China girl 66... Maximum RPM?

Discussion in '2-Stroke Engines' started by buzbikebklyn1, Jun 16, 2011.

  1. buzbikebklyn1

    buzbikebklyn1 New Member

    Hey guys... I had a customer today ask me what the maximum safe RPM for a China girl that's been broken in and is in good shape?
    I had no definite answer for him!
    I set up my bikes for low end torque not high RPM power, so I never spin mine much past 5,000.
    Consequently the engine lasts longer... I know they are capable of higher RPM but why stress the engine?
    Who's got the correct rev limits?
    BBB
     

  2. gothicguy64

    gothicguy64 Member

    hi

    according to z-box

    specs of 66cc

    1. Engine Type: Single cylinder, air-cooled, 2-stroke
    2. Type of fuel mix :(16:1/20:1)
    3. Displacement: 66cc
    4. Ignition: C.D.I. ignition
    5. MAX.Power: 1.7kW @ 5500rpm
    6. Economy: 100 km/1.5 litre fuel
    7. Nominal speed : 30-35km/h
    8. Fuel tank: 2 litre
    9. Overall weight: 9.5kg
    10. Bore: 47mm
    11. Stroke: 38mm
    12. Compression ratio: 6:1

    specs of 48 cc


    1. Engine Type: Single cylinder, air-cooled, 2-stroke
    2. Type of fuel mix :(16:1/20:1)
    3. Displacement: 48cc
    4. Ignition: C.D.I. ignition
    5. MAX.Power: 1.2kW @ 5500rpm
    6. Economy: 100 km/1.2 litre fuel
    7. Nominal speed: 30-35km/h
    8. Fuel tank: 2 litre
    9. Overall weight: 9kg
    10. Bore: 40mm
    11. Stroke: 38mm
    12. Compression ratio: 6:1

    :whistling:

    1. Engine Type: Single cylinder, air-cooled, 2-stroke
    2. Type of fuel mix :(16:1/20:1)
    3. Displacement: 48cc
    4. Ignition: C.D.I. ignition
    5. MAX.Power: 1.2kW @ 5500rpm
    6. Economy: 100 km/1.2 litre fuel
    7. Nominal speed: 30-35km/h
    8. Fuel tank: 2 litre
    9. Overall weight: 9kg
    10. Bore: 40mm
    11. Stroke: 38mm
    12. Compression ratio: 6:1
    :tt1::tt1:
    ohhh my 48cc even tho its a rse hp1.5
    topped out at 65 khp with a 44 rear an modded stock exhaust .
    revs felt like 7000 rpm

    now about to add sbp shiftkit.expansion.lo profile air ,metal throttle body ,rocker kill .

    brad
    syd
     
  3. buzbikebklyn1

    buzbikebklyn1 New Member

    So...5500 seems to be the manufacturers limit... good.
    I wasn't far off, better to err on the side of safety with these little hand grenades.
    Thanks.
    BBB
     
  4. buzbikebklyn1

    buzbikebklyn1 New Member

    The shift kits worth every penny, just down load the assembly manual to a lap top and pay close attention as you put it together.
    Most of the holes in the mounting plate, U bolt clamps, and were the engine its self bolts to the mount will need to be elongated and filed out... just work slowly, measure carefully before drilling.

    Chain alignment and tension are crucial to the smooth operation of a shift kit.

    Once you have the engine were you want it make sure your carb and air cleaner and exhaust/exp. pipe all fit well BEFORE drilling and filing!

    I use several different straight edges and rulers for chain alignment, the straighter the chains run the less drag and wear there will be on the system, it will shift easier as well with less inner chain ring jumps.
    Don't forget the jump stop! its very important to save your frame in the event of a major drive chain failure.
    Good luck, thanks for the RPM 411
    BBB
     
  5. HeadSmess

    HeadSmess Well-Known Member

    yeah. 5500. the porting durations/areas restrict it to 7k. so you may get that, but at the cost of reliability...(with these? what?! :p )

    tweaking can alter this, but after getting 80km/h from one, then experiencing an....isssue, im just concerned with power/torque. lugging power. :)

    speeds great. until you stop suddenly :jester:
     
  6. buzbikebklyn1

    buzbikebklyn1 New Member

    Everyone that runs a China girl needs to remember, these things are cast from Chinese beer cans... what can we really expect out of them?
    Look at the Morini... its cast from Italian beer cans, it got less displacement yet puts out 3 times the power with way better longevity...
    Now what we REALLY need is a china doll clone that cast from good old AMERICAN BEER CANS!
    LOOK OUT...
    lol
    BBB
     
  7. yeah. i would love to be able to buy an american made engine. although im sure the price would be much higher. but i think if the price truely reflected the quality. i would have a problem paying more. it just seems that never the case these days.
     
