| Author | Message | ||
     Griffmeister |
Got a good deal on a stock XB muffler from another Badwebber so I needed to at least make the outlet fit the ULY. My question is does anyone know if changing the size of the rear chamber has much of an effect on engine running or sound? On the stock unit, there is a baffle at the rear jacking point. Beyond that you have about four inches in length of pure open chamber with the exception of the space taken by the outlet pipe. My plan is to take away three inches of that chamber and run the outlet straight out the back. This leaves a volume in the chamber that is still larger than the tubes in the muffler so I can't imagine this causing any restriction. Other home improvement type work have put this project on the back burner so I have time to consider how I want to finish this up. Any thoughts on the subject would be appreciated. Thanks. | ||
| Reepicheep |
Exhaust tract length is critical to performance, and I believe the change you are describing will change it. Volume is important as well, and you will be changing that as well. | ||
| Etennuly |
I simply put a second outlet on the right side of my rear chamber. It gives the bike a nice slightly louder exhaust note without loud drone that is bothersome on long trips. It sounds awesome. I had to use a smaller outlet pipe on the right side to clear the belt and swing arm. It leaves all of the stock actuator and stuff in place and did not require any changes to the stock ECM.    Did I mention it sounds awesome without being too loud?  | ||
| Slowride |
I could be completely off base here, but on my first Uly, I had Odie mod a stock pipe (SPecOps) and he did something very similar to what you are proposing Griff. Take a look at some of his stuff. He did good work! | ||
| Griffmeister |
Etennuly, by doing that you just eliminated the second and third exhaust tube and let the exhaust flow from the first tube exit straight out. No wonder it's louder.  Slowride, I've looked at some of Odie's stuff and was thinking of something similar to his dual rear outlet. It's a little tricky to center the outlet since the third tube, which is the final exhaust, is not centered in the muffler. I mocked up a Y pipe out of some cardboard tube to practice getting the angles right. If I offset the Y just enough it should center it in the endcap. Also want to put in a slight downward angle. I think Odie gets a little more extreme and tweaks the center section where the valve is, but that's proprietary information. I'm just messing with the rear chamber. Reep, as far as volume, the chamber will still have more volume than the tubes that feed and exit it. It's just that total volume will be less than stock. Just kinda wondering what such a large volume does for the actual function of the muffler. Guess if I continue as planned then I will find out. I'd like to post up some pictures of what I'm talking about but am totally useless when it comes to managing files. Maybe because I don't have any real photo software, just the windows media group that comes with the OS (WIN 7). Cannot figure out how to make an acceptable file size and embed it in the post. Oh well. | ||
| Reepicheep |
I know a two stroke dirt bike is the most extreme example, but the principals are the same for exhaust scavenging. On a KDX-200 (which I own) taking 10% of the volume of the expansion chamber will make a day and night difference in power delivery, even if done "right" with well engineered expansion chambers. A desert pipe is tuned to make big power at high RPM at the cost of low RPM power, and it has about a 12" circumference. A woods pipe is tuned to make good power at lower RPM, at the cost of some high RPM power, and it has about a 14" circumference at it's widest point. So it's not a case of "just don't go too small". Both overall exhaust tract length and exhaust volume will matter, and the right answer will depend on your specific goals. And it's not just a single "answer" where you are calculating the "right size", both those variables as they change will change the shape of a line on a power versus RPM plot. And to get a good pipe or a bad pipe up to it's potential, you need to get the fueling right. That's the real value proposition of the Drummer or the Micron pipe. Particularly with EBR pre-mapped ECM's for sale that match them. Getting these things to their full potential is a MAJOR engineering challenge, think months to years of work. It's hard to justify that if you are doing it for just your pipe, but easy to justify if you are selling bikes or exhausts with maps. You can likely cobble something together and get it to work, it just won't be very well optimized. | ||
| Etennuly |
My "test pipe" was actually an experiment for relieving heat from the exhaust system one hot some-gun of a summer. It was done to eliminate the possibility of an internal restriction in the system. At that time the bike was having a problem going into run-skip every time the temperatures reached 70F+ and I tried to run at 70+ mph. The muffler would radiate enough heat that I could feel it in my boots. That is why I used a smaller diameter pipe and it is the length that it is, to get the heat out beyond the belt and swing arm. The additional loudness is not nearly as loud as you might think. It simply lets some of the noise and heat have an escape route. It had no effect on performance, power or fuel mileage. But it does sound awesome without being annoyingly loud. | ||
| Griffmeister |
Yeah Reep, back in the 60's and 70's 2 stroke cans were pretty much tuned to one specific RPM. Performance generally dropped off above and below that speed so you needed a tuned pipe that was specific to your riding needs. I thought one of the manufacturers came up with a variable chamber at some point in time but I can't remember who. At least 4 strokes are a little more tolerant of change. I haven't finalized my design yet so I may still change the chamber some but still want to go with a rear exhaust. Etennuly, If you're roasting your boots then that is HOT. I can't imagine what the rest of you felt like. On those days that didn't drop below 90F I pretty much headed to anything that had A/C whenever possible.  | ||
| Reepicheep |
My KDX (and many other two strokes) have some kind of "power valve". On the KDX, it is called a KIPS unit, and it is basically a wedge on a threaded rod that sits at the top of the exhaust port. The threaded rod is turned by a spring loaded intertial spinner (that is really easy to break when you take the top end off). At low RPM, the wedge is driven in, which effectively lowers the top of the exhaust port giving a little longer stroke and higher velocity. As the RPM's climb, it retracts and opens the port to normal size. And it rattles at low RPM.  Works pretty well in spite of it's mickey mouse looking nature. And in spite of that feature (which makes a huge difference), the pipe diameter makes a huge difference as well. With a dyno and exhaust gas analyzer, and a few months of work leaving a pile of scrap pipes and abandoned fuel maps, you could probably get many setups to work well. I don't know if just the stock O2 analyzers and megalog will be an adequate replacement for a dyno and EGA, seems like there would be a lot of uncontrolled variables and a pretty narrow squinty view of what is really going on (like trying to find a lost set of keys on a football field through a microscope). | ||
| Teeps |
Anyone mod their stock muffler? Yes, I removed all the insides and installed a Cheery Bomb glass pack. Rebuilt the bulk heads, so the muffler could still be used for raising the bike. The finished muffler looked 100% stock to the untrained eye, only tip off that something was not right was the MIG Weld stitches. Alas, after 10k miles one of the rebuilt bulkheads cracked and the muffler rattled like mad. So I reinstalled the stock muffler, which is still on the bike. Performance wise, there was a small hole in the low end torque; but above 3500 rpm it ran strong. | ||
| Rwcfrank |
I modded mine and tried a million different style before hitting what I think is the perfect combo of top end with no loss and perhaps a slight gain on the bottom, my only complaint is the noise that emanates to my helmet. I have had others ride the bike around my street and down the road and its not loud at all, It sounds really great but all of the noise seems to get to me. Other than that it flys and it sounds great. I have an EBR ECm so that helps, I also retained the valve with my design. |
