The pulley diameter is smaller than stock to slow down the water pump at racing RPM. Surprisingly, it didn't cost the earth & is credited with eliminating the "flywheel coming loose" problem that "A" series engines sometimes have.
OK,.. that "this" "A" series engine had.

It is my hope that i can get a more street friendly version of this thing made for my GX engine. I will go with a stock size pulley & a smaller damper ring [although it might be thicker]
Anything for smoothness & reliability.