Along the same lines... and I know this is going to sound crazy, but I saw it with my own two eyes. Unfortunately it was a number of years ago and it seems the website has changed since but...
I was surfing the web and stumbled on a page on Briggs & Stratton's website about their 5 HP horizontal-shaft engines. Those engines are (were) used extensively in go-kart racing, and the page was discussing ways to improve the performance of those engines.
So here's the shocker: one thing they discussed was exhaust upgrades - in the sense of better or no muffler, not port work or anything like that. They said that just by removing the (apparently awful) stock muffler and replacing it with a straight pipe, you could get an 80% increase in power! That's not a typo: making that one change would turn your 5HP engine into an 8HP engine. Since engines used in that application are not governed, I suspect the 8HP comes at a higher RPM than the 5HP but I wouldn't consider that a "modification".
Not that I'm recommending straight pipes on snowblowers, but I did find that info pretty surprising.
~1994 Ariens 924084 (ST1032) "papa bear": restored, re-engined, real nice!
1991 Ariens 924050 (ST824) "mama bear"
Toro PowerCurve 1800 "baby bear"
Be alert! America needs more lerts.