horse power mods?

Discussion in 'Performance Mods' started by mean lean, Feb 28, 2008.

  1. mean lean

    mean lean Member

    If you havnt seen ultimusmaximus's horse power updrades its worth a look. can anyone tell me if one of those pocket bike carbys would give some gains in performance on its own, or is the pipe and boring needed where its at? the stock carby on my chinese motor is a leaky little thing, not enough reason alone to justify upgrade though.

  2. A properly designed tuned pipe (expansion chamber) would provide the most power increase for the engine....The most economical way to achieve a higher top speed for the bike would be a smaller sprocket in most cases.
    Hope this helps.
  3. ultimusmaximus

    ultimusmaximus New Member

    the key to increased power is letting the engine breathe better... a better carb that delivers air and fuel more efficient is going to compliment a tuned pipe with better exhaust flow...
  4. mean lean

    mean lean Member

    cheers fellas,
    top speeds not my want, more pull and mid range is. need to source somone that can weld a pipe for me. andrew, ill be looking into a larger sprocket some time soon. can you tell me how to find thred on gear ratios, think im running a 44tooth about 40kmph comfortably. thanks again.
  5. HI Mean Lean,

    I'm not too knowledgeable about metric and the KPH but generally speaking, every tooth you loose off a 44T sprocket on a 26" wheel will net you about a 1 MPH increase in speed and vice versa (1 tooth over 44 T you loose 1 MPH top end but gain more pull or torque) (this is with the dax 70 engine...different engines might behave differently because of the possibility of different primary reduction gear ratios and front sprocket sizes).

    I'll be happy to help you with the sprockets....thanks for thinking of me!

  6. Oh Mean Lean...I did post a pic of a closer to production ready tuned pipe on this site....look in the wild in the streets section.
  7. mean lean

    mean lean Member

    hey andy,
    thats a nice looking pipe, im worried id have trouble lining it up with my bike, steel frame mtb, motor sits a lot lower than with my aluminium frame. worth some thought. is there chance of forcefull manipulation? BRUTE mechanics?
  8. Hi Mean Lean,
    Thanks for the comments on the pipe.The pipe has a header length and diameter that is very close to optimal for the system and it is adjustable because of threaded fittings so no manhandling needed to adjust pipe to fit most if not all bikes...Final install doesn't really require welding if the pipes are put together tight enough....I haven't welded on mine except in a couple places (fell bead weld) just for the heck of it and because it is goibg to stay on that bike....All metal is heavy enough that a muffler shop can MIG weld if needed....I had to make it that way because I wanted an adaptable pipe that would fit most if not all bikes and be locally weldable by a muffler shop because I figured most people won't have their own welder...To save me time (unless I can find a co to mass produce but then again there may not be enough demand to warrant mass production) I may offer pipe as a kit that would only require minimal welding.
  9. nKKommando

    nKKommando New Member

    kidney pipe & aftermarket carb

    Expansion pipe from 80cc dirtbike and carb from 1980 yamaha GT-80 make this bike HAUL!! This thing will take off from right out of under me. After running a stock set up w/ ram air intake for awhile (the ram air is a great and easy modification that does add on top end as well as torque = HP) I decided to go all out and the gains are surprising. Its amazing it is the same chinese 80 engine. It is loud and has a mean growl from the exhaust. My advise: find some cheap parts and retrofit!

    Attached Files:

  10. word. IMO fancy velocity stacks and tuned pipes on $180 engines are not the answer to unlocking easy HP. Simple cheap and reliable gains on an equally simple and cheap motor are what I am after.
  11. Dean

    Dean Member

    Here's something GM learned back in the 80's.
    It seems mid range power can be built if you increase the length of the passage between the inlet (air filter) and the cylinder.
    One way they did it, was to design an intake manifold in which the passages crossed from one side to another.
    It was called "TPI", which stood for "Tuned Port Injection".
    If you take both your hands and clasp them together, with your fingers interlocking, you'll have a pretty good illustration of what that manifold looked like.
    Keeping with that train of thought, you might want to discard the stock intake pipe and build your own.
    Saw the flanges off so you can reuse them, and weld them to a longer pipe (or cut the stock pipe in half and weld in a length of pipe that has the same inside diameter as your current one.

