Increase power of a 9hp engine to 13hp ?

I am putting together a pressure washer to do wet sand blasting, which need 4gpm or more.  I have two 2.5gpm, but one of them kinda not really working,

so i'm building a single bigger one with 4.5gpm.  They say it needs 13hp.  While looking for more two-stroke generators for the v8 project, I thought I was getting another free one with bad alternator, but it turned out it big four-stroke 4k unit, not the little 900w HF jobs.   So I have this free 9hp engine which runs good.

Now I also just bought a 13hp engine in a 6500w generator with no output, and planned to use it, but turns out I can fix this fairly easily, and sell it for twice I paid, so thinking of using the 9hp engine.   Now us gearheads must know how to make almost 50% more power from it right??   The 9hp is 285cc, the 13hp is 390cc, so lot more displacement.

Is there a replacement for displacement?     I actually have two tiny "RHB31/VZ21 turbos I bought for some other hairbrained project I might never get to, so that might be the solution here?

And you are right if you are thinking WTF, just use the $100 engine you dang idiot.  Why you trying to save $100 here?  (well it is saving $250 if I sell the 13hp generator...)

(actually, this is the same generator, someone is asking $850 for it on CL... https://sfbay.craigslist.org/eby/tls/d/hayward-generac-megaforce-6500-generator/7113256378.html

I am wondering if I can just increase the RPMs, from like 3400 to 4000?   Grind the camshaft?  :)   It can't be too hard, although a turbo sounds pretty hard.

Or maybe a leafblower supercharger??   lol

What brand are the engines? You'll get more performance parts on the 390cc if it's a Honda Clone. I'm not familiar with the 285cc but if you can get a 212cc, then there even more goodie parts for it. Using the 212cc, and if its a predator, Get a big valve head and put a hemi head on it, run a four stage header, run the thinner of the head gaskets, run adjustable pushrods, and run a cam on 93 should get you 13hp reliability with a 5500 rpm governer setting.

The 9hp is a Robin/Subaru 265cc (not 285cc).     It must cost less than $100 to get 13hp.   Just found another riding mower with good 12hp engine for $100ish.

The generator motors will prob have a tapered crank that wont work with the pressure washer hookup. The pressure washers i have messed with took a normal straight shaft PTO. 
 

look to a honda clone. You can get 14-18 hp new for under 200$ new.
 

also the motor you have should be safe to run at 4k rpm as is. 

I don't think you'll be able to do anything cheaper or easier than one of these:

https://www.harborfreight.com/engines-generators/gasoline-engines/13-hp-420cc-ohv-horizontal-shaft-gas-engine-epacarb-69736.html

NOS!

Have the cheap honda clones become less cheap? They are all out of china so maybe they got teriff'd and covid'd. 
 

My last one was a "powerland" 420cc or 440cc, it was 179 delivered if i remember right. That was bought prob 2-3 years ago? Sitting on my shelf, never had gas in it. 

Rpm and gear ratio.  If the cam will still make power at 4000 rpm instead of 3000, shrink the drive sprocket 25% and you have 9hp plus 25% more torque.

100 shot

In reply to Ranger50 :

4 shot!

Something to consider with air cooled engines when asking for more power is temperature control/heat mitigation. 
While I like the turbo idea a lot, I think it would be better suited to a go kart or something that sees throttle input instead of a steady 4K rpm. Running boost for more than a few seconds at a time is going to make heat a real issue real fast. 

I'd be tempted to try and raise compression if possible and some port work, maybe a bigger carb. Some of these little engines have cams available.  Back face the valves. That's what I did on my drift trike with a 5hp Briggs and having been on many 5hp karts, I'd guess it was closer to 7... which was fun with no brakes. Pretty easy to spend more hot rodding that to just buy a Chinese clone though. 

My idea is now to go hybrid and use a 5hp electric motor to contribute to spinning the washer pump.   I've got a few motors sitting around.

Or I could just go all-electric, as i have two 7.5hp motors I got from surplus auction for $30 each, they run on 3-phase so few want them, but my shop has 3-phase power.

BTW,  check out public surplus, they are some great deals on stuff nobody else wants.  If it something people want, not super cheap, but can still be cheap..

In reply to nimblemotorsports :

Hybrid pressure washer! This is the answer I didn't know I needed to hear! Make it happen. 

btw, haven't checked into publicsurplus lately, but just did, and there is a 67 Mustang currently at $2,000 in texas, looks rust free!

In reply to nimblemotorsports :

Even better!

TJL (Forum Supporter) said:

The generator motors will prob have a tapered crank that wont work with the pressure washer hookup. The pressure washers i have messed with took a normal straight shaft PTO. 
 

 

look to a honda clone. You can get 14-18 hp new for under 200$ new.
 

also the motor you have should be safe to run at 4k rpm as is. 

Yep, they have tappered shaft, no key.   The low-budgeteer wizard has the solution.. :)

https://www.youtube.com/watch?v=ENcxCRQNBaA

So a hybrid setup is looking pretty interesting, because I realized the 9hp engine has a 4kw generator head attached,

and a generator should also be able to run as a motor!   Should just be able to power it with 120v or 240v AC.

So then I just need to get the pump attached.   Thinking attaching to the flywheel side.   

However, the generator head was not working after after messing with it much too long, I could not get it working, so it won't work as a motor.

Now I do happen to have a lot of Neo Magnets, and could convert it to magnets instead of an induction rotor (Brushless generator), but said oh fck it, a lot of work,

and it will still make a lot of noise, so I'm going with the 3-phase 7.5hp motor.   I tested the motor today, spins up just fine.   

Only problem is its a 4-pole motor so it only spins at 1800 rpm, and not 3600rpm.  So now i need a chain drive to double the pump rpm.

So I've actually done this, haha. We put a turbo on a Yanmar generator a decade ago, so the details are a bit fuzzy. I believe we went from 6hp to around 11hp. The big hurdle with adding a turbo to a low rpm single cylinder is that the exhaust pulse are really far apart, so your efficiency nosedives. With the diesel, it had adjustable timing (mechanical), but it would ping like no other at low rpm/high load until the boost picked up. It sounded like a ballpeen hammer on sheet metal.