2 foot long intake yields 10% boost!

Discussion in 'Performance Mods' started by andyinchville1, Nov 15, 2007.

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  1. HI all,

    In searching on the net I ran across a site that that had a calculator for determining intake length for "ramming" additional fuel into the engine to increase power....the principles of ramming has to do tuning the length of the intake runner to maximize the amount of fuel being "stuffed" into the engine when the intake valve or port is opened. You may want to check it out....kinda neat....according to different values I input we would need an intake runner of about 24 inches to coincide what I believe our max engine RPM should be (around 6000)....while the 6000 RPM is just my idea of max....the engine my go higher but mine at least stats feeling too vibration filled and noisy for me to feel comfortable pushing it any higher....heck with enough torque we could simply gear higher and go faster with fewer revs....of course you shouldn't go too low with the revs and risk lugging or overheating the engine.

    Oh...the site to look at is...http://www.bgsoflex.com/intakeln.html

    Try it you might like it....I am going to tinker today hopefully if I get off work early...I may actually go a little longer for more mid range since I really don't like to spin 6000 RPM.


  2. OK....getting ready to head to the hydraulic shop to have some pipe bent to match my home made intake flange...only problem I see is that with the 2 feet of pipe length, the throttle cable will not be long enough probably....Any fixed anybody can think of fix for that?....Other alternative I can think of is to have a bend put in the pipe so it doubles back towards the engine then it would only extend out less than a foot. Figuring in the bend radius that brings the pipe back would cut overall length but I an worried this might impede flow....of course if one were to look at the stock intake manifold you know there
    are serious problems with flow there!.....Oh well here goes!
  3. alesterfeind

    alesterfeind Guest

    This is going to look wild!
  4. Your essentially making the equivalent of a boost bottle. It's gonna look sick!
  5. OK guys...Got back from the hydraulic tube shop and they had a suggestion on how the pipe should be routed to keep lengths reasonable (see pics)...almost could act like a little fender if I put something in between the pipes! Neat thing is the carb ends up very close to where it started off so the throttle cable issue became a moot point. ....Total tubing length is 28" of 1/2 hydraulic pipe...(I think it is 1/2 inch) but the inside diameter was somewhat smaller than stock....I went with their smaller diameter with the theory that the smaller diameters would keep intake velocities up ....It is a long tube remember....we tried to make large gentle curves when possible for the same reason....Bottom line?....Engine idle speed went way up without doing anything to the carb....Throttle response was a little slower (because when you move the throttle remember the gases have a longer route to travel....so if you blip the throttle there is a slight lag.....But man the torque seems to have increased dramatically....maybe the ram thing is right!....BUT... OOPS another BUT while the lowest of the low end was improved the mid and upper end was severely hampered....Stock I could roll to 34.4 MPH....after the intake all she would do was 25 MPH....BUT again low end was great (puttering around with zero throttle was doable...this is with a 36 T rear sprocket and tuned pipe) ....with that I believe I will try the larger intake pipe diameter....reason being the smaller pipe was hindering top end more than I anticipated....standing with the bike motionless, clutch in, and revving it to the max you could definitely hear that the engine wouldn't pull the top end at all.....Something I could not explain tho was that there was a definite loud growl that seemed to be coming from the carb.....any ideas what this could be?....If I finish up work early tomorrow I will see about another trip to the hydraulic shop to try the bigger pipe but if not then it probably won't be until Monday or Tuesday until it gets done....Anybody have any alternate ideas on how the intake could be run? (I'll try to post more than 1 pic if I can).
  6. Oops attachments don't work on quick replies so here it goes again....

    Attached Files:

  7. Oh...I forgot to mention...I will probably try cutting the length a little on the pipe since I will try to tune for a max of 6000 RPM....I ordered a digital tach to better gauge engine speed...
  8. You know,now that you got the carb switched around,a tunnel ram would look cool,and you would also have...ram air!
    It would rool.
  9. mickey

    mickey Guest

    Something like a trumpet, long tube, short tube, with a valve would be cool.
  10. Heh heh heh....I did think of the ram air but have to get the thing to work first! ;-O
    Bigger tube diameter here I come!
  11. mickey

