Emulating Low Gears

Discussion in 'Spare Parts, Tools & Product Developement' started by DuctTapedGoat, Jan 30, 2011.

  1. DuctTapedGoat

    DuctTapedGoat Active Member

    By extending the air intake, you get more low end.

    You will get the SAME effect from using a larger intake mount, as long as the internal cylindrical volume is the same.

    I typed this up last night and fell asleep at the desk. Here it is...
    I just finished extending my intake! I got about the 8.5" extension, and SWEET MERCIFUL TROUT, it's like a whole new world is opened up to me.

    You know on old diesel trucks how you start off the line in second? After this mod, I feel like I've been in second gear on my bike it's entire life. This mod brought me down to below first gear. Now, I only took it about a quarter mile to see the initial results, as it's 10:30 at night and it's cold. Tomorrow in the daylight I'll jump and take it on a mile and see where it does in the long haul. There is SO much throttle response it's seriously crazy. It's going to take about 30 minutes to dial everything in, my throttle is right on the brink of screaming and sputtering out at the same time. But like I said, WOW. It's handling so delicately! I want to just go find a huge hill and just climb it over and over again!

    I know what I'm doing tomorrow, and that's tinkering!!! There's something here and I can't quite place my finger on it, but I know I'm onto something big. It's not just the distance! That's a part of it, but that's not everything here, it's all about the hose diameter. A smaller hose means there is less distance for the fuel vapor to travel.

    Okay, now wrap your minds around this...

    Instead of just playing with standard hosing extensions, what we should be doing is calibrating this with MULTIPLE hoses.

    Standard intake is .75" ID and 2.5" long. That means it's got a volume of 1.1039 sq inches (estimate). An intake at 8.5 inches long is 3.7533 sq inches. Collective, we've got a total volume of 4.8571875 square inches for an 11 inch intake pipe at .75" ID (which is what I'm running now, VERY VERY low end).

    Now, that's awesome, right? Lots of numbers. But, this is where it gets good. If you use only a half inch intake pipe at only a total of 8.5 inches long, you get 1.668125 sq inches of distance. Running two simultaneous intake pipes will get you 3.3625 sq inches. A third hose will bring that up to 5.030625 sq inches.

    In theory, we're looking at basically one point seven square inches for your closest to stock setting, which as I said, feels like second gear on an old truck off the line. Say we were to use two intake pipes now! We're looking at three point four square inches, which is double the intake. Running both of these intakes at the same time should yield a decrease in top speed, but an increase in acceleration. That's basically your "First Gear". A third intake hose brings it up to 5 square inches, which is where I'm at currently tonight, this would be the "MegaDrive" gear. Lastly, we have a fourth hose, which is 3/8ths hose.

    To sum,
    "MegaDrive" = All three hoses ON.
    "First Gear" = Two hoses ON, One hose OFF.
    "Second Gear" = One hose ON, Two hoses OFF.


    Like I said, I was tired when I was doing this and I know there ARE other variables, but this is just kinda the foundation.

    Also, this is going to be part of my dual carb setup down the line, but until they are both done, they will remain separate projects.

  2. shell shock

    shell shock Member

    im having a hard time wrapping my head around this.. concept sketch? dont mean to sound ignorant.

  3. DuctTapedGoat

    DuctTapedGoat Active Member

    Just picture the stock intake tube, now picture it with a Y on the end, but meeting up at the carb with a valve on each tube.

    Then just add extra tubes, like one that forks into 3, 4 intakes which all meet up at carb.
  4. shell shock

    shell shock Member

    ohhh! i get it! thats a really good idea!
  5. DuctTapedGoat

    DuctTapedGoat Active Member

    I know! It's gonna take some time to get all the parts I'm going to need to make a prototype. It sucks that there's no way to get it working to emulate higher gears, if you tried you'd be making a way too complex choke. But just for the hill climbing aspect, it's a very worth while thing.
  6. shell shock

    shell shock Member

    you my friend, will revolutionize MBing, really, ive been here for like what.. a week, and ive already overflowed my brains float valve with your ideas! ^_^, hurry up and proto already!

  7. DuctTapedGoat

    DuctTapedGoat Active Member

    I got paid today, so I'm going to start hunting around for parts. It's gonna take a while to get everything, tough parts are going to be customizing the intake tube and finding valves that are the right size to keep flow proper.
  8. give me vtec

    give me vtec Active Member

    why not just get a bike with a shiftkit and derailuer?

    they relly are fun... believe it or not, i actully have a first and second gear.... and five others to with them.
  9. shell shock

    shell shock Member

    @ DTG, sweet! hmm, me thinks a cheap pipe brazer would be sufficient to join the intakes.. least for a proto anyways.

