Is 6.5hp engine enough to run 2500psi

I have a simpson 2500psi pump being run by a 11hp briggs & stratton engine. The old b&s engine
has had it, and i wanted to know if a 6.5hp engine would be enough to run the pump properly.

We were good until you had to go and insert the word “properly”

No. It won’t.

Sounds like now is the perfect time to upgrade.

I see a lot of pressure washers being sold with 2500psi and engines that are 6.5hp. What would be the big difference if I used a 6.5 hp?

The difference being you would no longer put out 2500psi. It all has to do with how your pump is rated to be driven.

That was not part of your question. You questioned whether a 6.5 hp engine would properly run a pump designed to be run by an 11 hp engine.

No, it will not.

If you would ask if it was possible to generate 2,500 psi with 6.5 hp, the answer is an unequivocal YES. Yes, you can generate 2,500 psi with 6.5 hp. As a matter of fact, I have a 6.5 hp engine powered log-splitter that generates 12,000 psi. But that won’t get anything washed. And neither will a 6.5 hp engine where a 11 hp is designed to go.

Heres how I look at it.
Equation for gas hp: [(gpm×psi)/1450]×1.5= gasHP. So reverse work that and you can run 2500psi at ~2.5gpm on 6.5gasHP…but pump gpm is achieved by rpm and pump psi is achieved by HP/Torque. So, what are the original output specs of your pump? Most likely it is will bog down trying to reach 2500psi while adjusting your unloader.

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If you get that smaller engine, you’re gonna have to get a smaller pump.
One with either less psi, less gpm, or both.
I’d honestly get rid of that small machine and get you something that’ll make you more money.
Maybe get a new 11hp engine for like 300 bucks and keep that one either as a backup, or to have a helper do jobs with you.
You can get 4gpm 4000 psi belt drive or gear drive machines for $1500 - $2200, depending where you shop

I’d save the engine though. Maybe turn it into a semi-trash water pump for reclaim down the road!

I know you were asking about 2500 psi but I thought I’d mention have a 6.5 hp engine running an old worn out 5.5 gpm pump. Its great for house washing, cause I don’t need anything more than the 1000 or so PSI it puts out. Best part is I combined two existing machines I wasn’t using so all it cost me was $7 for a pulley and the time to assemble.