Standard Horepower?

Discussion in 'Motorized Bicycle General Discussion' started by copmagnet80cc, May 2, 2014.

  1. copmagnet80cc

    copmagnet80cc New Member

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    Ive got a 80/66 cc engine. Does anyone know the standard horepower these engines get? Or how I can find out how much they have stock
     
  2. Theon

    Theon New Member

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    It seems they vary.
    Around 2 HP.
    Tony from RSE told me he has dyno'ed standard motors and got little over 1200W.
    1500W would be 2HP.
     
  3. copmagnet80cc

    copmagnet80cc New Member

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    Thank ya. I knew it couldnt too much but i wasnt sure exactly where it was at. Ive ported my engine a little bit and got some more compression on it but i doubt it makes too much of a HP difference.
     
  4. mapbike

    mapbike Active Member

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    Getting compression up a bit helps some alright, but most important thing with and engine is getting it to breathe as good as possible, some cleaned up ports and a well tuned carb along with an unrestricted exhaust is key to getting a nice performance boost with these little engines.

    Map
    .wee.
     
  5. Techbiker

    Techbiker New Member

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    Expansion chambers help a ton too! I threw a billet intake and SBP expansion chamber exhaust on my 69cc thatsdax HT and it really opened up top-end power. It wasn't really scientific but I rode up a steep, long hill in the countryside a few times with the expansion chamber and with the stock exhaust at full throttle. Both times I approached the hill at 26 mph.

    With stock exhaust, my speed dropped to 15mph half way up the hill. I had to pedal assist to make it to the top quickly.

    After installing the expansion pipe, my speed dropped to 22mph half way up.

    I gain of 7mph under heavy load was very significant! I was limited to around 26 mph due to engine vibration anyway. The only issue with the SBP expansion chamber was the noise.

    If your expansion chamber is non-adjustable, you may consider lengthening or shortening it to maximize the performance gains where you want them.
     
  6. Theon

    Theon New Member

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    A well designed expansion chamber will give better top end, an off the shelf expansion chamber is more likely to give better low to mid.
    Real HP increase is through revs, HP = torque x revs.
    Increasing compression and cleaning the ports will give better torque, getting the max torque at higher revs is through port timing, with sacrifice to low end torque.
    Getting a well designed pipe that works at desired revs will 'super charge' your motor.
    But again sacrificing low down, and making motor 'peaky' which doesn't suit single speed.
    A 'streetable' motor relies on low to mid range torque, it's hard to have both out of such a small motor.
    Then ignition timing can also play a role.
    But some of these cheaper motors are so far 'out' in port timing, this is one of there biggest 'hold ups' in my experience. A well set up motor even with a 'good' standard pipe, will still get you to 40 MPH.
     
  7. The_Aleman

    The_Aleman New Member

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    That's a bit overgeneralizing. It depends on the expansion chamber. An "off the shelf" exhaust can give more average power than a supposed
    "well-designed" one. 2-stroke power output is really all relative and subjective to the user's needs.

    HP is a number derived from the solution (torque * RPM / 5252). HP is not derived from revs, it is derived from torque at any RPM.

    Torque does the real-world work. An expansion chamber isn't even necessary. High RPM HP often just wears an engine out quicker.
     
  8. sub66

    sub66 New Member

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    out of the box its 1.5 hp
    5/8" hole in stock exhaust tip for me was awesome. felt like 2.5hp and the sound would pick people off their lazyboys to see what they are missing. i even miss it.
     
  9. sub66

    sub66 New Member

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    any changes from stock require a possible rejet of carb. anything. filter. exhaust. gearing too will raise hidden issues that otherwise were ok. just thought i should add warning to previous post/ posts.
     
  10. The_Aleman

    The_Aleman New Member

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    I had a Grubee GT5 (66CC) with a factory badge stuck on it with date of manufacture that claimed it was 2.75HP @ 5x00 RPM (forget the exact RPM it said).

    Might have been about accurate with the stock kit gear it came with. That one had one of the black cat pipes. Seemed to have less power than 2 of the Dax 66 I had.

    From my experience, the power varies widely with the bigger chinagirl engines. You might get a crappy one with lots of gear noise that struggles to rev, you might get an eager, quiet engine that runs easily and revs over 7K. Lots of in-between. There's 5 days in a week and only one of em is a Wednesday lol

    2.5-3.5HP is about the range I'd guesstimate stock. There is no "standard" because build quality varies so much with them.
    IMHO the important thing to consider with the 66 is the torque. They can make great torque without revving high.
     
  11. mapbike

    mapbike Active Member

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    Agreed..

    For a long time now, it has been said on this forum of the China Girl/HT engines " They are a crap shoot "

    I do believe there are some that are coming over now such as the GenIV Dax engines and the GenV (motorbicycleracing) engines which are the same from what I understand, that are better balanced and have better main bearings and lower shimmed con rod bearing, also Fred Chelminski has said that "Silver Jet Engines that Piston bike is selling are very well balanced 38mm stroke engines, he said about the best he has seen out of the box, personally I have two of the Dax GenIV lowers built up and they are really good running engines and the smoothest at high rpms that I have had, 40+ comfortable MPH with both of these engines.

    Power with these two engines is great, I have an older who knows what "brand" with the same basic mods to it as my first GenIV Dax build and the dax engine has a noticeable amount more torque and HP, which honestly I think is due to the much better balance of the GenIV Dax lower, higher smoother revs, when I had my Tach on that bike I logged 9,400 RPM with that engine NOT running an expansion pipe and running a well tuned NT carb at 45+ MPH, torque was lacking a little with that exhaust, and now with a small expansion pipe torque is better but top speed has fallen to the 42-43 MPH which I'm OK with since the lower revs will force me to ride a bit slower and maybe make the engine last a bit longer.

    Yeah I know I said a lot here, but I said all this to say that, the "crap shoot" phrase still applies to the China Girls in regards to what you will have when you get done with one even with mods and good tuning, but there are some engines we have available lately that offer a nice performance increase mainly due to the better bearings and the better balanced cranks some of them are coming with.

    Map
    .wee.
     

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