What horsepower does my 160 cc lawn mower have?

Answer 1

20 hp

Answer 2

There is no correlation between C.C's and horsepower. For example, a 125 CC motor cross bike engine puts out about 28 horse power yet your Briggs 160 CC engine is likely 4.5 horse power. However, you can convert volume to torque and then convert torque to horse power. Actually, a flat head carburetor engine, as a general estimate, is 1 lb. ft of torque per 25 CC's. So your 160 cc Briggs should be about 6.5 lb ft of torque. If you use the formula; torque x rpms/5252 or 6.5 x 2800/5252 =3.5 HP @ 2800 RPM's. Since peak torque rpm vary, lets say it delivers 6 lb ft @ 3600 rpms that puts it at about 4.8 HP@3600 rpm's. Since the small engine manufacturers have no idea what type of equipment there engine s going to be used in, allowances of 20% are considered acceptable. The manufacturers test for torque ( a dyno records torque (twisting force) and calculates horse power from the torque) on a dynomometer with no muffler, air cleaner, cooling fan or any accessories on the engine, if they rate it for x horsepower, that number is derived from an engine tested at peak horsepower with no parasitic loads nor restrictions to the air flow into and out of the combustion chamber. However, lets just say that Toro purchases some 160CC quantum engines which Briggs has rated for 4.5 hp. Toro then installs an exhaust, cooling fan, cooling shrouds, an air filter and then set the engine speed for 3,200 RPM's so not to exceed the maximum mower blade tip speed, horsepower will be substantially less than what the dyno test bore out without the parasitic loads and at the higher engine RPM's. Toro, rather than testing the engine as installed which would be around 3 hp, they label them with the peak torque number because the engine produces it's maximum torque at about 3,000 RPM's. This is used as a marketing ploy since 6.75 torque sounds more powerful than 3.5 horsepower does.

If Toro where to use the engine on a snow blower, which has a much less restrictive exhaust, no air filter and a low flow cooling fan they would likely rate it at 5.5 hp. verses the torque rating. Why; the torque drops off significantly above 3,200 rpm's so the horsepower number is the larger of the two.

An example that shows an under rated engines are the old cast iron Kohler K-series engines. The K-301 (480 cc) is rated at 12 hp and yet it has 27 lb ft of torque at 2800 rpms which equals 12 hp, at 3600 rpms they put out in access of 14 hp. The K-482 is rated for 18 hp and yet it has 37 lb ft of torque! That puts it at around 22 hp at 3600 rpms.

So...your 160 cc Briggs flathead engine is likely 3.5 HP actual as installed on your equipment unless it is a snow blower.