horse power mods!!!

Discussion in 'Performance Mods' started by ultimusmaximus, Jan 14, 2008.

  1. ultimusmaximus

    ultimusmaximus New Member

    in the process of modifying... i just added a $120 dollar performance hp carburetor kit with velocity stack and uni air filter which went together perfectly with minor machining... so stoked... i also ported and skimmed the cylinder head... again worked out very nicely, especially since my dads got a metal lathe in his garage... also added big nobby off road tires and mud fenders for the off road am waiting for super performance hp expansion chamber exhaust pipe ($109) to come in the mail which will be here in a few days...then i will post pictures and let everyone know how it worked out.

  2. kerf

    kerf Guest

    Nothing like a box of new toys to get the adrenalin pumping. I know it always works for me.
  3. srdavo

    srdavo Active Member much did you *skim* off the head? I had one milled down .030 (I'm still testing it)
  4. HI,

    Wow....that is exciting....I am definitely interested in seeing what performance gains you get!....Just curious but what kind of pipe did you end up getting?

  5. ultimusmaximus

    ultimusmaximus New Member

  6. ultimusmaximus

    ultimusmaximus New Member

    i forget how much we skimmed down but it wasnt too much proly around .050... first i took off the cylinder base gasket and replaced it with high temp rtv gasket material and then skimmed the cylinder slightly
  7. ultimusmaximus

    ultimusmaximus New Member

    you guys can check out the finished bike in the picture gallary under the thread that says "horse power pipe and carb dirt cycle" ... there are pictures and descriptions of the performance!! let me know what you think
  8. Haggard

    Haggard Guest

    Howdy fellas.. Ive been using expansion chambers for quite a while now.
    By changing the header pipe length, )between the flange and the expansion chamber) You can dial in your 2 stroke power band to what ever rpm range you like.
    A 2 stoke power band rocks compared to a 4 stroke but is optimum for a vary small rpm range which is why the pros tune a pipe to get the optimal power wheres its most benificial according to what tipe of track there running and their riding style.
    Also the length of pipe behind the expansion chamber , known as the stinger can be manipulated real well also.
    I'll keep this short and simple .
    You'll notice a tuned pipe uses a baffle rather than a muffler or soetimes just a stinger.
    Heres what I do.
    I know that to have good bottom end, a certain amount of back pressure is needed so I use some regular run of the mill orange house insulation , and wrap it arount the end of the stinger pipe `(that has holes drilled) and put the baffle back over top of the insulation. I wrap it pretty good so thecavity is pretty much full.
    This not only gives it a real nice throaty sound but I'd guess up to a 15% exceleration boost.
    This would work real well ona shorttrack but unfortunately , this back pressure is going to cost you in the higher rpms where a straight stinger following the chamber will give much better top and speed and higher rpms.
    I've ben known to adjust my exhaust back pressure a couple times a day depending on whar I was up to.

    Any ways my idea is to make atunedpipe with expansion chamber but add a choke per say behind the exhaust chamger that could be manipulated to breath better as You go throw the rpm range , Even just a gear changer and cable to keep it simple/.
    .Imagine a powerband that will take you threw a range of 3000 rpm instead of just 7 or 8'''hundredrpm.
    An alternative is to do some testing with a couplesprings and see if you could get this restrictor plate to work automaticaly from the increase/decrease in p[ressure caused from accel'deaccell.v

  9. Now I remembered back in the day I had an RM 250 and when I ran it the powerband..AHHHHHH!!...AAAAHHHHH!! between every shift.

    Is this what you mean when you say 2 stroke powerband? Can a happy time actually get a powerband similar to that with an expansion chamber?
  10. iv ran my mb with the baffle out, cant be too god for it because it sounds like children being eaten, but did pick up some good midrange to high end HP
  11. Sounds just like a Powervalve, right?

    I'd love to have an aftermarket power valve for these little 2 strokes.
    Has anyone put an intake reed their Happy time?
  12. fastboy9

    fastboy9 Member

    Bored my jet, expansion pipe, matched ports.
    At work I've got a milling machine so I want to mill the head, in millimetres how much should I take off?

    And also what other things could I make with the milling machines and lathes?
    hmmmm.... ideas!
  13. Mountainman

    Mountainman Active Member

    not sure about yours ------- but

    not sure about yours ------- but

    baffle taken out --- has been known to bring some to the point of


    I hope not because it's best when both wheels are turning when we

  14. BSA

    BSA Guest

    I heard you can take of safely 10 thou for certain. I know some people have removed much more, but each engine is different.

  15. fastboy9

    fastboy9 Member

    Ill give that a go then, about quarter of a millimetre
  16. tacoshell4

    tacoshell4 Member

    you put that carb on a ht? what kind of mod did you do to install it? there is a little hole in the carb where the gasket goes as well as a little hole in the gasket. That is for the crankcase pulse. how did u make this carb work?????