I just replaced my serpentine belt (Gates K081145) on my SRT6. I believe the length of the belt is 114.5 inches when new (ie embedded in the part number). Once installed, I then carefully measured the old belt. Its length was 117 inches. The belt was original and the car has 54,000 miles on it. So, after 15 years and 54k miles, the old belt had stretched by ~2.5 inches. Anecdotally, the before and after driving experience was significantly better - it pushed me back in the seat in a way I hadn't experienced before. Quite significant and definitely unexpected.

Unfortunately (or really, fortunately) I discovered that the harmonic balancer is pining for the fiords. It will be replaced pronto with MB part #

1120351600

That should make my engine much quieter too!

Cheers,
Dave