Tuned performance pipe for Spree...

[noiseguy]

No, that pipe is too long. Less length would help. What I meant was use the pocketbike downtube as a length gauge.

Here's the V2 pipe:



Note it runs closer at the bottom. This is how the pipe has to be proportioned to work right.

This expansion chamber's tuned to 10000 RPM, so it doesn't work as well at low speeds (launch.) The pulley mod makes the launch even worse. At anyrate, the motor run nicely with this pipe at high RPMs, so 35 MPH doesn't seem to be a problem, even without the pulley mod.

I'm selling the pipes for $80, but the buyer needs to mail me a donor downpipe. PM me if anyone's interested.

[darat]

thats sweet.

[Spreewell]

That looks like a trick as shizz braaaaap can Noiseguy. Good work!

[85stroka]

if you made the transition smoother,it would be a * of alot better.

[noiseguy]

if you made the transition smoother,it would be a * of alot better.

It would look better; it would function the same. Keep in mind this thing is breathing through a .5" hole in the back. The acoustic resonance of the pipe, which is the important thing, and doesn't change with this type of junction. Only the length is important.

[MySpree]

personally i would etlast weld some sheet metal over it just to make it look nice... but thats just me i liek things to look good, like make it a skin.!

[85stroka]

if you made the transition smoother,it would be a * of alot better.

It would look better; it would function the same. Keep in mind this thing is breathing through a .5" hole in the back. The acoustic resonance of the pipe, which is the important thing, and doesn't change with this type of junction. Only the length is important.

I am sorry but it's a pressure wave,and the smoother the transsition the better, go look at some 2 stroke gp bikes,look at how smooth the transition is,it aint for looks, the smoother the transition, the less resistance and the less speed the pressure wave looses.
Your telling me as a sound wave hits that bend it aint gonna make a difference?

[Farfignugin]

he does have a point...
if a soundwave hits an angled surface its bounced in a different way than if it hits a smooth round surface....

[noiseguy]

I am sorry but it's a pressure wave,and the smoother the transsition the better, go look at some 2 stroke gp bikes,look at how smooth the transition is,it aint for looks, the smoother the transition, the less resistance and the less speed the pressure wave looses.
Your telling me as a sound wave hits that bend it aint gonna make a difference?

I'm going to make one more pass at this and leave it alone. I've worked off and on as an acoustic engineer over the last 10 years, so my ability to explain in layman's terms can be wanting at times. Guys on Mopedarmy pointed this all out too, but I didn't bother to elaborate there.

1) You have to curve the pipe, so whether its a sharp angle curve or gradual (as you propose) it has to be there. If we treat the acoustic propagation as a ray, it will reflect back to the port regardless of the construction of the pipe. The "sound ray" paradigm is often used to explain echos outdoors.

2) The acoustic wave propagation is really more like a wave, because its been trapped in a bottle: the expansion chamber. Basically, it acts like blowing across the top of a bottle. When you blow, the noise is not caused by a sound ray (or air) boucing off the bottom of the bottle to the top. It is caused by excitation of the acoustic mode of the interior bottle shape, which makes noise. The fact that the expansion chamber has a hole in the bottom is immaterial. Having looked at more computer-generated interior acoustic mode plots that you would care to hear about, I know from experience that the most imporant part of the design is that the length is right. They are very insensitive to configuration, like for example bending them at an angle to go around the fan shroud.

3) The smooth design you are refering to is great for medium to high volume production (1000 - 100K+ parts). It is done by hydroforming the part, and is cheaper/easier from a labor perspective. Since I'm making about 5-10 of these tops, I'm not going to invest in the equipment to make the pipes this way. The way that I'm building them is the way an engineering shop would make development prototypes, because that's what I'm typically involved in. Prettying things up I leave to others.

Kurremkarm is picking up the first V2 pipe. We're thinking about respacing the drive pulley out rather than messing with the clutch, to help launch.

[85stroka]

Ok, I understand what you are saying so why then do then make them so smooth? and I am not talking hydro formed either, we are talking about gp bikes, either street or race,any hand made pipe.

[MySpree]

well then put a skin on it.!

[noiseguy]

Ok, I understand what you are saying so why then do then make them so smooth? and I am not talking hydro formed either, we are talking about gp bikes, either street or race,any hand made pipe.

I think you're refering to pipes without strong cone transitions, ones that are progressively shaped into a chamber. All the theoretical work I've seen, and chamber calculation software, uses cones as a basis for design. From what I've seen, the progressive pipes seem to follow the same guidelines, but there's likely some actual reason based in testing or manufacturing that supports that design. I still think that the real reason is financial; they're easier to mass-produce and much more flexible in terms of packaging.

[85stroka]

Ok, I understand what you are saying so why then do then make them so smooth? and I am not talking hydro formed either, we are talking about gp bikes, either street or race,any hand made pipe.

I think you're refering to pipes without strong cone transitions, ones that are progressively shaped into a chamber. All the theoretical work I've seen, and chamber calculation software, uses cones as a basis for design. From what I've seen, the progressive pipes seem to follow the same guidelines, but there's likely some actual reason based in testing or manufacturing that supports that design. I still think that the real reason is financial; they're easier to mass-produce and much more flexible in terms of packaging.

Maybe, I not sure what the term is called, but I just know that certain pipes out perform others,and a way to tell is how the chamber itself is made, hard cut angles verse smooth bodied ones?

[noiseguy]

Performance from pipe to pipe probably has more to do with design charectoristics (in this case) than construction technique, at least for expansion chambers. The kidney shape of the newest wave of pipes is interesting, but I have no design background on those. Perhaps I should try copying one?

For example, go into Perf Tech Docs. There's a pipe calculator in there, based on 30 y/o work done with 2-stroke tuning by Jennings (I have more recent formulas, differences are minor). It will design a pipe for you based on a given displacement, intake and transfer porting, exhaust temp, etc... lots of variables. Play with exhaust temp, that makes a huge difference in the pipe.

Work with it for a bit and you'll find that the calculated design changes slightly with porting and displacement changes. Changes in jetting, fuel octane and compression affect exhaust temp. Given all these variable, and the different jugs out there, with slightly different portings and displacements, it's not surprizing that certain pipes work better than others. In my mind, the pipe and jug should be design (and sold) together.

Reality is that you'll get 75% of the way there, even with a suboptimal pipe design. That last 25% is what takes tuning, once you've bought the parts. From what I've seen with these pipes I've built, once you've gotten the bike lauched the improvement in performance is dramatic. They're just a lot more fun to ride from 15 - 35+ MPH.

[darat]

i wouldnt really care what it looks like as long as it gave me a extra boost.