Tuning the KTM 380 Barrel / Piston / Head

Ivan K

May 23, 2001
greets from austria & sorry for my bad english

hope i´m in the right column with my stuff...

my bike: KTM 380 ´99 2 Stroke (Supermotard-conversion - you know, the small wheels...)

finally i did it - competing in supermotard-races...the result was: driving is fine, but the bike-engine is TO WEAK compared to others on the track.

anyone ever tuned a 380 engine ? i´m thankfull for any information.

my plan: a few aftermarket-products combined with a porting job on the barrel, some mods at the cylinder-head for higher compression-ratio, making the piston "fitting" to the porting work, setting up carb and the TVC very correct etc etc...

in my thoughts were some after-market products like:

*an FMF-Fatty

*Delta II Reeds

*a forged piston (wiseco?)

my questions:

is it possible to insert a forged piston into a barrel which once run with a cast-iron piston ? there should be a rebore before, right ?

porting work: ANY ideas ? anyone ever done something on that barrel ? anyone here who can give me any useful porting-times, any angles or any other useful data, so that I don´t have to start from ZERO.

needed is more top-end, but more torque would also be VERY FINE ...

the work is going to be done from a very good italian 2stroke-tuner (up to now he doesn´t know from his "luck" that he will make the job *smile*).

problem is that this guy never worked on that kind of bike, so I want to bring him as much pre-information as i can get for him

I hope someone can help me.

hope to hear from you !

thx !!



Aug 13, 2000
I cannot really help you with port specs, However I run a Husky 360 on the street. It was an "enduro" engine with mild port timing. I ended up running 194 degrees of exhaust port duration and 134 degrees of intake port duration. I am doing this by memory so forgive me if I am off a little. The bike has an FMF fatty pipe that was also tuned for the enduro engine. I ended up shortening the headpipe by 25mm. This was to get the pipe tuning in sync with the port timing. I used a couple of programs to determine the pipe specs along with a question posted to Eric Gorr.

My bike is fairly quick now and really revs out. It makes about 55HP at the rear wheel. You may be looking for more. I am happy with the power, however the need for more is always there!



Dec 14, 2000
Ivan, greets from Spain & ALSO sorry for my bad english!

I am a KTM 380 enthusiastic, I have tuned my 99´380 SX myself.
I continue working in the engine, but now:
I have raised compression ratio and reduced squish clearance,I have polished head chamber and piston crown, I have a Wiseco piston ( one ring, more light), all cylinder and crankcase ducts are polished and fited,I have increased main and secondary transfers width and boost transfer timing, I have worked very much in the exhaut ports, modify the timing, widths and shapes, in the secondary exhaut ducts is very important to fit the control rollers to the ducts, I have a whole Spes exhauts system ( I ride motocross) and I have worked in carb. polished, rejeted and overbored ( 39.5).
Yesterday I bought a Boyesen Rad Valve, but I haven´t tested yet.
I want work soon with ingnition maps of Wolf CDI unit to fit to this modify.

The bike is very much power than standart, Ivan contact me to details


Aug 13, 2000
I was thinking about your supermotard bike today. I wanted to share my personal opinion about port timing and off road engines. I find that off road engines need a wider torque curve and therefore milder port timing. This may be due partially to the lack of traction and wheelspin. On road 2 strokes do not need as wide a torque curve. The engine can be setup for a torque curve that is just a bit larger than the RPM drop per shift.

My example could be a RPM drop of 2000 RPM between 3rd and 4th gear shifting at the top of the "powerband". With a torque curve centered around 7500RPM and 2500RPM wide. This will allow the engine to stay on the pipe in every gear without dropping below the torque curve.

I believe an on road only 2 stroke can be modified beyond what the same engine could be for dirt only.



Mod Ban
Dec 10, 2000
cujet, I have to agree with you, street engines can be run in a higher state of tune than dirt-only engines. This is the reason that shifter carts, with the same Japanese two-stroke engines that are used in our bikes, make considerably more power than they do in bikes. These engines are very peaky, with a torque curve that would be unacceptably narrow and brutal in the dirt, but the traction of pavement, and the gear ratios used for the carts, make this a non-issue.
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