Originally Posted by MotorBicycleRacing
The best mod bang for the buck is an expansion chamber.
What do you mean by a straight pipe for a 2 stroke?
Straight pipes sort of work on 4 strokes.
The goal of a tuned straight pipe in this application is to use the reflected negative pressure waves from the open end of the pipe to help draw out the exhaust gases. By selecting the appropriate length of the pipe, the reflected rarefaction wave arrives at the exhaust port just as the transfer port opens thus assisting the flow of fresh mixture into the cylinder, and exhaust gases out of the cylinder. The figure below illustrates this action. In the figure, even though the piston has reached bottom dead center (BDC), fresh mixture continues to enter the cylinder because the rarefaction wave causes P2 to be smaller than P1. A key point to note is that the velocity with which the pressure and rarefaction waves travel down and up the exhaust pipe is for the most part independent of the engine operating frequency (RPM). Due to this fact, the conclusion must be made that for a given pipe length there is an optimal RPM for which the waves will arrive producing the greatest benefit for the breathing of the engine.
At this optimal RPM, the engine breathes significantly better and hence produces a noticeable increase in output power. This effect is quantified by calculating the ratio of fresh mixture to exhaust gases within the cylinder as the compression stage begins at EPC. If the rarefaction wave is very large, it is possible that fresh mixture is pulled into the exhaust pipe while both transfer and exhaust ports are open. This phenomenon is known as short circuiting the engine and produces undesired effects such as a decrease in fuel economy and an increase in release of volatile organic compounds. These negative effects can be mitigated by designing the exhaust system such that either no fresh mixture is pulled into the exhaust pipe (i.e. perfectly tuned straight pipe)
or further utilizing the exhaust pressure wave to inhibit short circuiting. For performance two-stroke engines, the second solution is most often employed by means of a tuned exhaust pipe known as a tune pipe.
strait pipes work on 2 strokes as long as they are the correct length ! they are most effective at high rpm riding like WOT aplications. the length is made so the wave exits the end of the pipe at just the right time to create a slight suction to aid with pulling in the intake charge . though not as good as a tunned x chamber its cheap and WORKS
!!!! the highest top speed i have achieved on my bike was with a tunned striat pipe !
of course there is a dissadvantage also...
Of course those waves don't radiate in all directions since there's a pipe attached to the port. Early two strokes had straight pipes, a simple length of tube attached to the exhaust port. This created a single "negative" wave that helped suck spent exhaust gases out of the cylinder. And since sound waves that start at the end of the pipe travel to the other end at the speed of sound, there was only a small rpm range where the negative wave's return would reach the exhaust port at a useful time: At too low of an rpm, the wave would return too soon, bouncing back out the port. And at too high of an rpm, the piston would have traveled up the cylinder far enough to close the exhaust port, again doing no good.
Indeed, the only advantage to this crude pipe system was that it was easy to tune: You simply started with a long pipe and started cutting it off until the motor ran best at the engine speed you wanted.
its the easyest damn mod to do a 1in aluminum strait pipe !!! make it too long and then cut 1in at a time till you get it to the driving rpm you use most and you will always have power in that rpm range. want to change it ? add another inch or take off another inch ! soo easy but it only gives a small but powerfull power band. a tunned x chamber will definatly give you a broader band but cost a lot more and is more difficult to make . try it out some time if you wan to play aroung with small but powerfull rpm ranges !
i am a cheap baStrd so i make strait pipes for my motors at the given rpm i ride that bike at most and so far i have had great results though i know not as good of results as if i had a propper tuuned x chamber but my girly wont weld me any more complicated stupid bike parts lol her words... at least i got 1 good tunned pipe out of her lollollol