Grubee engine; made for speed (NOT!)

Discussion in 'Performance Mods' started by jaguar, Dec 6, 2011.

  1. jaguar

    jaguar Well-Known Member

    Here´s the 8 reasons the engine is weak;

    1. carb has no true idle jet which causes loss of power at all rpm´s
    2. head compression is too low
    3. intake and exhaust ports are too narrow, and intake is too high
    4. transfers are too narrow so that attempts at turning the engine into a high rpm screamer fail
    5. crankcase compression ratio on the 48cc is only a pitiful 1.1 which provides only 1.5psi when the pistons uncover the transfer ports. Such a low pressure greatly limits power. 3psi is the bare minimum needed.
    6. CDI does not retard the ignition timing at high rpm´s which limits power and creates too much piston/cylinder heat. It also produces a very weak spark.
    7. piston/piston-pin weight is not correct to match the counterbalancing of the flywheels which causes upper rpm engine vibration which limits power.
    8. The exhaust is just a straight pipe with muffler. The lack of a true expansion chamber limits both low rpm grunt and high rpm speed.

  2. oldnube

    oldnube Member

    Whats A Person To Do?

    What steps can a person take to correct this or how can we get the most from these HT engines safely without causeing damage to them?
  3. motorpsycho

    motorpsycho Active Member

    ummm, junk the h.t. engine and use a chainsaw engine?
    Really, these h.t. engines were not designed to be high performance screamers.
    they were built to do a very simple task, and that's to get a bike to move.
    if you want true high performance, a h.t. engine would have to be totally re-designed.
    if you want to improve the performance of the h.t. engine, it can be done, but don't expect to get a large horsepower increase simply because of all the things that jaguar mentioned.
    if you really want a powerful, high revving rpm monster, a 50-80 c.c chansaw engine with reed valves, and an expansion chamber would be the way to go. but then again, with this much power you would be breaking parts on the bike left & right and you would need disk brakes to stop the thing.
  4. jaguar

    jaguar Well-Known Member

    Please click onto my signature link to read about how to correct these problems.
    You can greatly improve the performance with my suggested changes. You won't make a 48cc non-reed-valve engine truly HOT but you will be surprised at how much more power you can get from it.
    Best thing I ever did is put the 58cc top end on it and custom fit a reed valve to it. People who try it say it's more powerful than any moped of the same engine size. It's still one speed with a 44 tooth sprocket and I have to put the brakes on when I arrive at my house although it is on a steep hill. I have more power now than I thought I would ever have.
  5. Cavi Mike

    Cavi Mike Member

    It's a $150 turn-key kit. Did anyone really expect some marvel of engineering here? You could buy 2 of these kits for less than one Robin, engine only.
  6. jaguar

    jaguar Well-Known Member

    It's not a question of engineering or expense (somewhat). They designed it for low power so it would pass regulations in all countries. Now it's our job to make a real engine out of it.
  7. HeadSmess

    HeadSmess Well-Known Member

    no se puede pulir la mierda

    when the HT was first designed i dont think there were any regulations in any countries, including the state of california.

    designed to a budget, built to one.

    can get one to scream, and then to blow up dismally.

    can leave one the $#^% right alone, it blows up dismally...

    they blow up.

    no modifications you make can fix the basic design flaws, starting from choice of materials.

    (they are still fun though)
  8. Neon

    Neon Member

    HeadSmess quit swearing even if it is in Spanish.
    Why are people always trying to turn Hoovers into Jet Engines?
  9. jaguar

    jaguar Well-Known Member

    not a jet engine, just something that works like a 2 stroke should.

    "no modifications you make can fix the basic design flaws"
    I disagree. By changing the flawed parts then it is fixed.
  10. geebt48cc

    geebt48cc Member

    Jag, I really like they way you think. Jag, do you mean where the intake is located on jug, or the rake of height of intake to carb? Is the straight intake from jug to carb the best?

    Last edited: Apr 2, 2012
  11. jaguar

    jaguar Well-Known Member

    I mean the bottom edge of the intake needs to be lowered a tad. Details are on my site.
  12. DeathProof

    DeathProof Member

    my grubee is awesome its a 66cc been up to 40kmh and i drive the craap out of it and woulnt want anyything better. its a bicycle not a motorcycle so stop complaing and enjoy it
  13. ddesens

    ddesens Member

    "its a bicycle not a motorcycle so stop complaing and enjoy it"--I agree with this totally.
  14. Lunardog

    Lunardog Member

    The stinger I bought is just getting broken in, but even stock on a level surface I have to decelerate at the throttle because it will exceede rpm's it should turn to run to last. Living in Pa. it will climb 8 and 10 % grades with some minor assisted peddaling and I'm at around 185 lbs. A little more lower end torque might be nice but this could be accomplished by raising rear sprocket size I'm sure. Since I want this thing to run when expected right now I think I'll skip the speed/power mods. But I could definately see in the near future building a Bonzai bike just to see whats possible. May be pickin your brain then Jag.
  15. jaguar

    jaguar Well-Known Member

    But my focus hasn't been on making a kamikazi bike. The intake and exhaust extensions were for more low end power. The piston ramps were for more mid range. Increasing compression is for more power all around. Reed valves give more low end power boosting on these engines although with the right tweaking you can also get more top end. My engines, except for my latest project, have only been ported for a limited increase in rpm. I also invented the extended baffle expansion chamber for a low end boost. My vibration cure affects mostly mid range. Until recently I was living way up in the mountains and there were many inclined streets. I developed what was necessary for these engines to be better hill climbers, not road racers. What worked for me I shared on my web site.
  16. DeathProof

    DeathProof Member

    i hear alot of complaining from ppl expecting these engines to keep up with harleys or porches FFS its a tiny engine built to make our biking fun without the peddling it aint a souped up engine its a frickin 49 and 80cc engine just STFU and enjoy it and stop the crying my grubee is 80cc and i aint looking to break no land record just a new toy now dry ur eyes and buy a motorcycle if it aint fast enough for you!
  17. HeadSmess

    HeadSmess Well-Known Member

    ok, i admit, ive slagged em off a lot too.

    but i use one still. or did. its leant forlornly against the shed, on top of several frames, crying to itself...

    i feel sorry for it sometimes :(

    but... for the price they are, theyre excellent. a few tweaks makes them enjoyable, and anything more makes them...touchy. but whatever.

    now i dont rely on them, im all for the kamikaze death rocket! i got 84 once downhill! that was with minor tweaks! so what will major mods do? :eek:

    but, as interferes with the best laid of plans. so.

    grump. here i go, talk talk talk... i should be in my shop, but its cold and has no heating.

    im really good at making...excuses!
  18. DeathProof

    DeathProof Member

    oops *porshes
  19. jaguar

    jaguar Well-Known Member

    deathpoof, you obviously have not rode a 48cc. The poor thing is begging for help on its knees it is so weak. I can't see anyone content with it other than an 89 year old grandma. From what I've read the 66cc is not too badl.
  20. DeathProof

    DeathProof Member

    yea the 49cc is built for kids and elders i think lol but the 66cc is great sometimes its 2 fast i dont even do full throttle mostly 60% throttle and im cruisin pretty good.