Need opinions on my possible build.

Discussion in '2-Stroke Engines' started by JohnDN, Apr 10, 2009.

  1. JohnDN

    JohnDN New Member

    I’ve been looking into buying a 66cc bicycle engine kit off of Ebay from Boy Go Fast and I can’t decide weither to go for it or not. I got a few specs from the seller:

    Model : Z2-80
    Power * Rotary Speed
    Rated Power : (2.5HP/5000r/min)
    Max. Power : (5-6HP/6000r/min)
    Ignition Mode : CDI
    Compression Ratio :6 : 01
    Driving Ratio :18 : 01
    Fuel type : No. 90
    Mixing Ratio for Fuel and Oil: 16:1 for break period (first 300 miles) 25-30:1 after
    Fuel Consumption :120-170 MPG
    Clutch Type : Friction Plate / Dry
    Speed Limitation :25-40MPH

    10T front sprocket
    44T rear sprocket
    #415/#50 Chain

    It says speeds up to 40MPH, but with 18:1 drive at 5000rpms and 24 inch wheels that’s only 20MPH, and at 6000rpms that’s only 24MPH. I’m not missing something am I? 10T front sprocket and 44T rear, that’s a 4.4:1 ratio, so the engine must be geared down to at least 4.09:1 if it’s a final drive ratio of 18:1. I’d like to have speeds of at least 50MPH. I’m 155 pounds, and if I recall my bike is only around 20 some pounds.
    I’d prefer peak power to be around 5000rpms at 50MPH.

    Some of the mods I was planning I doing were raising the compression ratio (CR) to 9:1. I have access to 100LL avgas in my area if I had to mix some with regular gas.

    I’d use a NGK B6HS spark plug and either stick with the stock spark plug wires or make some solid-copper core wires out of some RG6 quad-shielded coax. I’d like to advance the timing for the increase CR but I don’t know how to do that on these little engines.

    I’d install a reed valve, I can’t find any reasonably priced ones for a 66cc, would a 49cc reed valve (click here) work on a 66cc engine if I made an adapter?

    I’d either purchase a expansion chamber or attempt to make my own using one of the online calculators.

    As for the intake, I was using this calculator to try to find the optimum length at 5000rpms. However this calculator is for a 4-stroke engine, would I have to divide the results by 2 to get a accurate number or is it a completely different formula for two strokes? And I'd most likely use a Amsoil CrankCase Breather Filter (the blue ones), high flow and one of the best filtering filters on the market.

    Finally a few aeromods made with coroplast and inspired by the AeroCivic .
    Last edited: Apr 10, 2009

  2. Mountainman

    Mountainman Active Member

    have heard a few things around here regarding BoyGoFast

    maybe not so fast ?? or two fast ??

    you may wish to look into them a little more ??

    vendor section checked ??

    ride the motor bike THING

    added -- just went to the vendor review section
    looks only like a so so so for the Boygogogo
    Last edited: Apr 10, 2009
  3. fetor56

    fetor56 Guest

    BGF. :ack2:
  4. azbill

    azbill Active Member

    pick a better vendor
  5. JohnDN

    JohnDN New Member

    Alright thanks guys. I looked into a few other sellers on Ebay. I can get a PowerKing engine for $10 more and its rated at 3HP/5000rpms rather than 2.5HP. I'll do a search for that vendor and see some reviews on that engine.

    What about my planned modifications though? Do you think they'd be worthwhile? I'm looking for decent performance, but I'm mainly trying to maximize my gas mileage.
  6. Mountainman

    Mountainman Active Member

    that would be cool -- looking forward to seeing your build

    good luck

    have fun as you build and then ride that motor bike thing
  7. arceeguy

    arceeguy Active Member

    I wouldn't pay attention to any HP ratings you see regarding these engines.

    Before you mod anything, first get the engine set up and running nicely with the stock parts. You might determine that this is too "crude" of an engine to try to "hotrod". You'll get great economy cruising at 20mph with no mods at all.
  8. JohnDN

    JohnDN New Member

    Yea, I planned to break the engine in with stock parts and then start modding once I was sure there were no problems. I live out in the country so at 20mph a trip to town might be too slow for my patience. I'd like a bare minimum of 40mph. As for no modding, the first forum I was involved in was and I guess I've developed a habit from being over there- never settle, keep trying to improve.
  9. fetor56

    fetor56 Guest

    Don't get obsessed with specs or trying to find the absolute cheapest price.These kits vary widely in quality & generally speaking the more u pay the better.Also when u get a kit make sure there are plenty of spare parts cos internal engine parts between vendors are rarely interchangeable.
  10. JohnDN

    JohnDN New Member

    Thanks for the suggestions fetor56, I wasn't aware most parts aren't interchangeable. So I'm looking into all this stuff more before I finally make a purchase. And I think I found a reasonably priced expansion chamber, the one from Sick Bike Parts just added yesterday *thumbs up*.
  11. fetor56

    fetor56 Guest

    SBP's...pretty safe bet i reckon........hold-off for a few days & ppl will be posting reviews about them.