how do you go about getting in the over 50 mph club.



chuck228

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#2
so far ive ported the cylinder and drilled and smoothed the piston skirt to get more fuel i bought the jack shaft from sick bicycle parts wich has made a big difference gutted out stock muffler but replaced the cap bought the supper roo and the heavy duty magnito . i want to get a better head and muffler. i still have a boost bottle and reed valves im trying to get working on it. i also put a pull start on it. im new at this but its getting in my blood fast. i will post picture just as soon as i clean it up a little. thanks for letting me join i love all the info i can get of what i can and shouldnt do to help me in my quest
 

KCvale

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#7
I cannot quite break 60kph but find my bike plenty fast, especially when it come time to stop.
60kph is only 37mph, he wants to go 60mph, that is 97kph.

I sure hope you have really solid nice bike with dual disc brake and good tires as bicycle parts won't take that kind of speed.

"gutted out stock muffler but replaced the cap
i want to get a better head and muffler.
i still have a boost bottle and reed valves im trying to get working on it."

It really helps to understand how a stoke engine works if you want to improve performance.
It has no valves, it tries to do intake and exhaust at the same time.

First of all throw the 'sucker bottle' away, they don't do anything with a regular system but lighten your wallet, and with an intake reed nothing comes back to catch and 'boost back' anyway.

Next is understanding the exhaust.
You lost power by gutting your exhaust, you want a timed push back to shove the escaping unburnt fuel back into the cylinder.

Just follow the green intake fuel mix path.



An expansion chamber exhaust is like a reverse turbo charger, it shoves that wasted fuel back in for a bigger fuel mix.

Then take page from the rice rockets book, get aerodynamic!
After ~32mph you are just fighting the wind resistance.

Want to actually feel how much force?
Hold you hand out the window in a car at 60mph and turn it.

You can go for more power to compensate, or just make the force less with aerodynamics.
 

HeadSmess

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#8
couldnt have said it better.

tuned exhausts are the be all and end all of two strokes.

your entire list reads like the typical shopping list of bling bits that have great advertising but dont do anything.

look at advertising like this...if someone is paying someone to show you something to make you buy it...what they are showing must be pretty useless. (not always the case but when you get some popup adware trying to redirect you constantly...)
rarely see pipes advertised, or, should i say, NEVER see GOOD pipes advertised... see lots of bling lookalikes that do nothing but have lots of blurb in the ad.

you say ported...but really? what are the new port timings? you did measure them, didnt you? degree wheel and a port map? knew how much and where to remove material?

you need a really good bike. brakes welds wheels geometry. cutting corners here...well... iunno what insurance companies think about motorized bikes that do high speeds... but dont expect a payout.

you need to REALLY understand two strokes, the porting, the breathing, the dynamics.

you need mechanical skills, metal working skills and not to mention, common sense!

be wary that it can and will seize when you least expect it...and that is truly scary at high speed.

a ticking timebomb... youll always be waiting for it to blow up and fail when its worked to the limit.

get a morini/denardis if RELIABLE speed is what you want. they are designed to do what you want. and theres no need to dismantle them!


oh yeah...i just re read and theres a mention of wind resistance... goes up on the square of the speed, dont it?

fairings? just put them all back on my moto and gained 50km a tank...

so now you really want to do some wind tunnel work or most of your fuel to move you at speed goes out the exhaust. very inefficient. you have to make all this unnecessary power.

weight wont affect its top speed(much)...just how long it takes to get there. but wind resistance/power will!

be happy with 30-40 and get a real motorbike for going fast. theyre made for it.
 

bakaneko

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#9
60kph is only 37mph, he wants to go 60mph, that is 97kph.

An expansion chamber exhaust is like a reverse turbo charger, it shoves that wasted fuel back in for a bigger fuel mix.
any suggestions on the best shape for the expansion chamber exhaust? there seems to be many varieties on eBay.
 

butre

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#10
none of the ones advertised for motorized bicycles work, with the possible exception of mzmiami's racing pipe ( http://www.ebay.com/itm/271952212120 ). I haven't tested the thing but it looks like it should work well.

a used CR80 pipe will run you about $60. bring it and a bottle of good whiskey to a local welder and he'll make it fit your bike.
 

sbest

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#11
Most 80cc MX bikes rev over 10,000 rpm, compared to our 8000.
What do you do to get the tune right for our operating rpm?


Steve
 

HeadSmess

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#12
Walter Kaaden, the chief engineer for MZ motorcycles in the 1950s, is generally considered the father of the modern two stroke expansion chamber. He reportedly said "You'll know when you have the design right, because the chamber will then be impossible to fit on the motorcycle without having it drag the ground, burn the rider's leg, or force the relocation of one or more major components."

http://www.dansmc.com/exhaust_2.htm
 

butre

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#13
Most 80cc MX bikes rev over 10,000 rpm, compared to our 8000.
What do you do to get the tune right for our operating rpm?


Steve
either do what I did and increase the operating RPM, or do the smart thing and shorten the header pipe
 

KCvale

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#14
The SickBikeParts.com x-chamber works very well.



That thing would do 40+ even with the fat tires and sitting up and no fancy porting or than the normal intake and exhaust.
NGK plug of course, the SBP pipe and 7-speed shifting.
 
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#15
Gearing and port timing are important. With any 2 stroke and expansion chamber is always better. Oil ratios also matter but i doubt you could get it past 60mph my Kawasaki Kx100 barely with reed valves barley hits 63. I think with the 66cc with all performance parts you'll top out at maybe a ball hair over 50
 
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#16
Wind resistance has a squared relationship to speed. I.e. The resistance at 50 is 4x that at 25. This is where higher hp comes into play. I suggest you look into fabricating some fiberglass fairings and fenders; lower bars etc. I've hit 60 going downhill and man it was downright scary without suspension or anything... Good luck
 

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