help me improve a 31cc engine.

Ok. So I bought a brand new pocketbike. It's a blast. Naturally, I won't stop improving it until I end up hurt.

The new pocketbikes are not two stroke anymore. They are a 31cc Honda gx31 replica from huasheng. It's a whopping 1.2kw! Revs out to like 7000rpm. I would like you gearheads opinion of the little trade secrets for making more power.

So far I have indexed the plug and gapped (might remove the index washer though. As I feel this reduces the already paltry 7.5:1 CR...) I have removed the stock air filter and have just a foam after market one. The stock "can" muffler has been drilled out for better flow. And valves have been adjusted. (FYI- it's OHV.) there is no aftermarket cam for these. But the cam is made of plastic... I've thought about reshaping it for more lift and duration. Is there a way to improve lift on a simple OHV motor without a cam redesign?

There isn't really a way to measure squish, increase compression or bore it out. The combustion chamber and cylinder and ports are all cast as one piece. I've thought about maybe removing the rotating assembly and trying to weld in some material to the roof of the combustion chamber to increase compression. I still have to clean up the ports, but can't hog them out for velocity's sake. I'm waiting to drill out my jet until I finish wothbairflow improvements. No forced induction in this tiny engine world. (Also- no budget for that)

What's the smallest nitrous jet you can buy??? Lol.

And here's some info. My other nerd hobby

Combustion chamber design.

a bit of clay might allow you to get a squish, and a chamber volume. The only visual I get from the pics is the exhaust guide seems to fill the exhaust port. As to adding compression a new piston???

Coldest plug you can find and a jug of nitromethane from the nearest hobby shop?

In reply to BrokenYugo:

My head went there too, but I doubt it would like that much..... The hobby store stuff is for two strokes, lots and lots of caster oil in it.

They have 4 stroke fuel though. Lots of rc copter and boats use four smoke instead of two smokes

I gotta be honest here- if it shoots a rod, great. Then I have an excuse to wedge a pw80 motor in it. So I'm open to "experimental" stuff. How can I increase cam lift and still keep the valves closed?

Reduce the base circle of the cam, I think. There's a limit there before the valvetrain geometry gets too screwed up. Though given that this is an air cooled 7.5:1 SCR engine already making 51.6hp/L there might not be much hiding there to begin with.

What about skimming the head for more compression? It would increase some cam lift, but you might have to do an equal skim of the low side of the cam to close the valves.

Of course I am probably way off in my assunptions...

Old smog pump as a supercharger?

In reply to RossD:

There is no head. It's all one assembly. I know...wtf.

In reply to aircooled:

Interested in this... could it actually produce pressure???

Another thought is to cut the section off that is above the piston, mill it down some, and then weld it back to the jug. But that is getting into some real crazy math Mattix stuff and I'm not prep for that

What about juat putting in a 49cc engine from a scooter? Or even making an electric pocket bike? Neither idea answers your question though.

Add aluminum disc to top of piston?

I'm thinking this is one of those times those leaf blower superchargers you see advertised might actually work

Megasquirt it?

RossD wrote: Megasquirt it?

That's been done! It was microsquirt, but it's been done. That wouldnt add anything to VE though. A 49cc swap works out too, but I would need to purchase that. And it's about 150$, for about 1hp more. Bleh.

carguy123 wrote: I'm thinking this is one of those times those leaf blower superchargers you see advertised might actually work

Best part about that is I could WEAR the backpack whilst boosting!

Patrick wrote: Add aluminum disc to top of piston?

Is that a thing??? Could I seriously, and reasonably accomplish this?

I've heard of the smog pump supercharger being done on successfully stuff like Honda GX160s, Briggs 5hp flathead, etc., you'd probably actually need to underdrive the crap out of one and/or get one from a small 4 cylinder car to have something usable on a GX31. You'll need one with a easily isolated inlet, some draw the air in from behind the pulley and can't be used.

EDIT: Another idea, you'd probably have to get some tiny drill bits to make your own jets, but nitrous is always an option. It would probably be fine with something like a 2 shot (wet), maybe even a 3 shot.

Lolololol. I might need to install a Kevlar tranny blanket between my legs! This could get exciting... I'm immediately searching the smogcharger idea. A nitrous shot sounds spendy though, since I don't have a spare nitrous set laying around. Also, where would I store the bottle? My back? My ass? Lol. There is no suspension on this thing, so i could put a sneaky Pete bottle under the tail fairing?

Trackmouse wrote: Lolololol. I might need to install a Kevlar tranny blanket between my legs! This could get exciting... I'm immediately searching the smogcharger idea. A nitrous shot sounds spendy though, since I don't have a spare nitrous set laying around. Also, where would I store the bottle? My back? My ass? Lol. There is no suspension on this thing, so i could put a sneaky Pete bottle under the tail fairing?

Spent whipped cream cans for a 5 second burst of nitrous aimed into the air filter

No E36 M3 I recommended this to a kid on a forum about 15 years ago for his car and he thought it was serious. In this case though I'm wondering on such a tiny engine could it work. You should try.

There's a dude on YouTube who attaches wood discs to the top of pistons with machine screws to see how long it takes for the wood to burn through. I gather if there is room to the valves one could do that with a disc of aluminum that's thin enough to bump the compression but not interfere with valves.

Can you adjust timing and run E85?

If that guy built a cylinder head from JB Weld, surely you could use it to build up a little dome on the piston. You need some clay like someone said above to figure out your cylinder volume, but if you prep the piston surface well the JB Weld should stick...for a little while at least.