What will break first

Discussion in 'Performance Mods' started by WorkingOnWise, Sep 19, 2007.

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  1. In planing my project, I reallllllly don't want to go past the 49cc limit, but I also really need at least 3hp, and closer to 4 to be realistic, to do what I want. My bike plans are discussed in the thread "Heavy Hauler Project".
    I did some quick math and found that a 49cc engine is 3 cubic inches. I have build several high performance engines, and it has never been a problem to get a reliable 1hp per c. i. d. out of an automotive engine, and still be very ''streetable" 1.25hp per cid was in reach if I was willing to give streetability and gas milage, and 1.5hp per cid was doable if I as also willing to give up durability as well. That translates into a 350hp Chevy 350, a 430hp, and 525. A 350hp 350 is a very fun engine, good power, good gas mileage (for a V8) and very streetable.
    Now, to bring those numbers to a bicycle engine, I know we are talking a 2 stroke and not a 4 stroke, but a 2 stroke will typically get you higher hp numbers that a comparable size 4 stroke.
    So, what do I not know that explains why we don't see 49cc 4hp 2 strokes? That's what I need for my project. Is it just a matter higher compression and a stronger connecting rod? I assume the crank in a typical 2 stroke in not a weak link, and in my experience, cranks fail from vibrations and lack of lube, rods fail from rpm's and compression pressure.
    If I build a super strong rod, say from titanium, and bumped the compression to 11 to 1, would I have a 49cc 4hp engine I could rely on? What would break then?

    Last edited by a moderator: Sep 19, 2007

  2. gauge

    gauge Guest

    11to 1 wow thats alot of compression to turn over u migh rip the sprocket off the spokes lol it would be pretty tourgey tho and race fuelli think is 7 dollars a gallon i would get a dax 70 , they look the same as a 50 an are preety good engines with care.

    RATRODER Guest

  4. OldPete

    OldPete Guest

    Tanaka 47R is 2.8hp in stock trim. Add their expansion chamber along with their jetting recommendation and you will prolly see 4hp. Reliable horse power at 50 to 1 oil ratio.

    Search the posts of Egor, he had something real to say about porting these Happy Time 2 strokes. If you can afford to blow one up you might end up with a real power house of an engine.
    NOTE: Make sure the rod's small end has a roller bearing and not a weak bronze bushing.
  5. Ratroder,
    I looked at those engines. If I bought one of those, I'd never be able to ride the bike, cuz, well, my very understanding wife would Kill me! $138 per hp! If I coulda charged that building car engines, I'd be set! Lol

    I didn't consider the fact that I'd have to start it somehow! At 11 to 1, pull starting is not practicle, huh? A kick starter st too much like a motorcycle. An electric starter will add to much weight, which is one reason for me not wanting to go above a 49cc. Maybe one of those wind-up spring loaded starters like what was on some briggs motors would work?
  6. gauge

    gauge Guest

    i have one of those spring loaded staters on my leafblower i hate it it sometimes gets stuck , but whats the real reason ure staing 50cc
  7. Yeah, I spent a good bit of time beating on those wind-up starters myself! I think it was wind wind wind release, wind wind bang wind release, and it started =-)

    Well, the reasons for staying under 50cc are :
    1) Weight - I need to be able to carry the bike up and down stairs.
    2) Physical size - I don't want to have to hack and grind on the bikes frame.
    3) Efficiency - gas mileage
    4) legality
    5) The "wow" factor of being able haul the whole thing around at 30mph, getting 120+ mpg from a weed whip!
    Last edited by a moderator: Sep 19, 2007
  8. dbigkahunna

    dbigkahunna Guest

    One of the Honda/Clone 4 strokes should have the umph you are wanting. You need torque more then HP. You will be sacrificing speed for torque. Check out http://davesmotors.com they have some below 49 cc engines cranking our 4 plus HP.
  9. gauge

    gauge Guest

    (dahbigkahuna )he wants a light weight bike so 4 strokes are out of this discussion, but does anyone know the diffrence in weight betweeen the dax 50 and 70
  10. gone_fishin

    gone_fishin Guest

    i don't know but i suspect the answer is "no difference" or "insignificant."
  11. azbill

    azbill Active Member

    very little
    a couple ounces or so
    they look/feel weightwise almost identical
  12. gauge

    gauge Guest

    well then i till say the dax 70
  13. 247Jude

    247Jude Member

    I was thinking of the same thing, I was going to port it, and get a tuned exhaust. With a 50 tooth sprocket, should be able to throw a little mud with that.
  14. DetonatorTuning

    DetonatorTuning Active Member

    Daves Discount Motors, GP460. 4.2HP totally stock, 8#'s CCW on the left side, pullstart.

    $250.00 + shipping

    Staton, 3000rpm HD clutch engagement springs. must have, don't bother with this engine without them.

    pull starter upgrade from "chevys4me" over at gopednation.com, highly recommended.

    good luck,
  15. Easy Rider

    Easy Rider Guest

    I agree Steve. The 460 motor is decent but I know when they first came out, the chrome plating on the cylinder walls would peel off and the pull starters would last about a week of you were lucky. The pull starter is really recommended. Being stranded because you can't start your motor really sucks. Chris (Chevys) he knows 460 very well and he builds and ports some of the fastest 460s around.
  16. fetor56

    fetor56 Guest

    Any other mods that need doing to this engine besides the pull-start & clutch springs...i'm also assuming the chrome plating problem has been fixed?
  17. DetonatorTuning

    DetonatorTuning Active Member


    i'm a participant over on gopednation.com where these engines are very common. you can find many posts in the archieves about the poor quality of the cylinder plating from the very start.

    over the years, the incidence of failures due to the plating has slowed to a near standstill, though there's no guarantee it couldn't happen.

    following a conservative premix ratio with very high quality synth oil seems to be the best insurance. i'm using amsoil saber mixed 65:1, 1.25 turns on both needles.

    i changed my base gasket from the stock .020" paper to a .005" copper gasket and picked up noticable midrange torque.

    to the point, i'm not aware of anything else this engine needs other than a drive system that can handle it. this engine also prefers atleast 21-22:1 overall gearing on 26" tires.

  18. fetor56

    fetor56 Guest

    I won't be ordering the engine immediately cos i'de like to see how 5-7's friction drive turns-out(particularly with Dominator pipe)
    In the meantime i'll check out that website for further info.......thanks alot man.
  19. DetonatorTuning

    DetonatorTuning Active Member

    the Dom. is not going to be a real factor. it lets the engine rev. further into the rpm range and delivers another couple mph's.

    at 15:1 not a chance, 13:1 doubtful, 11:1 slim posibility with lots of sacrificial operating compromizes.

    see my thread "biggest engine on friction drive ?" for some good comments and points from experienced friction drive users.

  20. fetor56

    fetor56 Guest

    Will do,taa man.All this stuff isn't as simple as what u might think & i'm hoping the Oz$ will continue to claw it's way UP.....WAY UP. :grin5: