweight pulley? no underdriving will occur.

also, there was recent discussion about the magnetic balancing of the stock pulley. how hard is this to replicate with a pulley of the same size but significantly reduced weight and mass?

thanks.

 

[TurfBurn]

I looked into it a bit and my conclusion is this: the magnetic aspect for the CAS is more likely than not a non-issue because of the sensitivity of the sensor and the function of the device.

 

[twilightprotege]

as far as i was aware, the crank, ps, water pump and alternator can be replaced. i doubt the a/c could be. they are usually a complete unit.

has anyone bought the indigo accessory pulleys?

 

[Brian MP5T]

I think the gains not worth it. A lighter flywheel is a much better way to get HP on a street car. The UDP is such a pain in the ass at a stop light. Your headlights dim, the stereo starts to kill the cell.

 

[twilightprotege]

i found with my previous car it was fine at idle, even with the a/c going and 200Wrms amp pumping away. obviously big amps would be bad running at idle, but gives a good opportunity to upgrade the alternator

 

[Brian MP5T]

Upgrading the Alt would defeat the point of the UDP, it would place a harder load on the crank and negate all of the 0.03HP Gain

 

[ZoomThis]

Upgrading the ALT wouldn't increase the load. It is just large and the it has more winding to inscrease the amount of Amps. If there was an increase in the load (or rotational force), it would be minimum. Besides if you have a bumping stereo systems, you already know that you will be taxing the alternator and should have a couple Caps to handle the drain.

 

[JCell]

I got the UR pulley with no prblems whatsoever, only the ac was affected, and not even that much

gains were minimal.....if any

 

[Captain KRM P5]

i'm leery of this as well. Beau from MAM posted a ways back he felt having a UDP on a turbocharged FS was not good for the oil pump

 

[xelderx]

I'll be getting one eventually. I think the problem raised on Turbo cars is real due to the increased stress on the bottom end of the motor, but it's really all theory. There is a good history of oil pump failure on turboed mazdas with UDP's though. The gains from the UDP will be minimal..barely noticable...but when your searching for every last 10th of a second it will help. Also if you have a big stereo why waste your money on a UDP. It's like taking 5 steps back and then half a step forward.

 

[Mad Hatter]

Well it's on with no current problems. No dimming, or choking down at stops, and no noticable gain. I'm sure the ac and summer temps will be the true test.

 

[Brian MP5T]

So the first post should be updated that we all agree...

"Its a waste of MONEY as there are no noticeable HP Gains on the Ass Dyno. Its a pain in the ass to install. It looks pretty"