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[mikebehr00]

I'm pretty ignorant on this subject but the analytical part of my brain says it only makes sense! If you move from a 96 cube engine to a 103 you're moving approximately 7% more air through the engine. If you go to a 110 over the 96 it's more like a 14% increase in air flowing through the system. If you are using any tune-able exhaust where you can add or subtract discs to add or reduce back pressure, shouldn't you have to increase discs to allow for the extra air flow? When I talked to Fuel Moto about this they say to start with 12 discs regardless of whether it is a 96,103, or 110, and I think they have a better handle on this than most. It still doesn't make sense to me. Am I missing something? I'm currently using 12 discs on my stock 110 CVO limited and it seems to run well with the power vision. I hear guys talk about their "seat of the pants dyno" and I'm not buying it. Whenever I change oil I would swear that my bikes run so much smoother but I am sure its all in my head. I want to see some empirical test and it seems like Supertrapp should have some, but I can't find it and they did not replay to my question about this (or I missed the email if they did). There's got to be a point where the increased airflow requires more discs to let the extra air out. What's the dealio with this!

[mikebehr00]

So 90 people have looked and no comments. Maybe there's way more too it and it's too hard to explain without a basic knowledge of engine air flows to begin with. I'm going to run it hard for a while with 12 discs and then add some more discs to see if I can tell a difference.

[rigidorbust]

12 discs is quite restricted , i run 24 on my 124 + i can turn å screw to run open end

[Ironhorse]

Have you considered a dyno tune? That would be the best way to determine the number of discs. On the dyno they can add or remove discs and see how the power and torque curve responds.

[grc]

SuperTrapp recommends starting with 12 discs and tune from there.  More discs equals more flow.  I copied some info I got online when I bought my 2 into 1, click on the attached pdf.

Jerry

[mikebehr00]

"12 discs is quite restricted , i run 24 on my 124 + i can turn å screw to run open end"

How did you come up with 24? Was it dynoed or just felt right? If it feels good that's great but it still seems that there should be a correlation between size of engine and exhaust outlet. I agree that a dyno tuning would zero it in but it doesn't explain why no matter the engine size the advice seems to be "start with 12 discs"! Rigidorbust uses 24 discs which makes sense as it is a big engine. My 103 ran great with whatever the stock Supertrapp came with (20 I think), but when I put the supertrapp on the 110 and watched the powervision populate the VE tables I started thinking about airflow. I'm currently running 12 and think I might have gained some low end torque, but if it stays dry tomorrow I'm going to bring it back to 20 and see if I can feel a difference.

Considering most pipes are not tuneable in the first place, I'm probably overthinking this! But it is fun to play with!

Thanks for the feedback!

"It is a tale told by an idiot, full of sound and fury, signifying nothing." Macbeth.

[stapo]

 G"day, I have a 2007 FXDSE (110CI K&N AIR filter,Power commander v, ) with a supertrapp super meg 2-1 from my experience regarding the discs is where you want the sweet spot in the power range, the more discs the higher the sweet spot in the rev range, the fewer discs the lower in the rev range the sweet spot is, that is of course running the closed end cap. I run 14 discs with a LA choppers end cap that cap be opened and closed with the aid of an Allen key, thus opening the end cap or closing the end cap in seconds which i find much quicker option, best of both worlds in a matter of seconds for adjustment.

Happy safe riding to all.