Tuning the KTM 380 Barrel / Piston / Head

Joined
May 23, 2001
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#1
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 !!

Ivan
 
Joined
Aug 13, 2000
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#2
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!

Chris
 
Joined
Dec 14, 2000
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#3
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
 
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#4
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.

Chris
 
Joined
Dec 10, 2000
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#5
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.