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Discussion in 'Bling and Appearance' at netrider.net.au started by spud_90_5, Sep 13, 2006.

  1. hi, I was wondering how i could de-restrcit my aprilia mx 50 because i want a bit more power out of it.

  2. how much do you want to spend?
  3. not sure, why? what where you going to suggest? i thoguht about a sports exhaust.
  4. Power for your buck, sports exaust are over-rated in my opinion.

    A good start but don't expect much more than a change in note.

    Power comes from heads, cams, inlet, exaust, carbys. Play with one and affect the other.
  5. Not on a 2-stroke it doesn't. A good expansion chamber (exhaust) specifically tuned for that engine will make the biggest difference. Then I think a good variator would probably be the next best thing, but I'm sure there are others on Netrider who know a lot more about tuning scooters than I do.
  6. Sorry I didn't realise it was a 2 stroke.They are much more reliant on back pressure.

    increased back pressure gives sronger "posative/negative impulses" in the expansion chamber (lumpy bit in exaust).

    Reduceing back pressure reduces the strengths of the internal impulses so they can't do thier job.

    The internal pulses are basically a shock-wave from the exaust gas, traveling out it's a posative pulse, backwards being negative and this is the entire so called "power band" of 2 strokes.

    As a posative pulse is echoed/amplified in the expansion chamber and bounced back towards the cylinder exaust port, at particular revs the negative pulse bounces back of the cylinder wall at an advantagous time

    If the exaust port opens just after the negative pulse bounces back to become a posative pulse, it in effect scavenges (sucks) the exaust gas out of the cylinder to allow a greater fresher charge.

    Thats all a power band is and if you play with back pressures on 2 strokes, don't expect an improvement instead a change of power curves/chacteristics.

    4 strokes use the same principle but with much less effect on the exaust side.
  7. Sorry but that is just plain wrong. I may not know much about tuning scooters. but I tuned and raced 2-Strokes for many years, from 50cc and 125cc GP bikes many years ago, to RGV 250cc Proddy racers in the 90s. Yes an expansion chamber will shift the HP/torque on the power band, but I have seen overall power increases of as much as 20% on exhaust tuning alone. Bear in mind that the original exhaust has to do things that one tuned purely for power does not, like reduce noise, improve fuel economy, and contribute to emission reduction.
  8. I explained how the expansion works in simple terms, I am correct 100% on an expansion chambers function. Power bands on 2 strokes are soley due to expansion chambers with thier negative/posative pulses.

    I know it's hard to believe but yes, power bands as we know them are 100% from the expansion chamber. They like back pressure to work effectively.

    Nothing else is involved in a power band, changeing expansion chambers changes the engines power curves as mentioned but nothing is free.

    Differently desighned expansion chambers can tend to rob mid range for top end and that sort of thing so yes power increases can come from it but only at the cost of power else where in the rev range.

    The same principle is used in plenums, ram tubes ect. Some are better than others but the general rule is you will rob power else where to gain top end.

    edit~changeing the expansion chamber will go one of two directions.

    1, intensify the impulse to work on a narrower rev range (tuned to a particular rpm, you will lose mid range)

    2, flatten the impulse to work over a broader rev range (no real top end but broader power curves for mid range)

    You could a unit for a massive impulse on mid rpm but no one builds them.

    So what incantiatios said is right, more power can available but it aint free.
  9. this is hilarious... are we answering the guys question or just trying to prove who is the most intelligent?
  10. I tried to give him excess info I know, but an informed choice is better than an ill-informed one.
  11. What's more hilarious is that we're trying to work out how to get more power from a 50cc scooter... i doubt any noticable difference will be achieved - remember its ONLY 50cc in the first place.
  12. lol, thanks for all the imput but all i asked was how t de-ristrict my aprilia mx 50 supermoto? but i dont think any one answered it lol, i may be mistaken.
  13. It has been answered in parts, especially in the earlier posts, like many questions asked here, you may have to sift thru a little to get an answer - or the answer you want :)
  14. I only supplied the info, it's up to you to understand it.
  15. Don't the Aprillas have a "restrictor" somewhere on board that .... restricts the power produced by the engine? Could this be what he wants to get rid of?
  16. yes, that is what i want to get rid of but i dont know how.