The engine on your machine is an MTD engine. They are partnered with a company and are collectively building the engines.
The horsepower question is a loaded one. I will give you, what I feel, is a very good and accurate definition of horsepower.
HORSEPOWER is a measure of work and power created as a marketing ploy by inventor James Watt around 1775 to promote his newfangled steam engine. Textbooks define WORK as force multiplied by distance, and POWER as work divided by time. To cut the physics lesson short, here's the math formula: engine revolutions per minute (rpm) multiplied by torque at that engine speed, divided by the constant of 5252. Or RPM x TORQUE divided by 5252 = HP
Horse power is such a complete variable number that can/is determined by everything from the grade of gas, to air temperature, to humidity, to barometric pressure. There are a host of reasons why small engine manufactures have, and continue to, gotten away from putting a horsepower number on engines. It's just not a reliable way of measuring what an engine will and won't do. For example: I have 2 trucks that both rate 220 horsepower from the manufacturers. One truck will pull a house and the other does good to pull a small trailer with a medium load. This is because the one truck has massive amounts of torque (460 CID big block) and the other doesn't (305 CID small block).
I know that all seems like a great big mass of trying to NOT answer a question. I assure you, it is not. It's just that the horsepower your engine makes today will likely not be the same tomorrow, or even a few hours from now. It's just not a number worth trying to come up with. Realistically, the horsepower could be expected to be somewhere in the area of 5.5 to as much as 9.5, depending on all the variables.
The engine in question has been in production and use for a few years now. I have seen it used on snow throwers, tillers, go-carts, and air compressors. I expect to see it on more and more machines in the future. MTD is also working on getting a bigger version of the same engine on the market soon. The problems I've seen with these little engines have been minimal. For the most part the issues are usually carburetor related. Most carburetors that are made for small engines anymore are very delicate in that they cannot take the beating that carburetors 20 years ago could take. The EPA standards that have to be met have really put a damper on being able to make adjustments and fine tuning like we once could.
I apologize for this turning into such a massive answer. It's just that horsepower is irrelevant as far as what an engine is capable of doing. I hate to see people become twisted up into a number that is forever variable.
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