Proud Member of the 1K Club
Join Date: May 2009
Re: How much hp for a tow behind mower?
I'd say you'll be a bit short of horsepower for cutting tall (field) grass at speed. An 8hp Gravely walk behind (all gear drive, minimal loss) can easily bog out on high grass with a 40" deck in high gear. In low gear with a 30" deck, they are pretty good. Remember that small mowers are typically used for mowing LAWNS, not high grass. Deck throughput clearing the grass end up sucking up a good bit of horsepower. I think that what you are proposing would probably work OK for lawn mowing, but will bog down in high grass.
Mechanical Engineer, Book Collector, and Tractor Nut
1979 Gravely 5265 Commercial
1990 Gravely 16G Professional
1973 Sears SS16 Twin