Revisiting the underdrive pully topic for fresh info.

[Johnny Danger]

Originally Posted by Pat

FWIW, the percentage figures I listed are reduction in drive, not weight. While weight reduction is nice, it is far less significant to me than drive reduction.

My mistake, I thought the percentages that you were referring to had to do with weight . In any case, I found the following info based on a 996 application:

Weight;
Stock - 860.1 grams
BBI - 200.5 grams

Crank snout engagement depth;
Stock - 7.5mm
BBI - 14mm

Overall Diameter;
Stock - 142mm
BBI - 115mm

HP Gains;
8-12.5 WHP

We are proud to say that this is 100% made in the USA...From the materials to the machining and the anodizing.

[Topless]

Don't overthink the pulley. It does improve the life of PS pumps and probably alternators as well on cars that spend a lot of time in high rpm. Remember that the smaller the pulley, the slower the water pump turns so there are practical limits. It does lessen the parasitic loss from running the accessories but dyno results from the Boxster spec series looked like it was in the 3-5hp range. Finding a real 12hp with an UD pulley is the stuff of fantasy. A well balanced pulley is probably far more important than getting the absolute smallest.

[Pat]

Thanks, JD. I'm not confident those numbers also apply to the Boxster pulley. I certainly hope they do, though!
Those figures show a 19% reduction in drive, and a bigger HP bump than I've seen claimed elsewhere. The dynos I've seen with the Boxster UDPs seem to be up 6 to 7 CHP.
Your thoughts? It would be great if this also applies to the Boxster.

[Pat]

Thanks, Topless. The BBI pulley looks very well balanced in their testing. I get the impression like you think the UDPs are all pretty much the same. Also, I am of course concerned the with practical limits you speak of. That said, I don't get the impression I would bump into any of these limits with the offerings currently available. That's why I am trying to split hairs here.
Do you know which pulley the BSX cars are using, and what the drive reduction is?
TIA

[Topless]

Both BSR/BSX classes allow any underdrive pulley with a minimum diameter of 4". I am guessing that someone, somewhere calculated the change in belt speed and determined it was a good compromise between slowing the accessories while preserving coolant velocity. They have been well tested over the last 3 years in a lot of track miles with good results.

[Stroked & Blown]

Do any of the kits come with tools to help with installation? I've seen some rigged-up tools to keep the pulley aligned during removal/installation.

I believe all of the UD pulleys require a boss on the block to be trimmed off, due to the location being inside the stock pulley diameter. If there is an option that doesn't require this to be cut off but still has decent UD, I'd be interested in looking at it - anyone know if this exists?

[AndyA6]

Originally Posted by Stroked & Blown

Do any of the kits come with tools to help with installation? I've seen some rigged-up tools to keep the pulley aligned during removal/installation.

I believe all of the UD pulleys require a boss on the block to be trimmed off, due to the location being inside the stock pulley diameter. If there is an option that doesn't require this to be cut off but still has decent UD, I'd be interested in looking at it - anyone know if this exists?

I have te RSS UDP, it came with the installation tool. My understanding is that the boss has to come off with any of the UDPs. I tried my Dremel but that was slow so I took a saw. One note, get the right wrench to loosen the the bolt, that was the hardest part, lots of elbow grease needed!
Also, I reused the original belt it was in great shape and it works just fine. Eventually I will replace the belt with a slightly shorter one once due.
So far no ill effects whatsoever! There is def some gains, and as mentioned a million times best bang buck mod.

Later,
Andy

[ProjectM96]

Hello. I recently bought an RSS under drive pulley. Kept buying stronger tools with more leverage but I cannot get the old pulley off. Bolt is too tight.

Any help or DIY guides on that?

The RRS UDP came with that tool, but I do not know how to use that tool or why that tool is needed.

What do you guys mean when you say boss or block? And what do you mean when you say it is hard to align the pulley?

I thought all I had to do is remove the bolt holding the old pulley, pull it out, and insert the new pulley+belt.

[Johnny Danger]

Originally Posted by Pat

Thanks, JD. I'm not confident those numbers also apply to the Boxster pulley. I certainly hope they do, though!
Those figures show a 19% reduction in drive, and a bigger HP bump than I've seen claimed elsewhere. The dynos I've seen with the Boxster UDPs seem to be up 6 to 7 CHP.
Your thoughts? It would be great if this also applies to the Boxster.

The 996 stats were the only ones that I could find . I imagine that the figures for the boxster are different . How much is unknown ? However, I would agreed on the 6 to 8 hp gain though .