boostedfury

Hey guys I am about to do a cam swap and will be using an SLP 25% UDP. The belt numbers from slp directly have been known to be wrong, and I am seriously confused at what belts will work. I do not want to order belts to just have to return them.

So pretty much what sizes should I look for for my 99 c5 ls1 with an 25% UDP and stock size idlers!

dadaroo

The circumference of a pulley is Pi times the diameter, or Pi times 2 times the radius. This measurement should be from the actual base/bottom of the belt pulley grooves. Assuming the belt goes around 180 degrees of the pulley then the "added" belt length of the stock pulley size would be half of that. Calculate the same amount for the undersized pulley and determine what reduced belt length you are creating. Subtract that from the actual stock belt length. If the belt goes around less than 180 degrees of the pulley you can just ratio the smaller partial circumference change instead of 1/2. Hope this helps, if not just PM or email me with your phone number and we can discuss.

PS: You should be able to measure the original belt length or get it from any manufacturers web site. Let us know how it works out for you. I provide a money back guarantee on all my guidance.

boostedfury

That seems way over my pay grade haha any other input is also greatly appreciated!

rodsvet

Take string that isn't "stretchy" and carefully wrap it around the pulleys exactly as the belt would ride. Cut it and measure it. Most belts have the length on the package or in the book at the auto parts store. Just make sure you don't make the belt unreturnable in case you need to go up or down a size. Rod

martysauto

It will be too long, the tensioner will not be loaded. You would need a second person to move the tensioner pulley about half way or more. To get the correct measurement.

dadaroo

OK, I have another idea for you. Look at the old pulley now and see where the belt is touching the pulley (in the grooves). Use a measuring tape or something to measure the length of belt that is in contact with the pulley. That will be what we call length A. Next take your new pulley and replicate what you did above by measuring a similar arc on the new pulley where the belt will be in contact. That will be what we call length B. A-B=C where C is the amount of belt length you no longer need. Get the original belt length and then subtract C from that for what your new belt length should be. Any minor error is measurement should be more than taken up by a tensioner.

PS: I recommend you go with Gatorback belts. Many people have experienced belt squeal with other various brands. Seems like some brands have deeper belt grooves that allow the belt tips to ride/touch the pulley groove bottoms thus making noise.

boostedfury

Thanks for the advice, I cannot fathom it is this hard with so many varying part numbers....the numbers apparently are wrong from SLP, the local store doesn't carry gates, and when I type in a recommended one on amazon says will not fit my vehicle...ugh.

Bump for someone using the slp/power bond 25% UDP for part numbers!

rodsvet

There have to be 100 guys who have done this. Hopefully some one will chime in on the belt number they used. And yes the tensioner must be at 2/3 or more but not tight when measuring the string. I thought that didn't need mentioning. Rod

Evil-Twin

I used a 4PK1015 4PK = 4 rib 1015 mm = 40 inch for the AC belt
I used a 6PK1930 6PK = 6 rib 1930 mm = 76 inch for the drive belt

4PK1015 = 5040400DR
6PK1930 = 5060760DR

Good luck
Bill aka ET

dadaroo

[QUOTE=boostedfury;1585750075]Thanks for the advice, I cannot fathom it is this hard with so many varying part numbers....the numbers apparently are wrong from SLP, the local store doesn't carry gates, and when I type in a recommended one on amazon says will not fit my vehicle...ugh.

And WHY would you expect a nonstandard size belt to show as a correct fit for your car?????????????????????????????????