New belt driven pump for Honda gx390?

I want to put a 5.5gpm pump on my engine. The direct drive 4gpm pump I have gave out on me, water was shooting out where it mounts to the engine? So what pump could I put on there? Would it be able to handle 5.5 gpm?

The 5.5 gpm, 2500 psi pressure pro uses the GX 390.

Find out what pump that is. How’s business?

Bet it’s a GP T47 series and I have no idea how they claim 2500 psi off a GX390…I calculated it both ways and it falls short of 2500. Maybe 2200…Just not enough HP to generate that pressure at that stated flow.

A gear drive would be a simpler conversion. It’s a straight bolt-on swap.



True but the fact remains that the HP is too low for 5.5g/2500psi

Wrote this in another thread recently, fits here also:

These are the two commonly used equations that most people use to figure up PSI.

(GPM x PSI) / 1100 = HP

(GPM x PSI) / 1450 x 1.5 = HP

According to Russ, he prefers the second, giving the reason that the first pushes the engine to the limit constantly.

A GX390 is about 13 HP, and if you use 5.5 for GPM to solve for PSI, you get:

5.5 x PSI / 1450 x 1.5 = 13

PSI = 2285

The first equation, results in 2600.

And yeah, John, a gear driven will bolt right on easily. Just did it with my GX390.

Now what did he mean by ‘pushes engine to limit constantly’? I’m not 100% sure, but im assuming he meant that if you use the tips to get 2600 PSI, the engine would be cranked hard the entire time. So instead, use the tips that make 2300’ish, so the engine isnt maxxed out. I use the ones that get 2500, which most people use.

Again, just a guess about what he meant.

That’s a good point. How many of us are maxing out the pressure on a daily basis? I can’t remember the last time I had my 7.0 tips in the gun. I think it was when I reset my unloader after swapping it to the other side of the pump, shortly after I bought the machine.

If I was using a surface cleaner for hours on end every day, I might be concerned with straining the motor. But I still don’t even own a SC. And when/if I do, It will be for occasional use and I’ll appreciate having the unloader set at 2500 instead of 2300.

At any rate, this probably isn’t the right machine if you anticipate doing a ton of flatwork, especially on commercial concrete. It’s a housewashing workhorse, though. And having the unloader and tips matched to put out the max pressure will allow you to tackle the occasional residential concrete you get asked to do.

And FWIW, my pressure gauge does hit 2500 psi at the pump, pushing 5.6 gpm. I have no idea (and no real concern over) what I’m getting at the gun after 200’ of hose, though.

My 5.5 gear drive does great (and even 2000 psi is plenty).Please don’t forget, you are SUPPOSED to run small engines wide open all the time. Not doing so is bad for them. Poor maintenance would be a much larger concern, so stay on top of it.

1 Like

Bingo. Especially if you’re not forcing stuff off. Forcing stuff off = damage.

Yes, that is true. I guess the school of thought is that it’s easier on the engine to not run it at 100% LOAD.

A 13HP engine driving a pump that requires 13HP to run has a 100% load. But a 16HP pushing that same pump is only running at about 80% load, even though it’s still at max RPM.

My personal theory is that these small motors, especially Hondas, don’t really mind running at 100% load. And besides, if you’re down-streaming/softwashing with it, the only time the motor experiences a full load is during the split second it takes for the unloader to kick into bypass.

Yeah I’m trying to figure out what pump they use. Buisness is at a stand still right now since my power washer is down. Pretty sure I’m taking this first year as a HUGE learning experience. There is so many things I want to do different for next year. I really learned what matters vs things I want to do.

Are gear driven still good pumps? Everywhere I hear is go with belt drivin. And do you know what pump it is that’s 5.5 2500 psi? I found the eagle series power washer on a website but they didn’t have the pump description (at least I couldn’t find it)

This is what you are looking. Probably find it cheaper elsewhere. I’d try a gear drive now. Years ago they weren’t reliable. Gear and polychain are as good as belt drive now I believe.


Here’s one link for the Udor gear driven pump you’d want. May find a better deal elsewhere.


Bingo. That’s what i was looking for for him

1 Like

Isn’t that way too much psi for the Honda gx390? I was thinking I needed the 2500 psi (5.5gpm) correct me if I’m wrong thanks u

Is gear drive the same as direct drive?


That’s the max PSI of the pump. Using larger tips (7.0) and setting the unloader lower makes it a lower PSI machine.

But yeah, if you tried to use 5.5 tips and kept the unloader at the max pressure, the gx390 would definitely stall.

1 Like