CR500- Road Race bike

Discussion in '2-Stroke Machines' started by JTRC51, Aug 31, 2015.

  1. 90kacoupe

    90kacoupe Novice seeking Help

    I understand! Building and tinkering is half the fun for a lot of us. That is why my first race bike is a vintage 2 stroke. I'm learning a lot with it and would love to take on a modern 250cc MX powered 2T GP bike project. I do like the simplicity of a single cylinder 2 stroke race bike.

    Sent from my SM-G930P using Tapatalk
     
  2. Cybernaut

    Cybernaut Well-Known Member

    not sure if you are aware of this but a properly built 2002-2004 CR250 will kill a CR500 on a road course and they don't destroy frames, it does take a lot of work to get there.

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    TurboBlew likes this.
  3. NOLAracer

    NOLAracer Well-Known Member


    What kind of HP numbers are we talking?
     
  4. Cybernaut

    Cybernaut Well-Known Member

    Well a strong real world CR250 will pull about 64 hp at the wheel, but the bigger picture is it will do it and survive the extended WOT required in road race conditions. another 4 or 5 can be obtained but you will pay a very heavy price in reliability.
    Also you should consider that although a CR500 is a beast and I had many, they have been designed for MX so constant on/off throttle application , they will never make more then 70hp at the very max and they heat soak and fade bad too.
    2 stroke engines reach max cc to hp right around 110cc that is why GP500s were designed around 4 125 cylinders. Not matter what Honda did with the RS 500 3 cyl they could not match a 4 cyl 500 because of combustion chamber size, so Honda had to go to the 4 cly 500 style of motor. So a single 250 can't match a 125 in terms of peak power based on efficient combustion, this is why a 500 single 2T while being a toruqe monster does not do that great as a RR motor and man what a pain to jet , and re jet during the morning to afternoon and not burn it down.
     
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  5. 90kacoupe

    90kacoupe Novice seeking Help

    I do know 250cc superkarts are around 60hp reliably. If a 200lb bike could be built with a 60hp 2T single, you will probably have a reliable and very easy/ inexpensive to maintain "GP" bike. I may give this project a go before to long. My vintage bike is really fun, but I would love to give a modern 2T a go.
     
  6. Kurlon

    Kurlon Well-Known Member

    I was happy to see low 40s at the wheel out of my 250 in my sumo, mid 60s would be crazy fun.
     
  7. Cybernaut

    Cybernaut Well-Known Member

    yes it is but you need a stack of combustion chamber inserts and other goodies , custom built reed cage,intake track, and on and on, special mapping as the Honda map is a joke
    no power valve and totally reshaped and sized exhaust track and a hand built pipe.
     
  8. Cybernaut

    Cybernaut Well-Known Member

    BTW only the CR tranny and KTM will take the roadrace loads all the other jap motors eat tranny
     
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  9. Kurlon

    Kurlon Well-Known Member

    No power valve, how big of an impact on midrange does that have? (He asks as he pilots a bike that almost half the power valve has been ground away anyways due to the big bore setup...)
     
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  10. Cybernaut

    Cybernaut Well-Known Member

    nothing much below 6000 rpm , reasonable mid still very ride able , you will be using lots of clutch from a dead stop
     
  11. VFR#52

    VFR#52 Well-Known Member

    A CR 500 makes so.much torque it dont need a power valve.
    My make power at crack of throttle.
    Now i will say they dont like to rev and best if you grunt it.
    But 70 is easy to get.
    But in RR application gearing is key.
    Getting it tall enough has been problem when motarding them.
    And i add 28 oz weight to mine.
    Smooths out power and makes traction on anything.
    Now a 250 will have to be revved to make power.
    Also with a new style carb jetting is not big an issue.
    On my dirt bike slash woods bike i run 15 49 and it idles down track no problem
    My motor is in a 98 CR250 chassis and i also solved the vibration issues they have had.
    Motor super reliable and just plain rocks.
    Hell on a dirt bike track i can use 1 gear all way around it unless they have a really long section.
    Best of luck.
    Also i can install motors in chassis for a fee.
    Best of luck and love all the project's you guys share.
    Steven Isenhower #52
     
  12. Sweatypants

    Sweatypants I am so smart! S-M-R-T... I mean S-M-A-R-T!

    went and talked to fab shop today and we threw some ideas around. gonna stick with the YZ frame, its not as bad as they made it sound at first.
     
