I've got the RWR pipe. I typically run the open end - it moves massive air, and roars like a dynosaur with an awesome deep, throaty snarl.
When I ride where spark arrestors and noise levels come into play I swap end caps and install 16 Supertrapp disks, which allows jetting to stay the same.
I first tried 18 disks, but I was too lean - 16 got me back to where I belonged so I can swap caps without jetting.

My question :

I don't "feel" a difference when I ride either way, but is there a little bit of performance to be gained with 18, or even more disks, accompanied by the correct jetting?

I'm assuming that the vacuum theory that disk systems create explains the lean-out I experienced with 18 disks, even though one might assume disks create more back pressure which would, in theory, richen the mixture.

I guess what is really needed is a dyno run of each set-up. Anybody ever had such a thing done? If the disks offer more power then I'll leave them on, of course.

 

Come on guys - it usually doesn't take this long to get somebody's response around here.
Somebody out there has had to have wondered the same thing, surely.

Disks or open end, where's the best gain?

 

I talked to Alba because Inoticed the Raptor in the newest Dirt Wheels had one of their pipes, but with a straight through end cap. I asked the guy what his opinion on it was and he said that you lose bottom end and you don't gain much up on top, plus it becomes rediculously loud. He told me it wasn't worth it. My dad who used to built pro drag bikes said that the supertrapp discs will outflow almost anything because of their 360 degree design. He said most people don't want them because of their sound.

 

Thanks dude.
I played around recently with these two set-ups, and found I could pull a higher rpm at the top of fifth with the disks on, rather than with the open end, each jetted accordingly of course.
I'm sticking with the disks.

 

If 16 disks and the strait end cap used the same jetting, but 18 disks required more fuel, then I would stick with the 18 disks[or more]. If a motor requires more fuel, that means that it's using more air. Since a motor is basicly an air pump, the more air it pumps, the more power it makes. Run more disks, add the fuel to match, and enjoy the power gain. I typicly recomend 20 disks to my customers that chose to run the disk style exhaust.

The design of the canister does a lot to determine if an open end or a disk stle will flow best. As a general rule, I usually say that an open end cap will out flow a disk, but if the canister is designed to flow with disks, the open end may come up short.

 

Knutz, Is there a point when you can have too many disks? Would that be too little back pressure, possibly causing holes in the torque curve?

 

A properly tuned 4-stroke does not need back preasure to run at peak efficiency, despite what many people have been told for years. If a motor is not built properly[i.e.-improper cam timing or profile], back preasure may help cover up problems that are already there, but that same motor would run better by correcting the problem and reducing or eliminating the back preasure.

Some people then ask, "why run any exhaust at all, if the exhaust doesn't need back preasure?". Heat control and air flow are the answers. If the motors exhaust could exit the vehicle without burning it up, you would still need an exhaust to control the heat. In order to prevent the cool air of the outside[even on a hot day, the atmospheric temp is a lot cooler than the combustion chamber] from cooling the valves, piston, etc.. to quickly, and cracking these items, an exhaust of some type is needed. In extreme cases, such as Top Fuel cars, the exhaust flows so much air, that it creates a significant amount of lift or downforce, based on the direction it's aimed. In these cases, the exhaust is needed to control the force, and direct it in a way that's benifitial to the car.

The biggest limiting factor on the # of disks to run would be noise. If you don't mind the noise, the general rule would be, the more disks the better, but at some point, added disks do not do you any more good. 100 disks, will flow just as well as 200 disks behind this motor, but aside from the weight and stress issue from 200 disks, 200 will not hurt your performance either when compaired to 100. [caution-the preceding is an extremely exagerated example, do not attempt this at home, or at least send pictures if you do, so we can all laugh]

 

Great info - I love it when things are put into a technical perspective and still make sense.
Now I have to buy another six pack of disks!