Mine is a 13hp Honda and a 3500 PSI 4 GPM pump works great. I use it for washing dump trucks and equipment so it's well used. Make sure that you get a good flexible non marking hose. It's also nice to have a hose real on the unit. Oh and don't fixate on PSI the GPM is as important as PSI. As far as soap injection make sure soaps are added after the pump and don't run through it they are hard on the pumps.
