Extending the carb-engine intake pipe as a performance mod???

Discussion in '2-Stroke Engines' started by bakaneko, Jun 1, 2016.

  1. bakaneko

    bakaneko Active Member

    Hello. I don't have a 2-stroke but was watching a video from Brian Nole (love that dude) and he mentioned that if you have the space you can extend the intake pipe distance (3inch min) from the carb to the engine as a performance mod. He said combined with an expansion chamber or bigger exhaust and a hotter plug. This will allow more gas to flow into the engine. This kinda make sense to me but wanted to see what you folks think.

  2. skyash

    skyash Active Member

    one motor i got has a short one maybe 1 inc long i wood think it wood let fuel get in faster /more then a long one
  3. jaguar

    jaguar Well-Known Member

  4. HeadSmess

    HeadSmess Well-Known Member

    its a tuners trick...

    one, remove exhaust, completely, so it doesnt affect any exhaust flow characteristics.

    two, make a really long manifold.

    three, start trimming bits off manifold until you feel it pulling at a desirable RPM. this entails a LOT of test rides.

    four, once the intake length suits the intakes port times, you can design a tuned exhaust to suit that rpm.

    the two effects together go hand in hand and boost performance.

    it has nothing to do with letting fuel in faster or not, its all to do with pressure waves that reflect up and down the manifold due to the closing and opening of the piston port. get the length to suit the timing and the RPM. and then the fuel gets in faster regardless of the length. as its already flowing towards the intake port as the port opens. for a certain intake duration, theres a definite length that works best, at a specific rpm (or two, due to harmonics)

    its like tuning a trumpet in a way...

    i suppose i have to link it again...

    Intake-tract “tuning” will be vitally important no matter what kind of time-area is
    provided at the port window, and it is all too easy to get the pulsations out of phase with
    the piston by altering the intake timing. All alterations in intake timing should be
    followed with a careful check to determine if matching alteration of the intake tract
    length is not also required. Although this kind of work should be validated by actually
    running the engine with a stub exhaust attached, as outlined elsewhere in this book, a
    preliminary check may be run mathematically, using the formula for finding the resonant
    frequency of the necked flask formed by the crankcase and intake tract provided in the
    chapter on crankcase pumping.

    and somewhere else...

    And that effect will be unmistakable, for the engine will pull very strongly when
    it comes “on the pipe”. You will also find that intake pipe length can move the stub
    exhaust-equipped engine's power peak over a very wide speed range. My friends at
    McCulloch, who acquainted me with the stub-exhaust testing technique, tell of tests they
    have performed with an engine having an intake period of 120-degrees, and with pipes
    ranging from 5- to 9 ½-inches in length they were able to move the power peak anywhere
    from 3000 rpm to 8000 rpm. The 9 ½-inch length gave substantially the same power at
    3000 rpm and 4000 rpm; at 5000 rpm, an 8 ½-inch was best; at 6000 rpm and 7000 rpm
    the same power could be had with either a 9 ½- or 6 ½-inch length; and the same was true
    at 8000 rpm, but with lengths of 5 ½and 8-inches. From these tests, it was determined
    that the best compromise length for the entire range 3000-8000 rpm was 8-inches; a 5 ½-
    inch length was slightly better for the range 6000-8000 rpm. It should be understood that
    these lengths only apply to this specific example, and would vary with any changes in

    intake timing, crankcase volume and intake tract diameter.

    read that last bit twice!

    the actual length will vary depending on engine, capacity, and any modifications made, etc etc etc... so you have to do your own experiments...sorry :confused:
    bakaneko likes this.
  5. bakaneko

    bakaneko Active Member

    what he said... ^
  6. justakid108

    justakid108 New Member

    I use a vacuum tube, if anyone cares...