I thought the honda gx390 is 13hp

[The motor guy]

Does the vertical shaft model have less hp than the horizontal shaft?

 

[The motor guy]

Yeah so the horizontal shaft gx version is 13hp and the gxv vertical shaft is only 10.2hp, what's up with the hp difference?

 

[The_Jeff]

That could be the HP at a governed 3100 RPM to meet the consumer product safety commission max blade speed.

 

[The motor guy]

That could be the HP at a governed 3100 RPM to meet the consumer product safety commission max blade speed.

That explains it, but then again commercial mowers run at 3600rpm all day long. That's a residential thing I believe

 

[Cujet]

The Honda GX390 has a bit of an odd rating system. As a general rule, an overhead valve 340cc, 3600RPM engine is equal to 11HP, or about 31cc per HP. (more modern flathead engines are generally about 33cc per HP)

I've seen GX390's with ratings from 11 to 13HP, all at 3600RPM. My guess, there is no real world difference in output.

 

[The motor guy]

I did notice the hydro gear transmission requires no more than 3100rpm on the mower I bought