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Boosting two stroke power

  1. Jan 11, 2016 #1
    Hi :
    My name is mike and I am a avid Formula 1 go kart driver. I have been pushing the limits of my F1 kart and want to increase my performance of my 250 CC two stroke engine and enjoy the excitement of insane speed one inch off the ground. Anyone into F1 Shifter Karting please let me know.
    thanks Mike
  2. jcsd
  3. Jan 11, 2016 #2
    Welcome to PF!
  4. Jan 18, 2016 #3
    What kind of engine? There is a ton of mods to do to 2-strokes, not sure what the best is for a kart. For dirt bikes, head mods (set squish and compression) are the best bang for the buck. After that, usually carb mods (bore and divider plate), pipes and porting are what you go to next.
  5. Jan 19, 2016 #4
    I have a 250 CC honda moto cross 2 stroke 5 speed engine on a shifter go kart. It is a lot of fun. I am familiar with the suggestions you have mentioned. Right now the engine is set up with a carburetor. I was thinking I may want to try fuel injection, something like throttle body and perhaps supercharger or turbo charger. I am not sure if boosting compared to naturally aspirated may worth the trouble. I am not sure if I would want to use a divider plate if I use a throttle body fuel injection. Any thoughts you may have would be appreciated. My hopes are to get to somewhere near a top speed on the shifter kart of 140 to 150 MPH.
  6. Jan 19, 2016 #5
    I have looked into boosting 2-stroke snowmobiles in the past, there really are not any turbos (or superchargers) available that are small enough for a 250, at least in the past when I looked into it. Boosting a 2-stroke can be pretty tricky.

    I always wanted to fuel inject a 2-stroke, if you are committed to it, I don't think it is too bad. Look into Megasquirt ECUs.

    140 to 150 in a kart, not for me:)
  7. Jan 20, 2016 #6
    Look into changing the expansion chamber (tuned pipe).. there is a MASSIVE amount of math required to design them properly, but they are the key to 2 stroke power. I think EFI might be hard to implement since O2 sensors will get all confused by the scavenge air, so closed loop and feedback of any sort is out... You would probably be looking at an Alpha-N mode instead of speed density.. so you'd base your fueling solely on TPS and RPM, not on manifold absolute pressure (MAP) and RPM. Megasquirt is probably the ECU to look into, I think it's the most customizable, at least from a DIY standpoint.

    About expansion chambers, TANSTAAFL.. there ain't no such thing as a free lunch... I don't know what kind of power band you have currently, but you can tune the chamber for a nice wide band, of if you have close enough gears, a violent boost of power over a narrow RPM range.

    I have been playing with 2 stroke tuning for a bit.. Since they're cheap, I do it with chainsaws.. Here is a bored, stroked, ported and piped Husky 61 (48x34mm is now 52x36mm bore/stroke) now at 77cc... I designed the pipe, and I could get more out of it with more aggressive exhaust port timing, but I want it to be usable without the pipe too... Originally the saw had about 3.5hp, it's probably around 8hp now... Peak power is around 11,500 RPM, peak torque at about 10,500RPM. That is a 34" bar (They usually had 20" bars)

    It's a lot of fun, just be prepared to need new pistons and cylinders.. when you start pushing really hard you've gotta count on blowing some up.

    Oh, and keep the sticky side down!
  8. Jan 21, 2016 #7
    Cool! Nice video! I take it hearing protection is required? haha
  9. Jan 21, 2016 #8
    The exhaust coming from the 'belly' of the expansion chamber actually quiets it down a lot comparing to taking it from the end of the baffle cone.. I tried both and it's quiet in comparison... yes, hearing protection is still needed.
    It was a fun project to do, stroking it was hard to do, the overbore was easy with the top end of a different saw (husky 272)...
  10. Jan 26, 2016 #9


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    Perhaps try high nitro fuels as used for the stroke model aircraft?
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