    mickey Guest

    Would an equal length tube as a velocity stack have the same effect without the throttle lag? If the effect comes from momentum in the air flow, I would think that it wouldn't matter which side of the carb the length was on.
  12. This are my suggestions.
    Andyv. since you have access to a machine&pipe shop:
    1. incorporate a reed valve too; just at the edge of the cilinder. It would help.
    2. Have you seen the megabomb MX 4-stroke exhaust pipes from FMF? If something with that shape and size is incorporated between the carb and the engine, it might work the same way pulsating exhaust gases work beter with a pipe that has a properly shaped expansion chamber.
    3.Definitely your pipe looks way too long and small in diameter. At high airflow speed rates, flow will be slowed down by friction against the walls of the pipe. Make it way shorter in lenght and with a middle section(the U bend) bigger in diameter. Make the transitions between the small and large diameter tubing conical, so that flow is not affected. You might end up with the same volume and gas mass in harmonic pulsating flow at your targeted rpms, but with a shorter pipe and with less losses caused by friction. So it might improve your power at low and higher rpms.
    All this changes would not imply more exhaust noise. All happens between the carb and engine. And no more exhaust noise, but more power is always welcomed.
    That's my humble opinion.
  13. Hmmm...Micky that is an interesting thought...haven't thought of it that way...but maybe there is something about the fuel having to be in the mixture that is being "rammed" for it to count? Otherwise wouldn't the column of air to the clouds be part of the "pipe"....well that's a little extreme....maybe it has to be enclosed somehow but then again back in the 70 - 80's when carbs were widely used before fuel injection, most of the tinkering that took place on the induction side was Carb, intake manifold, and cam (well ok porting too)....Other than ducting for cold air intake I can't recall anybody attaching long pipes to the carb to make a ram....Hmmmm...dunno but then again there were velocity stacks....Hmmm is there an engineer in the house? HA ;-)
  14. Hi Hotsauce,

    Good ideas....reed valve and all....I'm going to see how far we can go with the pipe first just since I stared on it now....I like your idea of the stepped pipe sizes but to keep it simple for now I am going to try the larger pipe to see how that works....

    Ironically I just thought of what Large about the entire pipe becoming a large boost bottle?....I wonder if that is possible....if so maybe the tuned length is the volume of the cylinder after all....but if that is the case maybe there is no ram effect after all and the best we can do is a boost bottle?.....Hmmmm...head is beginning to spin on this one....

    The noise I heard was I am pretty sure not from the exhaust note....definately sounded like a moaning through the carb?...

    Maybe If I hooked my boost bottle that would help but then again I thingk the bottle is for low speed and now the low speed seems good....

  15. Oh...the velocity stacks that I am familiar with are like little funnels into the carb throat...not necessarily super long and tall..
  16. Attached Files:

  17. sunofjustice

    sunofjustice Guest

    andyinchville, No offense......but your going in th' wrong direction. I tried running a longer manifold last winter ( 8' in length/ 20mm diameter w 20mm carb)...and even with rejetting my 70cc still felt like a dog. When I re installed th' old manifold (5"in length/ 20mm diameter) MINUS 2".......it ran MUCH better! I think th' longer th' pipe......th' LESS vacuum to pull fuel into th' engine........plus........your fuel would probably "puddle" up........and LEAN out th' motor! The new 48cc engines with th' angled sparkplug...... have litterally no manifold whatsoever! Almost like a poor mans port injection.
  18. sunofjustice

    sunofjustice Guest

    Oh yeah.......almost forgot, th' air cleaner side of th' carb you CAN go hog wild on. Most modern autos and trucks have very long and elaborate intake hoses. If you look in a pocket bike parts section......you might find a 90 degree air cleaner elbow/ v-stack combo that would help you create a ram-air system. Hope this helps.
  19. Hmmmm....after further extensive reading online about this topic it appears that the tunes length should be a good bit shorter!....Hmmm...I wonder if it all boils down to trial and error but in all fairness I think the site I listed above may have been for 4 stroke engines which would explain the long long pipe....according to 3 other sites (after I used their mathematical formulas), I am more in the area of 14 inches but then again that may be for a four stroke and would have to be halved again for the 2 stroke since we have twice as many port openings for the intake...I will tinker more....probably build another pipe (straighter ) and the lop off lengths a little at a time until I reach max speed up my test road....hopefully tomorrow if the weather cooperates.
  20. Hmmmm good food for thought....thanks Son....too bad the 8 inches that I think you used didn't work....how did you get that #?....the 3 formulas I found came to about 7 inches but then again maybe pipe diameter has something to do with it too?....I'll experiment some more....Gotta get a dyno! ;-)