Gerry Hayne

I also have an older Airco Model ACF-130, and cannot get the standard filters, so instead buy a larger filter at Home Depot and cut it down, fiberglass easy to cut, and replace the cardboard end caps with a bit of tape to hold in place. The fiberglass is not terribly effective anyway. I am in process of replacing the blower motor, and new motor is 1/3 hp, versus 1/4 hp of original motor. My question is whether I should change the size of the motor pulley or not? The furnace has an information sheet on the front, saying the furnace pulley ratio is: 3.25 x 7 for 1/4 hp, and 3.25 x 5 for 1/3 hp. The fan pulley is 7". What does the "pulley ratio" calculation suggest(?), to those familiar with their terms?