well got a e mail back from the pulley place i was loooking at here is their reply
"Tony, stock is 3.4" and we offer 3.25" = 1.5lb boost increase, 3.10", 3 lb. boost increase, 3.00" , 4 lb. increase over stock. You will have to change the stock belt, to 1/2" smaller, with any of these sizes. 1 lb. boost is 10 horsepower on these cars. Hope this helps, as also regapping the sparkplugs down .005 setting from stock would be beneficial for optimal performance."
"Tony, stock is 3.4" and we offer 3.25" = 1.5lb boost increase, 3.10", 3 lb. boost increase, 3.00" , 4 lb. increase over stock. You will have to change the stock belt, to 1/2" smaller, with any of these sizes. 1 lb. boost is 10 horsepower on these cars. Hope this helps, as also regapping the sparkplugs down .005 setting from stock would be beneficial for optimal performance."