fmmoto

Do the lightweight pulley's make a noticeable difference? I'm not looking for measurable power increases but a seat of the pants difference would interest me.

FLY996

I'm running the RSS underdrive pulley (I bypassed A/C as well). Definitely gives a noticeable seat of the pants boost in acceleration.

Ck986

I didn't feel the upgraded pulley in the boxster. Appeared to be a waste of money.

5CHN3LL

I have run underdrive pulleys on both of my M96-powered cars. It's the best "bolt-on" mod you can buy, in my opinion. It was one of the last mods I tried on my Boxster, after burning a good deal of money, and I ordered another one the same day I took possession of my 996.

The only downside I have noticed is that underdriving the alternator can leave the car with a less than optimal charge. This is only evident when I leave the car parked for days between trips...which isn't often. This is a minor issue of the voltmeter reading .5-1 volt low after starting, again after sitting for several days. Frequent driving and/or my battery maintainer addresses this issue.

As someone else will eventually point out, the u/d pulley doesn't increase power, but it does cause less HP to be used driving the belt-driven accessories which can prevent some accessory issues when driving @ higher RPM for extended periods (i.e. track).

There are several designs. I'd recommend using a solid pulley or one with minimal material removed rather than the skeletonized versions that remove most of the material. See p. 2 of this thread for pics:
https://rennlist.com/forums/996-foru...-pulley-2.html

5CHN3LL

One other note: Installing an underdrive pulley on the 996 is SO easy compared to the Boxster. We're talking about minutes on the 996 vs. hours on the 986.

5CHN3LL

It's the diameter of the pulley, not the weight, that's important in this case.

996pp

I have also been debating on getting the U/D pulley. The main reason I have been wanting to get it is because when I turn on the A/C I can really fell the power loss from take off at stand still. I have been meaning to ask you 5CHN3LL if you can feel a difference on your car with the U/D on there.

5CHN3LL

It's not a tremendous difference. I believe the U/D pulley reduces the parasitic draw of the belt-driven accessories by 20%. It's absolutely noticeable, but not the same kind of noticeable as adding a hundred-shot of nitrous. It's a small but noticeable gain, which is all you can ask from for a mod in this price range. I feel that it revs a bit more freely.

I'm happy I did it. Twice.

996pp

Any downsides to doing the mod?

5CHN3LL

The only downside is the one I mentioned earlier - my battery can wind up half volt or so low if I have only done short trips and/or let the car sit. If I'm not lazy and use the maintainer if the car's going to sit, I have no problems.

I've had the pulley installed on my 996 for about two years now.

kdm

I ordered the RSS pulley from GSR Autosport. They were back ordered so don't have it yet but will be installing it within the next few weeks. I'll post back after I have a few miles with it. Not expecting any great improvement, just subtle bump in responsiveness.

pmkazz

Just out of curiosity, how come you didn't order it directly from RSS?

txhokie4life

Another downside is my Boxster runs hotter if ac is off.

I think the rpms are too low to drive the water pump

If you keep the ac on, rpms are up ~150 and temp lowers

Mike

mcipseric

It think the theory behind the under drive pulley is to reduce the speed of spinning parts attached to the belt. Since track cars live mostly above 5k rpm. Street cars do not.

kdm

No real reason - Internet search had them high on the list, web site was easy to navigate and price was the same. After I placed the order they told me that RSS was backlogged on production so they would be out of stock for 2-3 weeks. Might not have been the case if I had gone direct but I'm not in any great rush so was willing to wait.