Boost Bottles- How to analyze and design them

Discussion in 'Performance Mods' started by jaguar, Sep 3, 2016.

  1. jaguar

    jaguar Well-Known Member

    First off, ignore what people say about them. Other than the motorcycle engineers everybody has been fumbling about blindly.
    Go to the source, the patent which gives all the engineering ideas behind the design. I did and found out that seemingly I’m the only person on the planet willing to pay $26 to know the truth about them because what it reveals shows that no one goes by their tests which proved the best way to design them. It turns out that no one knows any of the engineering principles and manufacturers have just made items of convenience and fashion. No wonder most opinions of boost bottles are negative. People don’t know the operating principles under which they are effective. Most of them are badly designed with tubes too long and too skinny. The very first step in designing one is to make sure the cross sectional area of the tubing is equal to 30% of the area of the carb size. (example: area of 14mm carb is 154 sqr mm. 30% of that is 46 sqr mm which is had with a 7.7mm dia tubing which is almost 5/16") From there the length of the tubing and the volume of the bottle determine the RPM at which it is most effective. The bottles are NOT to be sized in relation to the size of the engine other than not letting them be less than 80% the size of the engine. Most common is 2 to 3 times the size of the engine but the only two things important is the tubing diameter and the resonant RPM.
    I’ve ordered tubing and connectors to make one for my AX100 Suzuki (street bike) since the systems main function is to improve power at partial throttle at lower RPM, which mostly is the case with trail and street bikes. To read my write-up on the topic go to
    Warning: If you do not roll-on the throttle but rather treat it like a light switch then you will only see minor benefit from a boost bottle since it works best during partial throttle when the vacuum/pressure pulses are strong enough to make it fully effective. At full throttle its boost is only about 5%. Do you think you can feel 5% difference in a 2 hp engine? .05 x 2 = .1hp
    Last edited: Sep 6, 2016
    Steve Best likes this.

  2. jaguar

    jaguar Well-Known Member

  3. jaguar

    jaguar Well-Known Member

    I came up with a test to see how accurate my boost bottle calculator is by “feeling” the resonant range of a test bottle. I used a big plastic vitamin bottle and cut the end off it and used a hose clamp to tap it with motorcycle inner tube. I exposed the entrance to the tubing real close to the cone of my computer speaker and then ran a frequency sweep generator on my computer to drive the speaker. I connected my DVM to the speaker to display the changing frequency. With my finger on it I could feel the volume inside the bottle changing as the rubber end was vibrating. The volume only changes while it is reverberating. Surprisingly the band of resonance was right at 2000 RPM wide just like the Yamaha patent showed. Also the center of that band agreed with the resonant RPM that my calculator showed.
    The air humidity when I did the test was 77% and the temperature was 76 degrees Farenheit. For those two the speed of sound in air is 348. 100% humidity (like is in the fuel/air mixture) only increases the speed of sound .2m/s more.
    So I'm pretty content with how the calculator is now. Next step is putting one on my bike and testing the results. I'm designing one so that it works right at the RPM range right below the pipe powerband when there's a power dip.
    Last edited: Sep 25, 2016
  4. Boost bottle

    Boost bottle Guest

    Hi Jaguar,

    I want to try a boost bottle, but I already have an extended intake. I'm guessing that the dampening effect of the extended intake is basically close to what is going on with the boost bottle. I wonder how much more improvement I could attain if I find the right dimensions for a boost bottle/hose setup and I'm wondering just how far off it will be from what your calculator says. I wonder how I could mitigate the mal-parameters that my extended intake presents in this equation. My extended intake is a little less than 5 inches from the reed box to the carb slide and I need it to be able to mount the engine in my small frame. I think all engines with reeds probably have a few inches from the carb slide to the reed setup. Maybe wider and shorter tubing and a smaller bottle volume?

    Best Regards,
  5. jaguar

    jaguar Well-Known Member

    It should help any way. Just have the outlet to the connecting hose as close as possible to the reeds.
    First thing to do is to know the RPM at which your expansion chamber starts giving the engine a boost. That is because for about 1500 RPM below that the engine experiences a lag in power. In that under powered RPM range is where you want the boost bottles action. Design it for a resonant RPM around 800 RPM below where the engine starts to get on the pipe.
  6. jaguar

    jaguar Well-Known Member

    Well I tested with and without the boost bottle on my Suzuki AX100 (2 stroke, reed valve, expansion chamber) and found that it works just like the Yamaha people said it does.

    boost bottle tuned to 4800 RPM (3800-5800 BB powerband) although I wanted it tuned to 5100 but couldn't due to space restrictions.
    increased pilot jet from .6mm to .64mm hole diameter (I drill my jets instead of buying new ones)
    lowered slide cutaway 1mm with JBWeld
    AX100 gets “on the pipe” at 5900 RPM
    Test area: short uphill with a light pole at the bottom of it and one near the top of it. Cruising at 50kph (4800RPM) till first pole and then opening the throttle.
    before boost bottle: no acceleration from 4800 RPM going uphill
    with boost bottle: acceleration from 4800 to 5900 RPM going uphill
  7. jaguar

    jaguar Well-Known Member

    The boost bottle has some usefulness on a standard china girl engine although it is a design made for engines with reed valve and expansion chamber.
    That is because the taper on the needle of the NT carb is too steep which means if you set the needle to its lowest position it will be good for partial throttle power but not so good for open throttle. With a boost bottle (with a 5/16" tubing inner diameter) it leans out the too-rich partial throttle condition without affecting open throttle power. That is because it absorbs some of the vacuum spike that the carb gets each time the intake port is opened. That spike normally causes a spurt of gasoline to come up thru the needle jet which enrichens the mixture. Now with less spike there is less gas spurt and so the mixture is leaner.
    Having a leaner mixture at partial throttle means it will run cleaner and have more power. But the power is not coming the way the engineers originally designed. It's just an easy bolt on way to avoid modifying the needle on the NT carb as I describe on my site.
    And for this advantage there is no need to design the setup correctly using my spreadsheet.
    But these criteria give more of this leaning effect:
    bigger boost bottle
    larger diameter tubing
    shorter tubing