Motor size

I currently am running a 5.5 gpm machine and its great. However I was thinking about building a 4gpm as a backup. Does anyone know if an 6.5 hp motor will do fine with a 4gpm pump? The reason I’m wanting to use an 6.5 is because I already have it sitting in my shop. Thank you

It’ll work for house-washing. You’ll be limited to around 1,700 psi or so.

How much gpm / psi can you get out of a honda 390 belt drive?@infinity

The formula is kicking around somewhere, but from memory, these are the common configurations:


Thank you sir @Infinity. Much appreciated. I’ve been searching. Just so much miss info.

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PSI times GPM divided by 1100 equals needed horsepower


So a gx390 should be able to handle 5gpm at 3000 psi no problem?

Honda rates a GX390 at 11.7 horsepower. 5gpm at 3000psi requires 13.64 horsepower, if you divide by 1100.

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I’ve seen it advertised as 13 hp but good point.

Of course 4gpm at 4000 psi would require 14.5. :astonished: