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2013 Stock exhaust question

2K views 17 replies 7 participants last post by  NyteStalk3r 
#1 ·
This may be obvious to someone else, if so, please enlighten me.

When looking inside the upper exhaust hole in the stock muffler of my 2013 CBR, just inside the hole, I see what looks like a round, shiny steel cap, held on by two screws, that seem to be covering up (partially) that exhaust pipe/hole/whatever.

Before I try taking it off just to see what it is (the screws are visibly locktited with red Locktite or paint), can anybody tell me what it is, and why its there?

It looks like its somewhat RESTRICTING the flow, but maybe there's a good reason for this. Due to the small diameter of the upper hole (even though its larger than the lower one), I can probably take it off, but if I find its necessary, it may be tough putting that plate and those screws back in.

Anyone know? :popcorn2:
 
#3 ·
That's the exhaust flapper. It opens up automatically via a servo motor near the battery when you get your RPM's up. You don't need to mess with taking it out, just do the exhaust flapper mod which will keep it open permanently. Do a search on the forum here, and I'm sure you'll find the step by step instructions. It's super easy, and should only take you 5 minutes. Pretty sure there's some YouTube vids showing how to do it as well.


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#4 ·
Thanks for the replies. Found several threads, and a couple of videos.

There seems to be some disagreement in the responses, as to what effect disconnecting the cables have. Everyone agrees it increases exhaust note. Not everyone agrees it has any benefits besides that.

I certainly don't wish to lose any smoothness or torque at low rpm.

Without a consensus on benefits of fooling with it, I will likely just leave it be.

Thanks again for responding :th_salute:
 
#5 ·
I've got a 2013 (all red) 1k, and I did the mod on mine. Exhaust sounds MUCH better now, and there was zero side affects. All you're doing is moving the servo motor so that the flap is in the open position, then disconnecting the cable from the servo so that the flapper stays in that position. The servo will continue to go back and forth, it just won't be moving anything. Now, some say that having the flapper open all the time will give you more HP in the low range. I never got dyno'd, so I can't attest to that, BUT, I can tell you there's been no negative side effects at all (no rough idling, etc). Maybe that was an issue on other years? But its not an issue on our 2013's. Give it a try man, if you don't like it, just hook the cable back up. It's worth 5mins of your time, and I'm pretty sure you're gonna like the result.


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#11 ·
I did the flapper mod on my '08 the day I got it. Didn't seem to increase performance, but didn't hurt it either. The best part is it didn't sound like a Prius anymore. Flapper mod takes 10 minutes TOPS, and if you're not getting an aftermarket exhaust anytime soon, I highly recommend it.
 
#13 ·
I actually didn't get to it, mostly because I was stuck trying to do the Intake Flapper Mod, and having trouble understanding just what is happening there.

There are more pages on that Intake Mod than I would've ever imagined, but after taking both sides upper fairings, and looking at how it works, I KNOW I'm missing something :deadhorse:

Both sides flaps CLOSE the air passages, as the solenoid PULLS UP on them at around 5-6k rpm (bike in gear, on rear stand). This seems to me that they're BLOCKING air flow back to the air filter box. Since I couldn't figure out just how this works, I put everything back together, but by then I was out of time to test the Exhaust Flapper disconnect (which as stated above by others, was extremely simple).

I have to start over on this sometime this week.........:dazed052:
 
#14 ·
I think that you actually have more torque at lower rpms with the flapper working unless you install a Power commander or such and tune it. It won't effect wfo throttle but down low I remember someone on here showing how on stock systems that it actually decreases torque down low. Sounds better but....
 
#15 ·
Yep... this is most likely correct.

Honda tuned everything to match. If you mess with something, it can cost you a little power somewhere.

The exhaust flapper helps make more torque right off idle.
It also makes the exhaust as quiet as a scooter.
If you open that flapper valve all the time, you do lose a little bit of throttle response right off idle.
You notice it when taking off from a stoplight.
The good thing is: who cares!
This bike is super strong in the low to midrange. So you don't even miss it.
I would rather have a little better sound. So I left the flapper open with the cable disconnected.
It has NO EFFECT on power above 3k rpms, and only a small reduction off idle.
 
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