If I understand correctly, the OEM belt length can be used if you reduce the supercharger pulley by 15% and get a 2% oversized crank pulley at the same time.

It also sounds like if you only use a 15% sc pulley reduction, you can reuse your stock belt, but it is advisable to use a shorter replacement belt.

If these thoughts are true...why not just output a little more to buy the +2% crank pulley and retain the stock belt? You even get the added benefit of acting like a 17% sc pulley reduction...am I missing something? what are the concerns?

 

The inexpensive over-sized crank pulleys have no dampener on them, and can theoretically cause undue W&T on your engine. And a crank pulley with a dampener is much more than a little more money.

Also the belt drives more than just the SC, it will also change the speed of the alternator, A/c, water pump etc. Which MIGHT contribute to a premature death of any of them.

If you want a 17% pulley, get a 17% pulley. Way sells them for the same price as the 15s

 

A few thoughts....
Don't worry about using the "stock" belt.....
Always use a new belt....and one of the correct length if you do work on the pulleys...the belts are so cheap...and so important!! Old belts break, stretch, and need to replaced....the "stock" belt CAN work with a 15% for a bit...but it WILL SLIP as it ages....so it is a false sense of economy to reuse it.....The folks who sell you the Overdrive pulley will give you a chart or answer your question and tell you which belt is correct!!

The 15% and the +2% combo is the rough equivalent of a 17% reduction....It is an option for some...and a compromise....
An example is if you have a 15%, and you damper goes bad...you can get a fully dampened pulley that is slightly over-sized for less then the OEM, and a more relivable design too....WMW and RMW both sell dampened versions....DO NOT GET AN CHEAP UNDAMPEND PULLEY IMO!! They come dampened for a series of specific frequencies, to protect the crankshaft, it bearings, and even the alternator, SC and AC pump....Harmonic vibrations can cause great damage if they happen....the orgional engineers said there was a chance ON THIS ENGINE...so they spece'd one...and cost the OEM some $$$ to do....so it is safe to say they did a cost benefit calculation.
I said it was a compromise....but it does have a benifit...the belt SHOULD wear more evenly than a 17%...and be less likely to be thrown off at higher rpm's.....BUT the NEGATIVES...
Cost....higher...but if you need a NEW damper, and want a bit extra power...kill 2 birds with one stone....BUT as an astute mechanic will point out...you will be running the Alternator and AC compressor at higher than normal speed....could be a bit more wear, shorter life, or a bit of trivial power loss...folks for years on other cars have been using bigger alternator pulleys to try to reduce the drain of the alternator on the drive-train for some apps (an old street rod/hot-rod trip if you have ,minimal need for power)...the same can be done in this case to prevent the possibility of overcharging....and to slow it down to its design speed....no such mod is around for the AC compressor.

 

all your posts definitely make sense. i'm convinced! i'm avoiding the lightened crank pulley mod.

 

If you end up wanting a larger diameter crank pulley, let us know. We have a 2% oversized damper.

 

thanks way, I actually bought one of your 15% pulleys just the other day. But sounds like the extra stress on the peripheral systems doesn't sound too appealing

 

if you have a older R53 like a 02 isnt even the aftermarket dampened crank pulley lighter by a few pounds? so wouldn't this be a plus as well ?

 

Yes the ATI Damper is lighter.

02-04 crank pulley 7lbs 1 oz

ATI Damper 5lbs 9 oz