Underdrive Pulleys

[Quinn]

I am thinking of adding Underdrive pulleys to my '99 Golf GTI. I read something of the sort, that adding the pulleys don't add HP, but it does allow the car to reach higher RPM's faster. So does that add torque to the car? Also does anyone think that this may be an underrated mod? Is there a shelf life to the pulleys, so to speak? I mean do they last as long as the stock pulleys? Just looking for basic insight.

Thanks,

Quinn

 

[the_names_james]

It won't give you any more power, but it'll 'free up' power used when the engine turns the heavier standard pulley, i.e. flywheel hp won't change, but wheel hp will. It'll allow the engine to rev a little quicker.

And yes, it is an underrated mod.

 

[obi_waynne]

The principle behind the underdrive pulleys is to reduce power drain to the alternator and water pump - so effectively these items run slower. You are not so much gaining power as not losing quite so much. The makers build in a certain amount of leeway but on a cold night with the lights, heater, wipers and radio blaring you can max out so if you do it wrong your alternator will no longer deliver enough power - well maintained cars should be OK but the makers play it safe for a reason.

It worries me a little that the cooling is also operating at reduced speed so you really should get an oil temp and water temp gauge fitted at the same time so you can keep an eye on things.

IMHO it's not much of a gain for the effort although it is a very cheap mod. You may look to an electric water pump as a compromise which is intelligently controlled rather than engine RPM dictated so less power is taken from the engine. If you have ever tried turning a water pump over by hand you will realise the amount of effort taken.

 

[Quinn]

Thank you for your input. I think I'll skip this mod due to the fact that it doesn't sound like it's not going to really add any more zip to my car.

Correct me if I misunderstood your replies

 

[obi_waynne]

One way of finding out is to remove the alternator/water pump belt. You've probably only got 60 seconds and I would only do this with a cold engine. One company did this on a rolling road and saw 3bhp increase (obvioulsy with overdrive pulleys rather than nothing there would be even less of a power gain than this.

You have understood our replies perfectly!

 

[Quinn]

Thank you Waynne, and James. You guys Rock 8)

 

[thexav]

I nearly went for Underdrive pulleys! You saved me from wasting my money - again!

 

[the_names_james]

You can buy a lightweight pully set, there's no difference in size so it won't underdrive. Or you could get the standard ones lightened.

 

[obi_waynne]

JAmes - don't you sleep?

 

[the_names_james]

Rarely

 

[Sid447]

Under-drive pulleys,

Are often used by drag race enthusiasts.
The consequence with them though is that a different accessories drive belt must be used as as has been said, they slow down both the water pump, alternator and power steering pump (if all on the same drive).
For weekend or short journey use this might be considered acceptable. But for continual daily-driven/highway use the consequence of the water pump and alternator not turning at the factory recommended speeds should be borne in mind.