The JR Race Car 3/4" wide belt is designed for use on the Shockwave clutch.  Lower chugs on the belt allow it to be flexible and strong. 
 
Several centers are available for the 3/4" line of belts.
 
SKU                        CENTRE DISTANCE***
545-34579                            6 1/8"
545-34580                            6 7/8"
545-34581                             7 3/8"
545-34582                             8"
545-34583                             8 3/8"
545-34584.                            9"
545-34585                             9 1/4"
 
*** Centers: Is the distance from the center of the crank shaft to the center of the jackshaft. (Measurements are approximated)