Has anyone had any problems running a crank underdrive pulley? I bought the one from Rotary Performance about a year ago before my engine died. After getting a new engine 4 months ago, I was insterested in putting this thing on, but I have heard that it is big problems for street cars since the altenator doesn't turn as fast.

How about running this in comination with the dual belt altenator pulley?

 

The dual alt belt pulley is for higher RPM running, it helps stop the belts from slipping on the water pump and alternator.

What you need to do is swap the water pump pulley with the air pump pulley and you will be fine...

 

Well, that is not exactly what I was asking. Currently, the air pump is on my car and I am running all the stock pulleys. As soon as I determine what I need to do so my 6 port actuators will continue to work (S4 6PI doesn't run off of air pump?), I am going to remove my air pump and put on the dual-belt altenator pulley.

What I want to know is if I put the under-drive crank pulley on, will my altenator be able to keep my battery charged driving around town?

 

The battery should be fine, id be more worried about it slowing down the water pump and increasing coolant temps. The gain isnt worth putting one on IMHO.

 

Even for an NA? They don't burn as hot, I thought.

 

N/As run very hot..

Your wasting your money on the dual pulley, those are for race cars, that run higher rpms for longer periods of time. You will get no benefit from adding this..unless you don't tighten your belt enough....

The part about swap the Air pulley for the water pump pulley is for the underdrive pulley. You will need a larger pulley that rotates slower, or you will have made your car worse and it will overheat...because the stock pulley is only good for up to 4000 rpm after that they just foam up the water....Hence why everyones car heats up after driving it in the upper RPM range...

 

ok, gotcha.

 

But not nearly as hot as turbos.

If the airpump is removed, then the dual belt pully is a MUST when using the stock clutch fan. If the stock clutch fan is NOT used, then then dual belt pully is not really necessary, but still recommended.

Actually, it's around 5500RPM or so where the pump starts to cavitate.

 

Is there any way to clutch the water pump so that it won't cavitate above 5500? or would that just add a ton of weight?

 

Aaron, that's the way I understood it, both about not running the air pump and the running temp.

So it sounds like running the crank pulley isn't a good idea. Thanks for the help guys.

 

Get a set of pullies.

 

You're confusing two seperate issues.
The dual-belt pulley is required when the air pump is removed. Because there's now only one belt running the water pump (with a small contact patch), the water pump tends to slip on acceleration, particularly if the stock fan's thermoclutch is engaged. A dual-belt alternator pulley allows a second belt to turn the water pump, to stop the slipping.
An underdrive accessory pulley simply runs whatever it's attached to at a slower speed. An underdrive main pulley will run everything slower. Spinning the water pump slower will avoid cavitation at high rpm, but actually reduces cooling capacity. That's why they're recommended for use on race cars, not street cars. Underdriving the alternator is not recommended, as the FC's alternator isn't that great.