increase power/torque of a 2 stroke

[hks_kansei]

well, i am going to build a go-kart in the near future using a two stroke engine from a lawnmower, and relocating the fuel tank and carby to allow a horisontal driveshaft.

my question is, what can i do to increase the power or torque from the two stroke, i read about something along the lines of a resonating exhaust that creates backpressure to force the unburnt mixture back into the combustion chamber, and therefore creates more power, but this sounds very difficult to get right (assuming it works, unlike electric superchargers)

would simple things like better flowing exhaust and more efficient intake of air help?

[CraigFL]

I use to race gokarts w/ 2cycle engines years ago. I'm not sure what kind of engine you will be using but I'm sure if you look for a kart supplier they will have the information to tune it. It might be as easy as enlarging/changing the timing on the ports or changing/modifiying the reed/rotary valving.

A tuned exhaust will give you more power in a narrow band, especially with a highly tuned engine. As with most highly tuned engines, the "valve overlap" will be large so it becomes very effective to tune the exhaust so the backpressure wave arrives at the exhaust port just in time to keep the unburned mixture from escaping. Since this is a function of RPM, we used to have tuned exhaust adjustable in length with a foot pedal. This allowed us to stay on the power peak.

If you wanted one easy/cheap mod to get more HP, it would be to burn alcohol. You would just need to change or modify the carb.

[BobChestnut]

Like my smartass automotive tech. teacher always tells me "The more air and fuel you can burn the more power you get".

[curtis73]

Find someone with extensive knowledge on the engine you're modifying. You can effectively change the "valve" timing of the 2-stroke by porting intake and exhuast up or down. Find out which one your 2-stroke needs for your desires and do some port work. A bit of an overbore will help provided you can find a piston, but don't go wild or you'll reduce port volume too much and make a very peaky engine.

[MagicRat]

By FAR the most important addition is a tuned exhaust, and, yes, your first post is spot0on for the basic theory.
Lawnmowers have virtually no tuned exhaust, compare its exhaust to a small dirt bike. You want to duplicate the tuning the expansion chamber gives you.

Possibly there may be kits out there, or you may be able to adapt a small 2 stroke dirt bike exhaust to the lawnmower engine, although porting would have to be modified for optimum results.

IMO you are far better off to use a dirt bike engine and trans, and build a 'shifter' cart. Since the manual trans and clutch are integral to the engine, its actually quite straightforward to build.

BTW a tuned exhaust can easily increase power by 30-50%. I know first hand by having the exhaust system accidentally fall off my 2 stroke dirt bikes and snowmobiles while riding. Noise increased a LOT and power decreased substantially.

[beef_bourito]

you could supercharger or turbocharge it, supercharging seems to be the better of the two because you don't have any unburnt fuel ging through it and it would be easier to do. get a dirtbike and supercharge it, since it already has the tuned exhaust, and run it on alcohol (if you can afford/find the fuel, might be difficult depending on where you live). I'd say you should have a good 12-15hp out of a 6.5.

If you go through with this, keep us posted and take pics.

[beef_bourito]

oh yeah, search for two stroke in aither this forum or the forced induction forum and you should find a thread started by me, someone posted a link for a supercharger on a two stroke.