Larger pulleys have less slip and greater belt life
--A snowball effect in the correct direction!! (no pun intended)
Best situation is to match pulley's to equipment.
Throttling down decreases H.P. available to do work.
Now that said, small differences in diameters usually is not noticable,
but one could try changing the driven pulley a bit and try it under actual use conditions
Ideally, an engine would be at full governed rpm's, while the thrower would have a full mouth of snow, going at a comfortable foward speed.
but so many variables are to be considered, so the engineers try to achieve a happy medium.
Pulleys are relatively inexpensive at surplus places/ 'net etc.
of course a belt length change will have to be considered is some cases.
A higher speed auger is ideal in light fluffy snow, but drags the engine down in sloppy wet chit.
I went to one more tooth on the jack shaft to increase RPM of the auger/paddles as I have a stout M-18 to power it.
I only mention that as there are more than one way to achieve
Rpm changes.
You could go 1 tooth less to decrease final auger rpm.
You would have to do the math to see what your final rpm's are.
One might hang a Qa on a say 14 or 16 hp GT, and find in heavy stuff it is slow going and/or you will run out of HP and clog your chute.
Just something to think of on a sleepless night.
If I were doing your installation, I would match the gearbox pulley to that of the drive PTO of the engine.
I changed the sprocket, only because it was badly worn and I thought if I was going to change it, why not see if a bit more Rpm's would be helpful.
