On my 1971 302 it has a single groove pulley set up. the crank pulley is 6 3/4" diameter and the water pump pulley is 7" diameter. I want to put a double groove crank pulley on. My question is should the double groove crank pulley be the same diameter or do I need to buy a set of pulleys (crank and water pump)? I have an 8" double groove pulley but it won't fit because it hits the water pump pulley, so if I switch to a smaller water pump pulley I will be speeding up the water pump speed considerably.
If you are comparing stock pulleys, the multi-groove crank pulley uses a different (smaller) WP pulley. Yes, it does speed up the WP and probably has increased parasitic losses because of that. Probably speeds up the WP because multi-grooves were used on cars with alot of accessories like A/C and such. My guess is they engineered it that way because the accessories would make the engine run hotter.
