2 foot long intake yields 10% boost!

[mickey]

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.

 

[hotsauce492003]

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.

 

[andyinchville1]

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 ;-)
Andrew

 

[andyinchville1]

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....

Andrew

 

[andyinchville1]

Oh...the velocity stacks that I am familiar with are like little funnels into the carb throat...not necessarily super long and tall..
Andrew

 

[Large Filipino]

I think you should do this. It would be MOST awesome.
With a reed valve,would it have a powerband like them 2 stroke enduro bikes?

http://www.turbokart.com/turbo_exciter.htm

 

[sunofjustice]

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.

 

[sunofjustice]

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.

 

[andyinchville1]

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.
Andrew

 

[andyinchville1]

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! ;-)
Andrew