Sbc Water Pump Pulley Info

I need to overdrive my water pump about 400 RPMs at idle. I presently am running a 1:1 ratio with 6-1/2" crank and water pump pulleys. Can somebody tell me where to get a smaller water pump pulley (5/8" shaft, single groove) and how much smaller?

Thanks in advance.

 

first off, WHY??
and secondly, what RPM are youcurrently idling at? can't tell you a percentage of overdrive if I don't know the starting point. if it's 800 rpm you need a 50% over drive, meaning you need a 3.25" water pump pulley. GOOD LUCK with that one

 

Probably one off of an older 6 cylinder.
4.75" would be 1400rpm with a 6 1/2" at 1000 rpm.
of course at 4000 rpm your pump will be singing at 5600, and you may have to use a long pump to clear the smaller pulley? Or perhaps you could use one of the risers that uses a 6 cylinder pump?

 

I'll ask again,,WHY!!!!!!

 

Me 2!!