Check this radius rod out.
Looks like even guys with cog belt drives need them

this is a mustang with cog belt..




i seen all kind of belt slip and boost issues with supercharger.. the worst idea to get the belt very very tight then it's will extend more and more.
i'm just satisfied with TimRod radius rod. i do not even tight the belt too much like before.

all plates flex so you need to keep it straight with radius rod..

 

That's a good pic.