Which under drive pulley to buy/use?
 

Which under drive pulley to buy/use?

Have a Boxster S -- starting to warm up here in Texas -- I track it 2-3 times a month when I can. 90% track car.

Want to save the PS pump.

thanks,

Mike

RSS is not the lightest because it does not have all the lightening hole but it shouldn't break like those do. Running one now on the third season. Saw two of the ones with large lightening hole break out in the spokes. One was posted some where on here one at a DE.

I installed the RSS after doing a bunch of reading and research on this forum. Seems to be generally accepted as the best, strongest solution. Also get the shorter belt...

I have the smaller one from tarett (ie, not the bbi one). seems to be the smallest available. might be an rss unit, dunno. works great. if it is 90% track car, pull out the ac and get a much shorter belt! reduces engine load and weight.

I'll send you a FREE RSS pulley!! No joke. We use a 4inch pulley in spec now, so I have a 5inch RSS sitting here. Had you posted BEFORE the PCA TWS race weekend before last?? I would have hand delivered to you while I brought out a Austin customer car :)

PM me your address!

and Mike.. if you have driven the white 911 in your pic for a couple of years? The small pulley wont help :( 911 drivers who transition into CaymanS and BoxsterS cannot STOP from sawing at the wheel :( it overheats the PS pump and melts the lines.

You will need a cooler in Texas heat for the PS

Thanks, PM'd you.

Unfortunately for me my family Spring Break trip trumps the PCA TWS race :-(

I do get a hall pass most other times of the year tho!

The White 911 drives on rails -- not too much sawing (I think),
now in my 944 chump car -- call me mr lumberjack :-)

Mike

Just taken delivery of the RSS so hope to get it installed in the next month :-)

They work great! and do not fail like the BBI pulleys!

Here is the link with the broken UDP: http://986forum.com/forums/performance-technical-chat/45527-underdrive-pulley-recommendation.html

I just ordered a Tarret 4" UD pulley with belt and bolt.

You are supposed to replace the bolt after removal apparently.

The Pulleys come in different sizes, the RSS is 5" I think which would have more drag than a 4" because its turning the accessories faster, hence more hp consumed.

Still an improvement over stock in any case.

Listen carefully: The 4inch will not turn the AC compressor fast enough at idle to keep the car cool!! So sitting at stop lights.. NO AC. This can happen also with the 5inch if the AC system is not 100%

I never read that anywhere or perhaps I missed that point.

Fortunately the car is rarely stationary for long, no traffic jams on my local routes, so I guess I'll try it out and see if I can live with that.

Do you know what the original pulley diameter is by chance?

I'd be interested in calculating the rpm difference that the accessories will see.

No issues with water pump speed at idle I hope as that is the more important thing.

I did buy a lower temp Thermostat and a new water pump that I will install while I'm in there as well.

Update

I installed my Tarret 4" under drive pulley and all went well and better than predicted.

Particularly, I am happy to report that a 2001 S with the 4" under drive pulley still allows full operation of the air conditioning at idle! :)

Here is the Proof below:

With the Tarret UDP installed and the engine up to full operating temperature,
Ambient temperature 70 F as shown on the guage, and ~750 rpm at idle for over 5 minutes, airconditioning set at full the temperature of the air leaving the vent is ~38 F.
https://lh3.googleusercontent.com/-2...tarret_UDP.jpg

No disrespect Brad, but your information seems to be incorrect for the 2001 S scenario at least.
What model did you have that experience with?
Maybe we can qualify that statement and limit it to certain models?

Tarret UDP and Original
https://lh4.googleusercontent.com/-v...rret_UDP-2.jpg

[QUOTE=jb92563;393339]

This might be on of the most informative pic's I've ever seen on 986Forum - OAT, Tach, Eng Temp, and A/C air temp all in one! Very clever. Great job! :cheers:

https://lh3.googleusercontent.com/-2...tarret_UDP.jpg

jb92563 no disrespect intended but you're kidding with just 70 degree ambient temp as your " test " correct ? Do a follow up when it's 90 + with lots of humidity sitting in traffic THAT is a test.

I had the same concerns before I installed my UDP, there is a great discussion here: http://986forum.com/forums/general-discussions/37563-underdrive-pulley-questions.html

My experience is that the 4" pulley worked fine in all conditions including using the A/C while sitting on the grid for 20 mins while waiting for my turn to time trial during 105F days at the racetrack.

Your mileage may vary.

The point of my test was to prove the AC pump would work at idle rpms.

It created 30 degree temp difference so thats good enough to feel comfortable for a few minutes at the light.

Thats a lot better than no ac what so ever at idle.

I'll update in Aug for some higher temps if anyone cares to know, although I wont be able to produce humidity in CA.

I've had a 4" pulley on the car for a few month and have been pleased with results so far. The real test will be when it hits 110 degrees in July and then throw in a monsoon for some humidity. I will report back then. So far the worst has been a 88 degree day and the car was parked in the sun for an hour so the interior may have hit 100. It cooled down in no time.

To the guy holding the temp gun directly at the vent and testing the AC at 70 degrees....

This test is a fail for several reasons.

#1. Holding the temp gun right in the stream of the cold AC makes the reading artificially lower.

#2. Its 70 degs, but what was the humidity?

#3. When its really hot at stop lights, I sometimes rev the engine to 1200 rpm to get some better AC.

Please revise your experiment and show us a AC manifold hooked up and before and after pic with the pressures.:dance: