Drumsonly2002,
Intake and discharge dynamics contribute most to throwing performance (fan diameter, blade geometry, # of blades, discharge geometry, chute profile, impeller speed, auger rate/efficiency, etc.). As long as you have enough horsepower now, the performance won't increase much with additional power. 10hp is surely enough for most units, especially with the torque advantage of 358cc's (Tecumseh LH358SA). I've played with and observed some units with monster engines that didn't have any real benefit.
I would also advise you not to speed up your impeller past the factory setting. This could result in counterproductive recirculation and also possible safety hazards (detached blades). Many snowblowers are put through a test in which a steel stake is inserted into the fan at speed. Nothing can detach from the unit at the maximum operating RPM per the standard. If you speed the fan up, well, its pretty self explanatory... Increasing the engine sheave size will also alter your clutching/belt finger/brake geometry possibly creating a another hazard (the impeller may not stop properly when you declutch).
If you want more distance or capacity, you may want to look at another blower. The 13hp OH358SA will be noticeably smoother and will maintain RPM's better at the EOD, but the power increase may not be what you expect.
One thing to note if you keep the unit, you may want to try a raw edge belt for the blower head. Definitety an Aramid cord belt and keep the tension maintained. It'll chirp when you engage the head. You will get a few extra feet if you're currently using a conventional wrapped clutch-cover belt (especially with a larger displacement engine).
Also, I believe I posted somewhere about the fitup differences between the engines. The crankshaft is .5" higher, and the engine mounts need to be rearset by .220" due to the counterbalancer girth at the PTO cover. Be sure you compensate.
I hope this helps.
PK
