how much compression can these things take?

Discussion in 'Motorized Bicycle General Discussion' started by nolan_speed, Jun 2, 2010.

  1. nolan_speed

    nolan_speed New Member

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    I was looking at removing the cylinder base gasket and installing a thinner head gasket to gain some compression on my 68cc motor but I don't know if the engine is strong enough to take the added power. Anyone have any experience with upping the compression on these things?
    .duh.
     
  2. Fabian

    Fabian New Member

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    Lets not forget that these engines are cheap Chinese garbage; designed on the cheap, manufactured on the cheap and sold to a target market that are prepared to pay for unreliability that's built into a dirt cheap price tag.

    The standard engine is built with only just enough reliability to get you to your destination and from that point it's only hope, luck and prayers that will get you home again.
    Increasing the engine compression ratio will add a bit more stress and consternation making the decision to try for an arrival time 3 hours short of your ETA.

    There are others in this forum which may be able to give an alternative view with regards to increasing engine compression and performance modification; some achieving moderate success.
    My opinion: leave the engine completely standard to preserve what little reliabilty they have.

    I need to add a disclaimer on my words: please don't place any weight on what is written, nor act on any opinion expressed by the author as i've been listed as giving downright lousy and uneducated advise that's not wanted or needed.

    Fabian
     
  3. nolan_speed

    nolan_speed New Member

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    That's exactly what I was thinking Fabian, but I was wondering if anyone has had any luck with hopping these things up and having them last.
     
  4. Fabian

    Fabian New Member

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    The usual tricks apply as to any 2-stroke engine.
    I think it will help going to 8mm head studs if you intend to machine the top of the cylinder and the cylinder head.

    In reality, these engines are underpowered for their capacity, quite possibly to deliberately keep them under 2 horsepower.
    The biggest issue seems to be the factory balancing of the crankshaft, not to mention it's inadequate design, and from there, the intake and exhaust side of things.

    I know the company Puch makes a lot of good parts and the 50cc cylinder almost fits straight onto the cases, with some modification.

    Fabian
     
    #4 Fabian, Jun 2, 2010
    Last edited: Jun 2, 2010
  5. Fabian

    Fabian New Member

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    #5 Fabian, Jun 2, 2010
    Last edited: Jun 2, 2010
  6. nolan_speed

    nolan_speed New Member

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    Is there much of a difference in power/ reliability between the "slant head" motor and the one with the plug sticking straight up? mine has the slant head and I'm thinking about getting another one and was wondering if I should get another slant or try the other one?
     
  7. Ilikeabikea

    Ilikeabikea Moderator
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    I have no base gasket and a real thin head gasket. It hasn't given me any trouble and sure made it run faster.

    I don't think they are junk engines. Mine has proved very reliable. I'm sure there is an occasional bad engine. But for the price they are worth what you pay for them...............
     
  8. Fabian

    Fabian New Member

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    As far as i understand, the main fuction of the slant head is to allow the engine to fit into the more space restricted designes of modern bicycle frames.
    A side affect of this design is to have a cylinder head with reduced volume and thereby increasing the compression ratio over the conventional cylinder head. Some people report gaining power when switching from the straight plug to the angled plug design.

    As a purist, i prefer the straight plug cylinder head with it's vertical and centrally located sparkplug design.

    I've experimented with the Rock Solid Billet Cylinder Head (of which has very high compression) yet wasn't able to get it to work. In the end reverting back to the standard head.
    Having said that, other people have reported tremendous success with the billet cylinder head.

    Fabian
     
    #8 Fabian, Jun 2, 2010
    Last edited: Jun 2, 2010
  9. Kevlarr

    Kevlarr New Member

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    Me either. The biggest problem is people think there's some magic tweak you can do to these motors to turn them into a Hayabusa or something. Another thing is you can't just do one thing and expect great performance gains. Sure there's a few things like porting and adding an expansion pipe that can help quite a bit but turning one of these into a screamer takes quite a bit of work that in my opinion, other then bragging rights, really isn't worth it.

    You wouldn't put a 6-71 blower on a stock Chevy smallblock, oh sure it'll be impressive for a couple of minutes. laff
     
  10. nolan_speed

    nolan_speed New Member

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    Well, you wouldn't put a blower on a small block Chevy but you could shave the heads, port them, install a better cam, intake and carb and pretty soon you don't have a stock small block anymore. With a stock small block V8 (Chevy, Ford, Dodge, etc) the stock bottom ends can take a fair bit of souping up without any problems, sure a supercharger is pushing it but most of the other mods I mentioned aren't. That's kind of what I'm asking here, can they take that kind of souping up or are the bottom ends too weak to handle any added power?
     
  11. Ilikeabikea

    Ilikeabikea Moderator
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    I'm running a really thin head gasket and no base gasket. Tuned intake and exhaust. It runs alot better than stock and has held up real well. Will the bottom end hold up? In my case the answer is yes. If you make a few mods and ride sensibly it won't hurt it a bit. If you make a few mods and run the dog carp out of it it probably won't last. Mine will rev a lot higher rpm after the tweeking. I think it would be easy to over rev if I wasn't careful..........
     