  8. adrian101

    adrian101 Member

    are you really serious that they are built from beer cans? If so i'm building my own from Australian beer cans. LOL
     
  9. When I calculated the top speed and gearing of my bike I think at wide oped throttle the engine would hit about 7500 RPM. I don't normally go that fast though. Doesn't sound healthy at all.
     
  10. wheelbender6

    wheelbender6 Well-Known Member

    These engines let you know when they reach max RPM through sound and feel. There is a point where the engine goes from smooth and happy to vibration and strain. To me, that is a better indication than a tachometer.
     
  11. buzbikebklyn1

    buzbikebklyn1 New Member

    STRUTHE! those big fosters cans should work well.
    BBB
     
  12. headtrama

    headtrama New Member

    I have had mine up to 8200 rpm seemed to smooth out and sound different .
     
  13. jjhackr

    jjhackr Guest

    I lifted the exhaust port on my 48cc and fabricated an expansion chamber tuned for 10500 rpm. Now it screams like a dirt bike. I've been commuting everyday since the modifications and have racked up 6000 miles at red line WOT (I abuse that engine). These engines are solid. all of the problems i have had with the bike were not related to the engine or the modifications i made. I have replaced the rings once but everything else in the engine is the same. so, yeah. Far from hand grenades lol
     
  14. HeadSmess

    HeadSmess Well-Known Member


    yay, another advocate of smaller is better. always liked the 48's. the skyhawk, black with round fins seemed to be the best of the bunch.kept them stock mainly because once you have made a good pipe...its really easy to swap over.

    as for the 66... meh. hard to comment when you only got one and it never was capable of even going 5 minutes without some type of issue. dodgy ebay junk engine, was listed as a 48.
     
  15. Joshest

    Joshest Guest

    45km/h with 56tooth /19inc wheels or 33 sprocket 72km/h its gonna make 9000rpm. carburator drilled 16mm, exhaust without cap and drilled, head -2,5mm and ported silinder 2,4cm wide and exhaus port 2,5mm higher. And you got "Race engine" what lasts about 50hours :D
     
  16. Steve Best

    Steve Best Active Member

    I just did 36 kms at 55 to 66 kph with my Grubee GT5A.
    It starts detonating at max speed and load, screaming for one of Jaguar's ignitions.

    Here is the head before and after a wipe. Oil was a jug of unlabeled semi-synthetic I had on the shelf, 32:1.

    [​IMG]

    [​IMG]

    So how many rpm am I doing with a 44t sprocket and 26" MTB tires at 66 kph?

    Steve
     
  17. Frankfort MB's

    Frankfort MB's Well-Known Member

    That's 41 mph!!! What have you done to your engine. 41 is winding out though I know that, I think I was hitting 7500ish around 37 with a 44tooth
     
  18. FurryOnTheInside

    FurryOnTheInside Active Member

    2.8kph per 100rpm of the output sprocket.
    410rpm = 100rpm at the output sprocket.
    I get confused with direct drive, do this all the time for shift kit ratios, but I think it's 9664 rpm = 66kph (on 10:44, 26")
     
  19. FurryOnTheInside

    FurryOnTheInside Active Member

    8428rpm I think
    If you take 410rpm as 1.8mph on a 10:44 26"
     
  20. Frankfort MB's

    Frankfort MB's Well-Known Member

    That sounds about right, looking back at my old thread about that and i said 34mph. I sense then bought a mzmiamiparts expansion chamber and it must be tuned for 7500 because as soon as i would max out old exhaust, my new exhaust would seem like it let the turbo spool lol she kept climbing and climbing but the very large turn kept getting closer and closer so I had to stop:D
     
    gus. likes this.
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