I had just over 20K on a stock belt with a 15% and it was stretched out about 1" longer than a new stock belt.

Therefore, I would suggest using a shorter belt. Like others have said, if the JCW pulley has a shorter belt, then it makes that a 15% should also run a shorter belt.

I used Gatorback part 060537 (1365mm vs stock 1388 vs jcw 1374)

 

Same here. I think my stock belt may have been slipping a little as well.
The 060537 Gatorback belt works real well with no slipping.

 

We have used exclusively the Gates belts in all our 15% and 17% pulley installations.

The part number for this belt is: Gates K060535

It is a little shorther then stock. Quiet and never had any issue.

We recommend to anyone to change their drive belts every 30K.

Hope this helps

 

Is that part number the same for both a 15% & a 17% pulley?

Thanks,

 

Yes it is,

for 15% and 17% pulley= Gates K060539

and for 19%= Gates K060535

These are the size belts to use with Stock crank pulleys.

 

Thank you!!!

 

That is THE belt NAPA sells. I was looking on the little cardboard sleeve that comes with the belt and it actually says manufactured by Gates.

So if people are looking for that particular belt all they need to do is hit up a local NAPA shop.

 

Or look here:

http://www.napaonline.com/MasterPage...t+-+Serpentine

 

I just completed installing an Alta 1.0 15% pulley on a 2004 MCS...Alta sent me a NAPA 060547 (supposedly same as stock). After the install everything was fine (no squeal or any other issues) until I pushed it hard over 4500 rpm's, then I was getting a lot of squeal. I drove it for a few miles hoping it would "break-in" but it didn't stop. I then read all the posts telling me that the pulley was probably misaligned, but I wanted to exhaust all other options before doing the whole job again to torque the bolts...

In the Alta install instructions is has the following (in table form, with a lot more data):
stock SC + no other changes: NAPA 060547
15% SC pulley (also 17%) + no other updates: NAPA 060539

So I looked at the belt tensioner and saw that it was maxed out (no holes showing and down to the tee) with the 060547 belt installed. So I went to NAPA and got the 060539, installed it thru the right fender in an hour and...problem fixed! No more squeal...thru redline....and wahoo, this is nice!

 

I'm glad you've got that worked out. I used my stock belt when I did the pulley & everything was fine. At 37,000 I put another stock belt on. Still no problems.

 

Alot of people I know are install the NAPA 060535. It is a little shorter than the 539 and allows for a full hole on the tensioner to show. With the 539 I had no hole showing on the tensioner.

 

I got the Napa 535 2 weeks before my RMW tune. I was surprised it only showed 80% of the hole with my 15% Alta. Even Jan asked me about that when he thought I might have belt slip. Compared to the stock belt, the stock looks sturdier & thicker than Napa. I will try Gates next time.

 

Every who is "running the stock belt with 15% with no issues" merely doesn't know that they are having issues. Even my 17,000 mile stock belt was slipping with the Alta V2 pulley. I had no symptoms and thought it was great - woohoo pulley! Then I replaced the belt with the 060539 belt and it was like doing the pulley all over again - I didn't know the pulley was slipping. Another forum member here gained 30 dyno-proven-hp by changing belts because his stock belt was slipping and he didn't know it.

The 060539 belt works pretty good and will stretch to just about the right length. The 060535 belt is a tight fit but provides the most belt tension (which is crucial for power transmission via non-cogged belts).

 

Good to know about slippage issues with the stock belt. All this time I've been blissfully ignorant. I can see that the only way you'd detect slippage is on a dyno. Oh well goodbye bliss hello new belt.

Thanks for the info...

 

You won't regret it.

 

That's not entirely true.

The supercharger belt slipping manifests itself as a boost spike. If you had a boost gauge and saw spikes about 15psi it could be a sign that the belt was slipping. Of course a boost spike could also indicate other issues.

 

It should be noted that a "boost spike" due to a slipping belt would only approach the maximum boost level of a non-slipping belt... so compared to a properly functioning car, one would be more concerned with dips in the torque curve. There is no physical way that a slipping belt can spin the supercharger faster than a gripping belt. "Boost Spike" in this case is therefore somewhat misleading and may cause people to expect a higher-than-normal boost situation with a slipping belt, which is impossible.

 

I'm guessing what you mean is a slipping belt will catch & not slip & that is how the boost spike comes about. Sort of a slip catch, slip catch thing.