  12. BarelyAWake

    BarelyAWake New Member

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    Slightly higher compression, port matching, tuned exhaust - I think of these more as bringing the thing closer to spec than "souping up" really. A better running engine does last longer ...but the better it runs the harder ya ride it lol

    dnut
     
  13. Fabian

    Fabian New Member

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    Short story on Kevlarr's theme: You wouldn't put a 6-71 blower on a stock Chevy smallblock, oh sure it'll be impressive for a couple of minutes.

    Every January in the city of Canberra (Australia) an exhibition is held celebrating horsepower and the notion of making more of it than anyone else.
    We Australians put Americans to shame when it comes to high horsepower "burnout competitions" and dyno competitions.

    Some years ago i was up there and an entrant in the burnout competition has a modified 400 Chev with an 8/71 blower on the thing.
    In qualifing he blew the engine, giving it his all with the right foot.
    To continue on, he managed to get a standard 350 Chev short block from the local wreckers. In haste, he and his mates swapped over all the high performance parts from the race engine onto the stock short block, including 8/71 blower.

    Well, the result was somewhat spectacular.
    Car is lined up on the burnout staging area and off he goes,,,,,,,,,, for all of about 1.5 seconds, then BOOM, the bottom end comes flying out from beneath the car; rods, pistons, crank and i'm sure the water jackets too!

    Most impressive to watch.
    Here is an example of how we Australians do things.

    YouTube - Summernats Finals 2010 Matt Power.flv

    and some fire

    http://www.youtube.com/watch?v=63TllkYksbI


    Fabian
     
    #13 Fabian, Jun 2, 2010
    Last edited: Jun 2, 2010
  14. Kevlarr

    Kevlarr New Member

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    Reminds me of a poster my brother had when I was a kid, it showed an old straight axle drag car from the early 60's leaving the line with the front wheels in the air, the crank on the ground with all 8 rods and pistons still connected and pointing up.
     
  15. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    Usually we yanks blow stuff up with gunpowder, not gasoline. Cheaper, and makes more smoke.
     
  16. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    If you just want to make a bunch of noise and scare the neighbors (even if they ARE 3 miles away), just fill a garbage bag with oxygen, and then add two balloons full of aceteline, and use a cigarette fuse. Watch the windows dissappear, and the Mrs. have a fit....
     
  17. Goat Herder

    Goat Herder Gutter Rider

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    Boy howdy plug your ears!
     
  18. mapbike

    mapbike Active Member

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    I dont want to offend anyone here but those burnout videos dont impress at all, Where I come from that is called all show and no go, heck I can burn the tires off of an old datsun stationwagon that has an old 4 banger in it and as for the engines in those cars on the videos, I'll bet they were made right here in the good ole USA where we created the HOT ROD and the high horsepower high U-Joint busting torque that can be easily gotten from a big block V8 Chevy, Ford or Dodge no way does anyone do Horsepower better than the American Hot Rodders, never have I seena Nitro Methane Top fuel Dragster with n Australian designed big block engine, all these engines are based on American design and these are the fastest cars on the planet. we do it bestand always have, just like just about everything else, thats what makes us American, we had a better idea and we proved it, being a proud American I had to say all this, not meant to offend in any way, I like Australia and have had friends who lived there and loved the place, I would love to go there myself some day, but in my opinion American HP is best.

    :) Sincerely, Shan

    .flg. usflg
     
  19. Fabian

    Fabian New Member

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    Hi mapbike,

    Please read my below disclaimer - you have not caused any offence, but you mentioned: never have I seena Nitro Methane Top fuel Dragster with n Australian designed big block engine: try this link: http://www.teamsainty.com.au/about-top-fuel-team-sainty/

    Jim Read said that if this engine was in a top US team, it would be taking out records. He also commented on the hemi replicas currently used in top fuel as bandaid engines compared to the Sainty engine, with it's 3 valve overhead cam design, which naturally has been banned from competing in America, for obvious reasons.




    ...........l
    ...........l
    ...........l
    .......\..l../
    .........\l/
     
    #19 Fabian, Jun 2, 2010
    Last edited: Jun 2, 2010
  20. mapbike

    mapbike Active Member

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    That is great Fabian......and I'm glad there is no offense taken because there is no meaness of any kind intended by my post, I can tell by your disclaimer that you have a great since of humor so that tells me you gotta be a great ole fell-ur. I say things sometimes that may seem a little straight from the shoulder and a little crude at times but I truly mean no harm to anyone for any reason, I just have very strong opinions about the things I believe in and dont mind letting the world know, this kinda thinking is what has built the greatest capitolist self governed nations in the world. I love my Country as I know you do yours and people like us dont mind making that fact known...
    God bless, Shan
     

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