* Engine design: Different engine designs (OHV vs. flathead, etc.) will have varying levels of efficiency and thus output for the same cubic centimeters (cc).
* Manufacturer's rating: Craftsman often uses a "rated horsepower," which isn't necessarily the same as the engine's actual horsepower under load. They may use the advertised "gross horsepower" (measured under ideal, non-operating conditions), which is higher than the "net horsepower" (a more realistic measure of power delivered to the snowblower).
* Engine condition: An engine's horsepower will decrease over time due to wear and tear.
While a 277cc engine might *advertise* in the range of 8-10 horsepower, the *actual* horsepower delivered to the auger and wheels under typical snowblowing conditions will likely be significantly lower, perhaps only 5-7 horsepower or even less.
To get a more precise estimate, you'd need to consult the specific engine model number on your snowblower's engine and look up the manufacturer's specifications. Even then, keep in mind that the stated horsepower might be an idealized rating.
