It can knock the rotors out of sync.
@16GoManGoHC2 has some knowledge of this. If he chooses to add to this.
Yea, I read this post, there’s those that believe a solid pulley is ok and there’s ones who believe it isn’t. After disassembling one of these blowers down to a bare case and seeing how their held together and rotors are timed to each other and what holds that Zin place I’m on the side that a solid isn’t good. And the Higher the ratio between drive and driven pulley the worse this becomes as the speed change over time is even quicker inducing more stress. But if you want to spin the blower as fast as a 2.50 on a stock lower will go your better off putting a 10% OD on the bottom and something bigger then a 2.50 on the top like a 2.72 Litens as the smaller you go in pulley size the less circumferential contact patch the belt has for grip. This is just the opposite that is wanted as the faster you spin it the more HP it takes to do such so the need for more grip is needed, bigger pulleys give you such. That’s my plan when I go E85, 10% OD on lower and 2.72 Hellraiser up top but that will be on a blower I’m rebuilding now with super high speed bearings on each end of the rotors and the idler lobe pinned to its shaft once timing is set.
I’m sure you have heard the phrase Pin it before you spin it mentioned about the harmonic damper because it’s not keyed to the crank snout? Well the rotor lobes are not keyed to their shafts either, they depend on clamp load from a bolt to keep them from spinning on their shafts as well. Everything in the blower is like this from the pulleys to the Coupling hubs to the rotors, all are mounted and smooth round shafts, minus the fancy diamond encrusted washer used on the crank pulley. Do you feel lucky??