Hot Rods tach drive ratio adapter question

I plan to use a late 50s Corvette tach drive generator and SW 5000 tach... the generator pulley is 3" diameter and the crank pulley is 6 1/2" diameter (324 Olds)... what ratio adapter will I need?... Thanks for the help...

 

get it put together without an adapter, and see how far off it is, and go from there?

 

Talk to rusty

 

Try this, https://www.blocklayer.com/pulley-belteng

 

If you don’t have a way to check the RPMs a different way (wire up an electric tach temporarily), you will need to find the diameter of the original Vette crank pulley. Then you could find the difference in cir***ference between the old and the current pulleys. That would be needed to see what percentage you are off.