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  13. 90kacoupe

    90kacoupe Novice seeking Help

    Cool, I'm looking forward to seeing the progress!
     
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  14. 90kacoupe

    90kacoupe Novice seeking Help

    So what do ya'll think of this..



    Seems to be a decent option really. Looks to be built on a 97-99 CR250 chassis. This chassis was known for being to stiff for a MX bike. I would thing that would work in its favor as a GP Machine.
     
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  15. mattology

    mattology Well-Known Member

    hahahahahhaa that video is great
     
  16. 90kacoupe

    90kacoupe Novice seeking Help

    The music just makes it even better!

    I think I am about to pull the trigger on this build. I need to source a front end and wheels. A shock shouldn't be to bad to find. I have been wanting to do this for a while.
     
  17. britx303

    britx303 Plagued with FZRs...........

    Have you been able to get this on track yet? Which classes are you running this in?
     
  18. Sweatypants

    Sweatypants I am so smart! S-M-R-T... I mean S-M-A-R-T!

    not even close. engine in line at Jerry Hall's for like 2.5 months already, supposed to start it end of Feb. so however long that takes. fairings are mounted. gas tank being made next, gauge cluster mount and stuff. whenever engine comes back, fab up the exhaust and carb intake (i have a huge order of titanium supplies sitting in my basement ready to go), modify the powervalve (could be fairly easy or ridiculous, not sure yet), wiring and tuning, then a bunch of little shit like the shift linkage, battery tray, etc... so i guess Jerry is probably gonna be the long pole in the tent, which is fine, but then i really have no idea how long that will take until i see my motor back again, and even after that it'll be a few months of stuff.

    then need suspension tuned cause its way off as is (forks are from an R1 LE, this bike weighs like half). then paint and powdercoat. probably not gonna be until next year honestly. i'd like to be taking it to GMD or the like towards the end of the season next year if the timing can work out to get that sorted and be ready to go for spring.

    and even then, no idea... whatever mongo let's me? i don't really care about making some great career of racing, i just want it to be competitively close to whatever else is on the track. clubman? F2/3? F500? SV650's? beats me. its going to have a modified swingarm/frame, engine from a different company, full on forks, full on brembos... so either that'll throw me into obscurity, or maybe mongo gives me a pass on a few rules just to get me out there? no idea. i dunno if i'll even race it next year, maybe just some track days at first? i have literally no idea what to expect even with what the riding experience will be with this thing. it'll be nice to get some time under it in a test & tune sense before actually trying to race other people and be competitive. nothing i hate more than going to the track and spending half the day messing with shit cause something isn't working right. i learned that lesson with cars long ago and i'd rather be like, "ok... suspension is pretty good or in the ball park, carb tune is good and runs good, and have some idea how the tires with grip and bike will handle". most aggressive i've ever had so far is BT003's. i'd like to try slicks on this thing, but would be new to the sensation. i'm gonna put some tags on it and NOT slicks at first, so at least i'll be able to ride around the street from time to time and get some time on the thing and feel it out, but we'll see. its moving along though at least.

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    Last edited: Feb 3, 2018
    pscook and 418 like this.
  19. britx303

    britx303 Plagued with FZRs...........

    Hope it works out. I thought you had a class in mind and were building the bike around that.
     
  20. Sweatypants

    Sweatypants I am so smart! S-M-R-T... I mean S-M-A-R-T!

    nyeahhh... i just wanna have fun and i wanted something 2-stroke, light, one-off... that i could just keep forever as my own creation. even the next idea i'm already formulating will be another 2-stroke hybrid. there's not much for that kinda thing in the regular structure. maybe i'll go get an R6 one day again, but for now i just want brappps and to maybe wee myself a little. if that means trackday, that's ok by me at this point in life.
     

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