allen
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Please advise benefits if any ,reed valves fitted to 50cc 2 stroke... They are already fitted to this motor,(from China) Thanks in advance for any information, Allen
Reed Valves
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Deleted member 12676
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more power, wider powerband
allen
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Thank you,Allen
Steve Best
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Jag, you should say POTENTIALLY more power and broader powerband.
Sleds and motocross bikes stayed reedless until the early 80s because more power was available without the intake restriction.
Advances in reed technology helped change this but it was really the broader powerband and smooth strong idle that advanced the reed valve.
A small reed on a stock China Girl will typically reduce power somewhat, due to the intake restriction.
The piston needs to have a window drilled in its skirt. Its placement still makes a difference.
Sleds and motocross bikes stayed reedless until the early 80s because more power was available without the intake restriction.
Advances in reed technology helped change this but it was really the broader powerband and smooth strong idle that advanced the reed valve.
A small reed on a stock China Girl will typically reduce power somewhat, due to the intake restriction.
The piston needs to have a window drilled in its skirt. Its placement still makes a difference.
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Deleted member 12676
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OK lets talk specifics.
a piston port intake has a narrow powerband (of best power) that can be made at high RPM such as what motocross bikes use. So a motocross bike can be decent without a reed valve. A reed valve gives better power below that optimum powerband and if properly designed does not give less power than without it. There are occasions when racing that you fall out of the powerband and lug the engine a bit. In those situations the reed valve gives the advantage which is why all MX bikes now have them.
It doesn't matter that they create a flow restriction because the intake duration is 180 degrees, versus the 120 degrees of piston port (of which only 60 degrees is pure intake if it weren't for the inertia of the intake charge).
a piston port intake has a narrow powerband (of best power) that can be made at high RPM such as what motocross bikes use. So a motocross bike can be decent without a reed valve. A reed valve gives better power below that optimum powerband and if properly designed does not give less power than without it. There are occasions when racing that you fall out of the powerband and lug the engine a bit. In those situations the reed valve gives the advantage which is why all MX bikes now have them.
It doesn't matter that they create a flow restriction because the intake duration is 180 degrees, versus the 120 degrees of piston port (of which only 60 degrees is pure intake if it weren't for the inertia of the intake charge).
Can anyone point me to a picture of a china girl piston with the window already cut or some good instructions of what to cut out and where? I'm looking to go reed soon (RSE Kit) as I want that low and mid range and have no issues adding the third transfer port (even have a backup cylinder if worst comes to worst) but haven't spotted a detailed post about where/what to do with the piston window. Thanks boys
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Deleted member 12676
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Perfect, thanks again Jag!
EDIT: On holes to be drilled, there isn't quite room to make a 4 tiered stack of holes if I follow your earlier advice on no less than 10mm from center to center. Does this not apply to this situation? Would it be fine to simply cut out a squarish hole down the length the intake side of the piston to achieve the same affect?
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Deleted member 12676
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yes you can cut a square hole but having many small round holes gives more structural integrity which is why I did it that way.
Would it comprimise the structure to much with a square inlet? What about 3 thin rectangular holes with maybe 3-5 mm inbetween them? Probably just going to have to test it and let you guys know haha.
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