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



chuck228

New Member
Joined
Dec 14, 2015
Messages
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

Motorized Bicycle Vendor
Joined
Apr 18, 2010
Messages
3,518
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

Well-Known Member
Joined
May 17, 2010
Messages
3,007
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

Well-Known Member
Joined
Nov 16, 2015
Messages
1,243
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

Well-Known Member
Joined
Dec 2, 2013
Messages
2,502
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.
 
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