What Modifications Would Improve the Performance of a Honda 5.5HP Kart Engine?

[Fantastic Fox]

I have 10 weeks to complete a project on a Honda 5.5HP 4-stroke engine. The engine is for a kart. It is normally aspirated and has a sponge carb.

I must do the following:
(1) Examine the design/construction of the engine
(2) Propose a new/modified design
(3) Build
(4) Test
(5) Report

This is the engine: http://cgi.ebay.ie/GO-KART-KARTING-5-5HP-ENGINE-ALL-PARTS-FIT-HONDA-GX160_W0QQitemZ270207881196QQihZ017QQcategoryZ122308QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I have a lot of ideas about what could be modified, but I'd like to hear other people's opinions. What do you think would yield the best performance increase? 10 weeks is a very tight timeframe so that also has to be considered.

 

[brewnog]

What does your new/modified design have to accomplish? Just performance? What's your budget? How long does the engine have to live? What other constraints do you have on your modification?

 

[Danger]

What the hell is a 'sponge carb'?

 

[Fantastic Fox]

Improved performance is the goal. There is no set budget, but I'd say less than $500. The engine life isn't very important. If compromising the life of the engine is needed to improve performance then so be it. There are no constraints on what can be done.

Sponge air filter. Sorry.

At the moment, I'm thinking about designing either an air intake, air filter, or exhaust.


Thanks

 

[Danger]

Sponge air filter. Sorry.

I rather suspected that that's what you meant, but I've learned to never assume around here. Someone might have come up with something like a porous ceramic to replace the venturi or some other weirdness like that.

 

[brewnog]

500 dollars (I assume US), with no limit on life, durability, operating range, noise, vibration, etc etc?

For out-and-out peak horsepower for a few hundred quid I'd be looking at a turbo (scrapyard) and nitrous kit (homemade). There's not much point spending money on modifying the core when you can get such big peak power gains from 'easy' bolt-ons. You might want to look at a bit of head porting if the current one is really bad, and a really free-flowing exhaust manifold may help you realize extra power more easily. Obviously you need to find a way to raise the fuelling too, and possibly to provide better ignition control.

I know you probably don't care ("no constraints, just get more power!"), but I would be worried about cooling, balancing, valvetrain life, bottom end durability, control, safety, lubrication and response; and when put in a vehicle I'd be worried about driveability, handling, ride and braking too.

 

[Danger]

Full agreement with Brewski; there are dozens of small-scale things that you can do which, taken together, can add up to some serious hp gains. I'm not familiar with the engine type that you refer to, so some of these might not apply to your case. My experience is with V8's.
If the thing has a crankcase, you can pick up a lot by simply installing a windage tray. That's a thin sheet of steel that bolts in between the block and the oil pan. It separates the pan completely from the bores, except for precise cut-outs for crank journal clearance. The purpose is to scrape oil off of the crank, and prevent it from splashing up onto the rods and pistons. That lowers drag on the rotating assembly. For my Roadrunner, it was worth about 15 hp. A more expensive alternative would be to go with a dry-sump system.
Narrowing your piston ring clearance can help, at the possible expense of longevity. My double-moly rings are supposed to be gapped at .035; I've got them at .008. While it's not recommended, I never had a problem. They were supposed to be good for 10 passes in the 1/4 mile before replacement, but I got over 30,000 miles out of the first set. The narrower gap means less blow-by and therefore more of the combustion pressure applied to the piston.
Throw in an ice-cannister heat exchanger to chill your fuel before carbeurtation, and use a cold-air induction system. Both give you a denser intake charge, and thus more power per stroke.
Don't scrimp on the ignition system; a hotter spark gives a better burn, so go with a high-output MSD or magneto and good plugs.
Go with the lightest valve springs that will handle your rpm range, to cut down on cam drag. In some cases, progressive springs work better than linear ones.
Port and polish the heads, as Brewski mentioned. If you don't feel like machining them (which is very simple with just a Dremel and grinding stone), then paint them and sand the paint after every coat. (Old Smokey Yunick trick from NASCAR.)
Sometimes a bit of back-pressure is a good thing, so you might be farther ahead with a low-resistance muffler than just running open headers. That requires experimentation to determine.
An optical or magnetic distributer gives you some advantage over mechanical points, since they're more precisely timed and don't 'bounce'.
I'm going to pack it up for this post. Will get back to you. I hope that Stingray weighs in if he's still around; the dude really knows his cars.

 

[wolram]

These engines usually have a governor to avoid over revving, that would have to go first
may be then you have an extra 2000 or what ever rpm to play with.

 

[NateTG]

If it's practical, conversion to Nitromethane fuel is likely to give you a bunch of power, as might Water/Methanol injection.