    How much longer? I couldn't say. That's going to have to be a trial-and-error thing, unless you can find some kind of mathamatical formula that'll give you the answer (or at least get you in the ball park).

    Also, an overbore kit will build power in the mid range and a little of the upper end.

    I found that out, back when I was messing around with VW Beetles.

    My dad had a european '67 1300 (that had the steering swapped over).

    He found a '68 1500 for me, but the engine came in 3 boxes, so we rebuilt it over the winter.
    Once it was done, he put it in his car (thanks dad! :rolleyes:), because it was time to rebuild his engine.

    Now understand that the difference between the 1300, the 1500 and the 1600 is simply the bore size. Everything else is the same (VW did that on purpose).
    With a 5mm larger bore, he noticed that the car could pass slower vehicles much more quickly.
    When he rebuilt his 1300, he picked up a set of 1600 cylinders and pistons and used those and although it didn't seem to take off any quicker, it didn't lose as much power at highway speeds (90-100kmh) as it did with the smaller stock cylinders.

    Same goes for any engine, even these little buzz bombs, so it might be something to keep in mind, should you ever find yourself with some time and a little extra cash.

  12. fastboy9

    fastboy9 Member

    New chrome exhaust

    Just ordered a new chromed tuned expansion chamber exhaust pipe for my bike. Cant wait for it to arrive! Last pipe literally exploded, the header pipe was left behind so I'm going to weld on to that. This is a design I did on Photoshop with what it is going to look like. If any body has any ideas for a better place to mount the pipe I'd love to hear it. I'll keep you posted on how I did it. Its a pocket bike / mini moto racing pipe which I got off ebay for 99p! the bloke spelt it wrong in the title so nobody could find it!

    Attached Files:

  13. Hi,
    That first bend out of the engine looks really to have a longer smoother radius bend or a pipe that flairs out (the flair out is hard to do without extensive fabbing....straight pipe is easier to use)...Maybe run the header pipe out a bit and wrap it around the the down tube instead of before the down tube.
    Nice job on the photoshop....I need to get high tech like that!
  14. Ghost0

    Ghost0 Guest

  15. Dean

    Dean Member

    Another idea may be to hire the job out to a professional mechanic who has a hydraulic (or pneumatic) tubing bender.
    In the states we have "muffler shops", where most of the work deals with the exhaust system.
    Anyone who's done that for a while can take a tail pipe and bend it into anything they want.
    I just don't know if they'll have the mandrels to work with pipe that small (diameter).
    Heat the pipe with a propane torch and bend it over the closed jaws of a vice.
    Work in "baby steps" and constantly check for "fittage" (my own word ;) ).

    As GhostO and Andyinchville1 pointed out, you want to stay away from tight bends.
    Ideally, you'd want a big round circular bend coming from the flange, up as high as possible, before changing direction at the expansion pipe.
    You also want that change in direction to be as smooth and seamless as possible.
    In the end, the new pipe would be shaped like a question mark.

    Just remember...Big Circles.
    You always want to achieve that when you're shaping the pipe.

  16. fastboy9

    fastboy9 Member

    Brilliant thanks for the advice guys! smooth and seamless... this will be my first time doing anything like this so thanks for your input and I'll get some pics up soon.
  17. Dean

    Dean Member

    You're welcome.
    Look forward to seeing the pics.

  18. spunout

    spunout Member

    i think you all should consider this...

    this is a Keihin PC10c carb off of a XR80. the intake is handmade.
    i wish i could say it was my idea and workmanship, but i have the imagination of a single-celled organism, and two left hands (long story. horrible accident:lol:). anyway, this is how i got the motor, and like i said before, it screams!
    AZvinnie rode it, Spooky's roland and fred both rode it. roland said "thats alot of torque. you could put on a 30tooth sprocket and get away with it."
    and unscrew the baffle from your exhaust can and GET RID of it! the baffle robs power.
    yeah, its not pretty, but who cares?

    ps-notice how the intake doesnt have a sharp bend
    pps-fastboy....its from an XR80.

    Attached Files:

    Last edited: Mar 19, 2008
  19. fastboy9

    fastboy9 Member

    whoa! is it me or is that thing huge! where did you get it?
  20. fastboy9

    fastboy9 Member

    Anybody really serious about tuning the engine may find this pdf very useful. Its a book on every aspect of the two stroke engine.