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Dirt bike engines in GP bikes?

Discussion in '2-Stroke Machines' started by killerofangels, Apr 26, 2011.

  1. Tdub

    Tdub Say what???

  2. zrx12man

    zrx12man Captain Amazing

    TDub, actually, I took some of these concepts a step or two further by using my Craftsman 1 3/4" hole saw to remove most of the piston crown on our A bike, thus improving the flow characteristics of the top end to match the New Reed (edges meticulously chamfered with my best wood rasp to remove potential stress raisers, of course). This also has the added benefit of reducing reciprocating mass, allowing me to remove the balance shaft completely and plan for a rev limit around 23,500 rpm.
    Dyno testing to follow, I fully expect to see 78-79bhp at the wheel on 87 pump mixed 80:1 with Craftsman weed wacker premix.










    too much? :D
     
  3. Tdub

    Tdub Say what???

    Hell no...sounds like you are on the right track!!:up:
     
  4. badger278

    badger278 Member

    Maybe I'm old fashioned, but I'm not sure why anyone would want to put another motor in a 125 frame. RS-125's are still readily available, cheap to run and they don't bend valves.

    I understand the 'waki 250's as a replacement four stroke, but for my money you can't beat an RS-125. $3,500+ can get you a good running 98+ bike...
     
  5. zrx12man

    zrx12man Captain Amazing

    I agree, dunno about the whole "cheap to run" deal, though....
     
  6. badger278

    badger278 Member

    cheaper than top end rebuilds...
     
  7. Tdub

    Tdub Say what???

    You are kidding right??? Have you priced an HRC piston lately? Forget the aftermarket ones, they are crap. RS rebuilds are required every 300 miles...a 250 topend 2-3x that. A good Hotrod will outrun ANY 125 on the grid...2009 proved that! Next!
     
  8. badger278

    badger278 Member

    Last year I ran 9 or so events. 1,000 miles total. One year end rebuild and 3 top ends. No unexpected issues. Finished every race.

    I still think 125's are cheap to run... Maybe I'm delusional.

    How many valves did you bend? ;) How many ruined heads?
     
  9. zrx12man

    zrx12man Captain Amazing

    Dang, we go through a top end ($350 or so) every weekend per the book, and a bottom end ($1050) every 4 weekends, plus various other consumables (reeds, O-rings, chains, etc.), so for 9 race weekends we're looking at around $5500 just to keep the motor happy.

    Dammit, I wish i hadn't done that just now. :(
     
  10. badger278

    badger278 Member

    What??? You are way over doing it. I change rings every 150 miles, pistons every 300, and a bottom end at 1,200 miles. Reeds every other race weekend.
     
  11. zrx12man

    zrx12man Captain Amazing

    maintenance

    We follow the same schedule, but we do Friday trackdays before the races as well, so we get a lot more track time than you do.
     
  12. Tdub

    Tdub Say what???

    Uh... none.
     
  13. turner38

    turner38 Well-Known Member


    Zero.
     
  14. Dragginass

    Dragginass Well-Known Member

    I'd like to have another 125 or 125/25of hybrid sometime soon. For those of you in the current know, would I be better off finding a used Moriwaki or find a used RS125 and do a conversion?
     
  15. behindthetimes

    behindthetimes Active Member

    When Honda was testing their little I4 125cc fourstroke back in the day, they couldn't keep up with the Rumis and Kreidlers.He was using 17,500 rpm as his shift point.After a few hotter laps he came in and said he was shifting at 21,500.My Dad was there at the airport track at Daytona,before the banks.He rode for Montesa.
     
  16. behindthetimes

    behindthetimes Active Member

    They never did make it competitive. But it led to Hailwoods 250 6's in the 60's.How much HP does Honda's new 250 make?
     
  17. anand

    anand Well-Known Member

    then you also have zero power:rolleyes:
     
  18. turner38

    turner38 Well-Known Member

    Really dumbass?

    If you are having spring and valve failure you need to take a serious look at your engine building skills.

    The Hot Rod went a full season with ZERO valvetrain failures while producing the power neccessary to compete with and beat the Aprilia's of Veloce racing.

    So the reality is I have considerable data to support my claims. What do you have to support your claims besides bullshit? ( where's the FU icon when you need it?)
     
  19. Tdub

    Tdub Say what???

    :stupid: :up:
     
  20. anand

    anand Well-Known Member


    so you have more power then the official honda moto3 bikes :crackup:

    change that centence to "Less Reality More Bullshit"
     

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