Expansion Chambers are Incredible!

Discussion in '2-Stroke Engines' started by flashstar, Oct 1, 2010.

  1. flashstar

    flashstar Member

    I recently bought a Sick Bike Parts expansion chamber for my 70cc 2 stroke happy time. I also picked up a billet intake and high flow air filter at the same time.

    I didn't really get a chance to open up the throttle until today when I had a short break from school work. The first thing that I noticed was that even after sitting for 4 months over the summer, the engine turned over immediately with the expansion chamber.

    The second thing that I saw was that the engine was running fairly rich even though I had a .66 mm jet installed. Even while running rich though, the engine already allowed me to climb hills at 24-25 mph that I could only ascend at 15 mph before I got the expansion chamber!

    Today, I pulled the carburetor apart and swapped out the .66 mm jet for a .64 mm jet. Suddenly, my HT was beating my 50cc Huasheng motor on my other bike. Now the little 2 stroke pulls even at 30 mph with a 40 tooth sprocket. The only main downsides to the expansion chamber are that it is fairly loud and that I cannot find a place where it doesn't rub against my rear tire or pedal.

    Regardless, this product is highly recommend. I also recommend purchasing the billet intake and high flow air filter at the same time.

  2. HeadSmess

    HeadSmess Well-Known Member

    i agree. the most dominating influence on a 2-strokes performance you can make, with the correct jetting.

    heres my dodgy homemade.

    doing the brutal cut n weld on the end of the diffuser cone/straight section affected the band somewhat, and migwelding stainless... :lol:

    but the gains are huge... pulls my mate up my local teting hill at about 40km/h, and hes around 100kg... it gets me up at 55 :D thats now the cruising speed.

    the next model is going to be mandrel formed up in pipe, tigwelded, then sand bent to shape. get rid of all the sharp corners and nasty welds... then once i work out a reliable method...sell them.

    its interesting to compare the geometry between mine and sbp.

    ive proven my geometry works on at least five engines.
    to me the sbp looks... im not saying anything. :)

    Attached Files:

  3. asfazrq

    asfazrq Member

    I agree too. I bought an expansion chamber from SBP and it came in with moving (eblow, exhaust header etc) were too tight and would not move. I got really discouraged and was on the verge of returning the thing. I am super glad I didnt. Jim came to the rescue from SBP and provided replacements parts. Not only that he cut the exhaust header for me. I noticed quite a decent improvement. I am running on 36T sprocket and the bike runs awesome. I would highly recommend this upgrade to anyone who does not have it