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Thread: Push most power out of 50cc barrel

  1. #1
    apriliaforum newb
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    Push most power out of 50cc barrel

    Anybody has any tips to squeeze most power from am6 stock cylinder kit?
    Maybe reeds? Different air filters, 17.5mm carb, sports exhaust, what else?

  2. #2
    apriliaforum expert Rj_666's Avatar
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    Really, your only areas to improve power (given the use of a 'stock' cylinder) is intake and exhaust.
    Better reeds, better intake manifold, match the intake manifold to reed valve inlet, and larger carb.
    Stick with the stock airbox.

    Now if by 'stock', you mean only that the bike is 50cc displacement, and not necessarily using the OEM Aprilia supplied cylinder / head... that's a WHOLE different story.

    That said, define 'power'. Do you ride between stop signs, and want acceleration, or do you ride freeways and need top speed ?
    These two ends of the spectrum may be better balanced by changing gearing.

    Remember that it is a SYSTEM, with all parts working together.

    Look over Xero's 'RS Ascension' post... Xero was (at last notice) still running a 50cc cylinder, and has some great thoughts.
    Last edited by Rj_666; 12-05-2017 at 12:39 AM.

  3. #3
    apriliaforum expert ToraTora's Avatar
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    The Study

    Depends on your objectives. Are you trying to build a race bike? Street bike? Drag bike? The stock cylinder could be reworked, although usually what people do is replace the top end with one designed for their intended purpose. There are actually a decent number of performance 50cc top ends available for the AM6.

    Because the stock cylinder has relatively mild port timings you could modify them with a decent amount of improved expectations. You could also enlarge the transfer getting more fuel into the chamber. There are actually quite a few techniques that could be applied. If you are just starting out though expect to do some learning the hard way by messing up more than a few cylinders. This is why most folks just buy a top end designed for the purpose.

    There are two books that are regarded as the best starting point for learning these arts. These are probably the best places to start with the learning.

    https://www.amazon.com/Two-Stroke-Pe.../dp/1859606199

    https://www.amazon.com/Two-stroke-Tu.../dp/0912656417

    That actually answers the question asked. But your real question is probably how to make your bike a bit faster. For that you are probably best off with getting some sort of Big Bore Kit (BBK), a larger carb, a pipe, and the other usual items that people get for their bikes when they want more power. These are by far much easier ways of achieving those desires than hand tuning. For sure the study is probably more life enriching, but the effort required is usually enough to deter most people.

    Still, tuning is a beautiful rabbit hole.

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    Well actually main goal is to get more power, but still have good fuel economy bike

  5. #5
    apriliaforum Member Satanic's Avatar
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    50cc was designed for propelling lightweight children on lightweight minibikes. Very insufficient for propelling grown adults on adult size bikes.



    Most effective way to gain more power, while maintaining fuel economy is: larger capacity engine block.



    Airsal H01138248 (Iron 70cc)

    Smear a thin layer of semi-hardening gasket compound on its metal base gasket.



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    apriliaforum expert Spudgun60's Avatar
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    Isn't there an expression that runs: There's no substitute for cubes?
    Gone, but not forgotten. 1999 RS50.


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    Ok, how about top racing crank, skf c4 bearings, airsal sport 80cc cylinder?

  8. #8
    apriliaforum Member Satanic's Avatar
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    80cc aluminium vibration is harsh on engine mounting lugs. 70cc Iron absorbs vibration better.


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    But am6 engine has balancing shaft, btw how is my brake bleeding method, Satanic?

  10. #10
    apriliaforum expert ToraTora's Avatar
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    Quote Originally Posted by Satanic View Post
    50cc was designed for propelling lightweight children on lightweight minibikes. Very insufficient for propelling grown adults on adult size bikes.
    Depends on the bike, how's its tuned, and its purpose.

    In the 60's when the Ultra-light weight bikes were still racing competitively at the Isle of Man the 50cc bikes were averaging in the 80mph zone. When you consider that the 100mph figure had only recently been reached in '57 with a much larger four cylinder Gilera that's damn impressive that the 50cc bikes were within ~15mph average of the fastest guys recently preceding them.


    Quote Originally Posted by Satanic View Post
    80cc aluminium vibration is harsh on engine mounting lugs. 70cc Iron absorbs vibration better.
    Yeah I'm not buying that argument. A badly balanced system is badly balanced.

    Quote Originally Posted by Gvidas View Post
    But am6 engine has balancing shaft, btw how is my brake bleeding method, Satanic?
    They do, and so does the Derbi engine in the GPRs/RS4s. The dirt bike style bikes however do not. Still the balancer is set to offset the weight of the stock 50cc piston. For it to remain in balance either the replacement piston needs to be very close to that weight, or the crank shaft has to be designed to work with the heavier piston. It would be possible to add mass to the balance shaft, but I don't know of anyone that's played around with that solution yet.

    Quote Originally Posted by Gvidas View Post
    Ok, how about top racing crank, skf c4 bearings, airsal sport 80cc cylinder?
    This question leads back to your intent for the bike. There are plenty of reasons to go through the whole engine, and do a proper performance build.

    Quote Originally Posted by Gvidas View Post
    Well actually main goal is to get more power, but still have good fuel economy bike
    Does where you live have any crazy laws prohibiting you from going to a larger top end? If not that's going to be the easiest way to achieve your desired results. If you put a larger top end on, and keep the carburetor small enough you can get more power, especially in the lower RPMs, and not use a whole lot more fuel.

  11. #11
    apriliaforum expert ToraTora's Avatar
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    Quote Originally Posted by Spudgun60 View Post
    Isn't there an expression that runs: There's no substitute for cubes?
    "There's no replacement for displacement."

    But there is, and it's called super charging. Expansion chambers are a form of super charging.

  12. #12
    apriliaforum Member Satanic's Avatar
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    Quote Originally Posted by ToraTora View Post
    Yeah I'm not buying that argument. A badly balanced system is badly balanced.
    And I don't continue buying into marketing hype.

    Click image for larger version. 

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    £69 Jasil crank vibrates no more than the £130 Doppler endurance.

    Malossi only manufacture one 325 euro crankshaft for both 50cc and 80cc pistons.
    Last edited by Satanic; 12-05-2017 at 10:22 PM.

  13. #13
    apriliaforum expert mattology's Avatar
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    the modulus of cast iron actually does absorb vibrations much much better than steel. it's interesting for sure. look it up in a materials book sometime math and science master
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  14. #14
    apriliaforum expert ToraTora's Avatar
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    Quote Originally Posted by mattology View Post
    the modulus of cast iron actually does absorb vibrations much much better than steel. it's interesting for sure. look it up in a materials book sometime math and science master
    Lolz you are always so quick to say things like this with your implied insult. Read what I said. I'm not debating that one material can absorb more than another, I'm saying that's not the solution to a badly balance system.

  15. #15
    apriliaforum expert ToraTora's Avatar
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    Quote Originally Posted by Satanic View Post
    £69 Jasil crank vibrates no more than the £130 Doppler endurance.

    Malossi only manufacture one 325 euro crankshaft for both 50cc and 80cc pistons.
    If you aren't matching the top end to the bottom end, how can you expect proper results? In Malossi's case have you weighed the pistons? I haven't used their cranks, or cylinders so I couldn't say if the crank is designed for all of their kits, or not. You could try asking one of their techs.

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