This rubber, stretchable belt material can be used for many purposes.

The 4" long strip is ribbed lengthwise and can be separated for the width you need. 

Simply cut the length desired and glue it at the underside of the crank or other pulley.

Enough material for several cars.

One rib makes perfect V-belts for alternator & fan, power steering pump, oil pump, nitrous and more.

Cut a wider section and use it for a serpentine pulley system.

It can also be used for a blower belt, but it is not cogged.
 

One 4" belt per package, by Model Car Garage, 1/25 scale.