- Jardine question: To any thumper riders out there who have replaced their stock muffler with a Jardine slash-cut slip-on, I was wondering what carb rejet specs you might have found that works best with that pipe? Also, whether you replaced the stock air filter?
- SuperTrapp question: maybe the Jardine just doesn't provide enough back pressure for the Thumper? I am considering ditching the Jardine and picking up a SuperTrapp, which I am told allows for some 'tuning' (number of disks changing noise and horsepower maybe). Am I correct in thinking the number of disks changes the level of backpressure?.
- INFO: 2004 savage, Jardine pipe, 155 main, 55 pilot, half white-spacer, K&N air filter, elevation about 105 metres or 350 feet (though this varies from lakeshore (75m/250feet) to top-of-hill (270m/850feet), but appears not to make a difference). Sounds cool, but I do not like when it pops when shifting up, and a few too many pops decelerating (as for the gurgles, it is what it is I guess!). With stock pipe on and same set-up, noiseless except for the odd back-fire.

i still love the performance and sound of my Jardine, maybe its time for a upgrade!

Quote:

Misunderstanding here.  Backpressure is always detrimental.  I know, I've read what Supertrapp says, but that's not what really happens.  Scientific Design of Exhaust and Intake Systems is the bible for exhaust system design.  Less back pressure is always better.  Negative back pressure is best, and that is the goal of a correctly designed exhaust system where the scavenging effect of the sound pressure waves produces a negative pressure at the exhaust port when the valve opens.

This should be good and interesting -  

--quote--
As the piston approaches top dead center, the spark plug fires igniting a fireball just as the piston rocks over into the power stroke.  The piston transfers the energy of the expanding gases to the crankshaft as the exhaust valve starts to open in the last part of the power stroke. The gas pressure is still high (70 to 90 p.s.i.) causing a rapid escape of the gases (blowdown). A pressure wave is generated as the valve continues to open. Gases can flow at an average speed of over 350 ft/sec, but the pressure wave travels at the speed of sound (and is dependent on gas temperature). Expanding exhaust gases rush into the port and down the primary header pipe.  two basic phenomenon are at work in the exhaust system: gas particle movement and pressure wave activity. The absolute pressure differential between the cylinder and the atmosphere determines gas particle speed. As the gases travel down the pipe and expand, the speed decreases. The pressure waves, on the other hand, base their speed on the speed of sound. While the wave speed also decreases as they travel down the pipe due to gas cooling, the speed will increase again as the wave is reflected back up the pipe towards the cylinder.  At all times, the speed of the wave action is much greater than the speed of the gas particles. Waves are also reflected back up the original pipe, but with a negative pressure.  This reflecting, negative pulse energy is the basis of wave action tuning. The basic idea is to time the negative wave pulse reflection to coincide with the period of overlap - this low pressure helps to pull in a fresh intake charge as the intake valve is opening and helps to remove the residual exhaust gases before the exhaust valve closes.  Typically this phenomenon is controlled by the length of the primary header pipe.  Due to the 'critical timing' aspect of this tuning technique, there may be parts of the power curve where more harm than good is done.

Gas speed is a double edged sword as well, too much gas speed indicates that that the system may be too restrictive hurting top end power, while too little gas speed tends to make the power curve excessively 'peaky' hurting low end torque.  Larger diameter tubes allow the gases to expand; this cools the gases, slowing down both the gases and the waves.

Exhaust system design is a balancing act between all of these complex events and their timing. Even with the best compromise of exhaust pipe diameter and length, the collector outlet sizing can make or break the best design. The bottom line on any exhaust system design is to create the best, most useful power curve. All theory aside, the final judgement is how the engine likes the exhaust tuning on the dyno and on the track.
http://www.burnsstainless.com/TechArticles/Theory/theory.html

--quote--
The first misconception that needs to be cleared up is that a header relieves backpressure, but a certain amount of backpressure is needed for optimum performance.  Just the opposite is true.  A good header not only relieves the backpressure, but goes one step further and creates a vacuum in the system.  When the next cylinder's exhaust valve opens, the vacuum in the system pulls the exhaust out of the cylinder.  This is what the term "Scavenging" means.

The first consideration is the proper tube diameter.  Many people think "Bigger is Better", but this is not the case.  The smallest diameter that will flow enough air to handle the engine's c.c. at your desired Red Line R.P.M. should be used.  This small diameter will generate the velocity (air speed) needed to "Scavenge" at low R.P.M.s.  If too small a diameter is used the engine will pull hard at low R.P.M.s but at some point in the higher R.P.M.s the tube will not be able to flow as much air as the engine is pumping out, and the engine will "sign off" early, not reaching its potential peak R.P.M.  This situation would require going one size larger in tube diameter.

The second consideration is the proper tube length.  The length directly controls the power band in the R.P.M. range.  Longer tube lengths pull the torque down to a lower R.P.M. range.  Shorter tubes move the power band up into a higher R.P.M. range.  Engines that Red Line at 10,000 R.P.M. would need short tube lengths about 26" long.  Engines that are torquers and Red Line at 5,500 R.P.M.s would need a tube length of 36".  This is what is meant by the term "Tuned Length".  The tube length is tuned to make the engine operate at a desired R.P.M. range.
http://ssheaders.com/header.htm

bill67 wrote on 09/03/09 at 19:35:37:



Yes, but only if you dont jet the motor right.

Here is the theory -
If you do jet it out of the slightly lean the factroy jetted them to into the slightly rich area the motor will last longest .

Now if you do pipe and do that too you would get a longer life than if it was stock. It will be less than the above situation but more than stock.

The air filter and air box play a bigger part in the engine life than muffler/exhaust, and leave the filter stock and keep it nice and clean and fresh and it will do more for longevity than anything in the muffler.

Cool.
Srinath.

"Backpressure is always detrimental" (followed by cool theory-quotes). The theory sounds fine, but the test is in, well, the test. Anyone riding around with no slip-on, or indeed no exhaust? Hmmm. Also, note the theory given seems to presuppose twin cylinder... just one make a difference to the theory? But anyway, (degrees of) backpressure are going to be detrimental . . . the sentence needs to end with a subject, like "to some performance characteristics" (such as torque at such and such rpm, etc). Maybe the jardine/supertrapp question can be reformulated as  - anyone notice particular performance characteristics of the SuperTrapp?