    @ G M Vtch, im not sure about duct tape goat, but to me, half the fun of this hobby is DIY. sure, you could buy parts, but... making another way is so rewarding.
  10. DuctTapedGoat

    DuctTapedGoat Active Member

    VTec - http://www.sickbikeparts.com/catalog/index.php?cPath=21

    Tubing is cheaper than 150 bucks! If I had the money, I'd do it in a heartbeat. But, I don't have that much - heck, for 150 I could buy a second motor for a rackmount. I'm seeing what can be made for less than 25.
  11. give me vtec

    give me vtec Active Member

    understandable... hope you get what you are looking for.
  12. HeadSmess

    HeadSmess Well-Known Member

    ok, i think i get this.... or what your trying at. variable intake length/volume.

    i read it, thinking...no, wait...its LENGTH LENGTH LENGTH! but.....

    when designing a speaker box, you cant care less at the actual individual dimensions, as long as you end up with the desired VOLUME....... but im still doubtful wether this works when dealing with induction pulses in a pipe in an engine... but still, it is sort of like a bass reflex system...sooooo. im not going to stop you, it might just work... and hey, its great when that happens!

    if i was you, id be scouring scrapyards and pawnshops for.... A TRUMPET! three airtight valves, three different lengths of pipe already attached...

    or look up how the valves work... theyre not thaaaat hard to make...
  13. loquin

    loquin Active Member

    Actually, while the volume of the speaker box is critical, the individual dimensions are also quite important.

    Each dimension of an enclosure has a specific frequency associated with it. This is the frequency whose wavelength is the same as the dimension. And, you can get standing waves at that frequency, and at every multiple of it. This makes the sound at the standing wave frequency (and multiples) somewhat louder than at other frequencies. (Resonant peaks) If your enclosure has two sides the same length, the sound spikes will be worse, and it will be worse yet if the box is in the shape of a cube, because the standing wave will triple amplified. Ideally, the three sides of an enclosure should be approximately .62:1:1.62 ratio. This will reduce the resonant peaks due to standing waves to a minimum. This ratio is also known as the 'golden ratio.'

    In the case of exhaust tubing for tuned pipes, both the pipe diameter and the pipe length come in to play, and they interact with each other. The smaller the pipe diameter, the slower the pressure pulse propagation through it. So, the length increase would need to be greater than you would otherwise expect if you just calculated a length based on a constant volume.) Also, as I recall, the velocity change due to tube diameter change is not linear...

    The same effect (slowing due to tube diameter reduction) on a much larger scale is what causes tsunamis to build height near the shore. As the water gets shallower, the leading edge of the tsunami slows down, (it's 'tube' has gotten narrower) and the later stages of the pressure wave push into it. Since the water is incompressible (relative to air) the increased water volume in the same square footage (as seen from above) forces the level of the water up...
    Last edited: Feb 1, 2011
  14. give me vtec

    give me vtec Active Member

    Are you an old school car stereo guy?
  15. loquin

    loquin Active Member

    More for home stereo - wrote a Thiele-small program for loudspeaker design in the early eighties. On a mini-computer, the size of a washing machine, no less!
  16. loquin

    loquin Active Member

  17. give me vtec

    give me vtec Active Member

    Wow... That is super cool! You can guess where my next $14 is going.

    That will go well with the new millermatic we got at the shop...
  18. loquin

    loquin Active Member

    Here's an idea: Think trombone, rather than trumpet...

    Change the length of the tuned pipe, by using a U-Shaped sliding portion of the tube. Move the U away from the engine and the pipe gets longer (and is more effective at lower RPM.) Slide the U-tube towards the motor, and the RPM tuning goes up.

    Ref the sketch, below. I assumed stainless bellows to seal the U-Tube, but, you could use something similar to piston rings to seal it, I suppose...

    If you were REALLY good, you could come up with a centrifugal 'clutch' sort of arrangement to automatically tune the pipe to the engine RPM!

    Attached Files:

    Last edited: Feb 1, 2011
  19. loquin

    loquin Active Member

    Yeah - I dropped the $14, too! :cowboy2:
  20. DuctTapedGoat

    DuctTapedGoat Active Member

    Nice! This is much better than the on off valve concept - immediate on the fly length adjustment! I'm going to have to go back to the drawing board. The only thing about that is it's a very long length at it's shortest length, and only gets longer...