I know someone is gonna come in and tell me im wrong but the basic idea is that overdrive will spin up the acessory and the underdrive will slow it down
Yup, underdrive pulleys will slow down your accessories to free up a few horses. Overdrive pulleys will speed up your accessories, which is helpful to those with blowers. Spinning the blower faster makes more boost and allows for a more reasonable sized pulley on the blower to reduce the chance of belt slip.
So, to combine what the two people above said into an idea that might help you:
With an overdrive crank pulley and underdrive accessory pulleys, you can spin the blower faster while keeping your accessories spinning roughly the same speed they did before.