Use a tape measure to get belt length. Just run the tape measure the same way the belt will be routed for length. It should run everything fine but it will spin everything faster if it is a smaller diamater. It is another way to spin your S/C faster for more boost.
The ratio of any two drive accessories can be determined by dividing the diameter of the smaller pulley into the larger one. For example, if a 6-inch water-pump pulley is used in conjunction with a 7-inch crank pulley, the pulley ratio is 1.16:1. So for every 1,000 rpm the crank pulley spins, the water pump would rotate 1,116 times. Since the water pump spins at a faster rate than the crank, it's said to be overdriven. Flop things around, and the water pump would spin slower than the crank and be underdriven. Underdrive pulley sets are often used to reduce the parasitic drag on the crankshaft to increase horsepower; however, altering the speed of the accessories can have adverse affects on the performance of the related systems, especially if they are already overburdened.I just looked on ATI's website. The only undersize that they sell for this engine is a 5.5" which is a 15% under drive. Being my car will still be a still car what should I do? I do plan to spin the engine pretty hard, but don't want to suffer from not enough water circulation or alt volts when cruising.