ORIGINAL: Tumtuk
i see this is an old thread but came across a good forum thread on these things, below is the quote from a dirt bike tech:
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You guys do not fully understand how and why they work.
#1 yes they do work and they work well depending on how they are designed and if one is even needed.
#2 Boost bottles do NOT add HP or speed
#3 Boost bottle will not compensate for poor jetting.
All a boost bottle will do is help eliminate flat spots in fast open and closed throttle acceleration and deceleration. THAT'S IT!
Not all carbs/intakes have this problem witch is why you only see boost bottles on some bikes, ATV and sleds and even auto.
You can't just install a boost bottle on any bike and have it make any noticeable difference or any difference for that matter.
Placement, displacement, hose sizes and routing makes a big difference.
How they work is simple, When the throttle is quickly slammed shut the rushing intake mixture is bleed off into the boost bottle where it is stored momentarily, when the throttle is opened again the mixture is injected into the intake and act sort of like an accelerator pump on a 4 stroke carb to help eliminate any flat spots. With better and better carbs being made all the time there are less need for boost bottles.
The only time a boost bottle MAY help is if your running say a flat slide 34mm carb on a ported blaster and you are racing where there is rapid on and off the throttle action.
The YZ490 is a good example of why a boost bottle is needed. Capped off the bike would run fine with not problems unless you were riding in the tight tech trails and then the bike had a very noticeable hesitation at 1/4 throttle with rapid throttle action. The STOCK boost bottle was used to eliminate this problem.
Other then that don't waist your $$$ you better of spending it on a 6 pedal reed set up or a 250R style air box set up. You will never feel any full throttle gain or even see a HP gain on dyno.
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Now bringing this over to the RC gas world....if your buggy or truck has flat spots..it may help but wont make it more powerful as the manufacturers claim.
Coming form a long automotive tech background I can agree with his statements. It WILL NOT have any ''supercharging'' effect. All it will do is ''store'' reversion pulses when the throttle is closed abruptly and feed them back to the carb when the throttle is opened again (cleaning up flat spots from reversion). This is not supercharging in any form.
Also the need to closely match the displacement of the bottle(s) to the engine is something I do not think the manufacturers are following closely enough to really make them work...they do look pretty I guess
I think they can be beneficial in the right application but I do not believe any of the manufacturers claims of power improvements. If you have flat spots, try and figure out what is causing them...it usually isn't reversion, most of the small 2 strokes built today handle reversion well enough (although they do tend to idle roughly). They may or may not smooth idle quality I haven't used one to check myself.