GX690 with Comet tw8030: GPM is 9.5. Help?

So i have the common, 8gpm, 3500psi combo (that i know isn’t possible at 22HP).

Yet my pressure gauge is showing 3100psi while running 090 (or 2 x 045), and I am consistently getting about 9.5gpm. Which puts me at 26hp… not possible right?

I’m reasonably confident in the GPM number as i’ve tested it with tips, bare, and my bypass is still pushing a steady 1.5 GPM while the hose is running 090 wide open. So i guess that means the pressure gauge is incorrect?

What I am trying to ask, in a very roundabout way: Is there a way to modify the GPM - PSI ratio your machine outputs, or is that completely dictated by the Pump purchased, and not adjustable?

Normally I wouldn’t look a gift horse in the mouth, but I think the higher GPM is affecting my ability to downstream. My 2.3 Injector (rated for 5-8gpm, 4000psi) seems to only be pulling at 30:1, even wide open with no nozzles. It advertises 4:1. Part BE:85.300.095

Can anyone help with any of this?

Do you have a tachometer on your motor? Because it sounds like you’re over-reving it.

GPM is dictated by pump displacement and speed. You can adjust pump speed by swapping pulleys, or idling down your motor.

PSI is a product of a given amount of flow being pushed through a particular sized orifice. Once you’ve got your pump dialed in at the flow you want, either by adjusting engine speed or swapping pulleys, use a nozzle chart to select the right size orifices for your desired psi.

Regarding your issues with the ds injector, your draw rate should improve a little when you bring your pump speed back into spec. But I would still recommend swapping it out for a tried and true GP hidraw, or the stainless proportioning version of it sold by a couple of vendors.

Okay, I’ll put a tach on right now. What is the ideal RPM?

Edit: Google says 3600RPM is ideal, and thats what it’s running at, so occams razor says my pressure gauge is off. But it still seems weird that the machine, running at ideal RPM, is putting out almost 10 GPM.

I’m just glad more than a handful of people here know what that is.


And try a 3-5 gpm injector


The GX 690 has more HP past 3600rpm. The curve is still going up at that mark…unlike my GX630. I wouldn’t doubt it could put out 26hp.