boost bottles, the truth
Sorry if there was a post like this in advance...could not find one!
I have been doing some studying up on boost bottles also known as a juice box and here is the info I have found out...
I also wish to kill a couple myths at the same time too....
I will be blunt...Boost bottles that you buy from Chinese stores and the like are pretty much crap... sorry, but unless you get lucky and tuned them right even then if you do they won't help that much as the design is poor to start off.
myth #1 The principal of a boost bottle will never work.
Answer: Wrong! the principal is there but it is like a expansions chamber in the sense if it isn't made just right and tuned for that specific engine it won't work very well. (That rules out almost all of the boost bottles for sale...sorry!)
Question #2 Who developed the principal?
Answer: Actually a guy at Yamaha's engine devoloment center came up with the idea... and subsequently it is also used on some modern dirt bikes.
Myth #3 If you got reeds you don't need a boost bottle.
Answer: Wrong! When gas/air mix starts to get sucked into the cylinder the whole volume of gas and air get what can be considered relative inertia. Then when the cylinder goes by or the reeds shut or the rotary valve closes the gas/air mix has no where to go causing a high pressure area at the end of the intake. With no where to go but from hence it came so it tries to go back out that way. About the same time at which the gas/air mix starts to turn around the engines tries to suck it in and as you expect it don't work all that well when the fuel/air is going the wrong way. No matter if you have reeds or a rotary intake or nothing of the sort the principal of the boost bottle will work regardless of intake type!
myth #4 The size of the bottle should be the same as the displacement of the engine.
answer: Almost true...The bottle and the hose together should have the same volume as the cylinder. (you must factor in hose volume)
Myth #5... 1/4 in. hose and the like is the right size.
Answer: wrong it's like breathing through a straw with a hose that size compared to such a big volume to fill and drain. The correct size is the same as the carburetor's barrel size. (ex. 12mm Puch moped carb so the hose/pipe to the bottle needs to be of 12mm's too)
Any questions about myth #5 or any of them fell free to ask.
To sum it up the principal boost bottles works really well when made the correct way. To make a effective one the pipe to the bottle must be the same size as the carb and the volume of the bottle and the pipe/hose should be of the same volume as the cylinder. Boost bottles will work the same on any form of intake including rotary and reeds.
This info means you would half to custom make one and you would most likely weld in a pipe of the same size as the carb as hose that size would most like cause many problems. And after thats done it all needs to be same same volume as the cylinder for it to work right.
Custom making one will rule this out of the project book for most of the motorized bicycle guys and gals but for those who try it... Don't let anyone talk you out of it!
Any questions or more in depth explanations wanted feel free to ask I will try to explain it and or answer the question to the best of my ability.