Exhaust flapper valve--what does it do and do i need it?

Last year I bought a new-to-me 2010 Camhead RT. Sweet bike. The previous owner had installed a full Remus exhaust system -- from header pipes to exhaust. Remus eliminates the crossover, and Catalytic converter, keeps the Oxygen sensors and the 'flapper valve', and has the titanium muffler. Has a nice sound to it, but recently found it a little annoying.

 

Last month I swerved into a killer e-bay deal for a COMPLETE brand new stock exhaust take-off from a 2012 (the owner probably did the Reumus swap on his brand new bike [no bluing on header pipe]). I switched the mufflers (Remus for Stock), but left the rest of the Remus plumbing, including the stock flapper valve.

 

Now I am trying to install a Bushtec trailer hitch, and the control box on that stupid flapper is RIGHT IN THE WAY.

 

Question: what does that little devil do, anyway? Can I remove it and replace that section with a short standard piping in that section, or do I risk the wrath of the Teutonic Gods or CANBUS or BMW computer? I'm thinking without the flapper (in its variable position) and without the Cat, that engine should be breathing pretty darn good.

 

Your comments appreciated

I believe it is an emissions device & at lower RPM's it provides a little bit of "back pressure" which gives you a little more torque. I bought the "Flapper Eliminator" from Wunderlich to get rid of it as an experiment.

 

The Canbus won't care, but it will show up as a fault code on a GS-911 or the Dealership's computer. I did not notice any more noise either.

 

I put it on one of my Camheads and I noticed it made no difference to me, except it was about 4 lbs lighter and combined with a K&N filter and PC-V there is a little more power for passing. But all 3 components must be on at the same time to notice much of a difference. Got great mileage too.

 

Or get the newer AF-XiED for R1200's from Beemer Boneyard, it will help you pull what whatever you are towing. With all that air flow, a little extra gas will help: BeemerBoneYard

 

Once you get under the bike the flapper motor is very easy to take out too.

 

Good luck!

 

http://www.wunderlichamerica.com/motorcycle/R1200RT/8166209.html

 

 

 

Edited July 13, 2014 by RSH

I removed the flapper and servo motor on my 2013. I left the cables attached to the flapper unit and removed both as a unit. I then covered the electrical connector (on the bike side) with a rubber boot. Nothing shows on the dash. I also bought the connector pipe from Wunderlich. Others have bought a piece from welding shops or muffler shops, for less. Quite a few R owners have removed the flapper and a search will even find forum sites with picture step by step instructions. I've been told by more than 1 BMW tech that it is a noise reduction unit, even if marketing sells it as a "tuner". IMHO, it's a noise reduction thing. This link may help. http://www.ukgser.com/technical/nick...%29%20V1.1.pdf

Edited July 13, 2014 by 1200bc

This is a very good link posted by 1200bc & comprehensive too. Always learning.

 

Flapper Removal & Why

Don't you just love self-appointed motor geniuses?

 

From the 2/2008 issue of BMW Motorcycle Magazine in its article on the introduction of the HP2 Sport ...

 

An exhaust flap in front of the muffler is actuated by an electronically controlled servomoter via a cable. This constantly adjusts the internal diameter of the exhaust system to suit engine revs and ensures good low to mid-range performance for a linear power output all the way to the rev limiter.

 

Later in the article there is a photo with the caption ...

Electronically controlled motor adjusts flap in exhaust, via cable, for maximum performance at all revs.

 

Remember the HP2 Sport? It was the introduction of the camhead valve design in a bike that sold for $11K more than the R1200S on which it was based.

clip--

From the 2/2008 issue of BMW Motorcycle Magazine in its article on the introduction of the HP2 Sport ...

 

An exhaust flap in front of the muffler is actuated by an electronically controlled servomoter via a cable. This constantly adjusts the internal diameter of the exhaust system to suit engine revs and ensures good low to mid-range performance for a linear power output all the way to the rev limiter.

 

Later in the article there is a photo with the caption ...

Electronically controlled motor adjusts flap in exhaust, via cable, for maximum performance at all revs.

--clip

 

Evening lkchris

 

 

So why would they want a smaller diameter pipe (restriction) at any point in the RPM range? (obviously not for more power so it must be noise control)

 

That statement is obviously a marketing ploy to put a positive spin on a needed noise reduction device.

 

 

I remember when the new (at that time) camhead RT was tested by Motorcycle Consumer News. They posted dyno charts of the new engine compared with the previous RT ('05-'09). I remember being disappointed in seeing they were virtually identical- and the later engine made slightly LESS peak power.

 

Frank

Edited July 18, 2014 by duckbubbles

I remember when the new (at that time) camhead RT was tested by Motorcycle Consumer News. They posted dyno charts of the new engine compared with the previous RT ('05-'09). I remember being disappointed in seeing they were virtually identical- and the later engine made slightly LESS peak power.

 

Frank

 

As if dyno hp figures mean anything in the real world.

 

My camhead runs way better than my previous hexhead ... which I thought was gutless.

 

Dirtrider, it's called "exhaust tuning" a concept I bet you've heard of. Pretty clever of BMW to do it on the fly. Pretty crude and uneducated to remove it.

 

Edited July 20, 2014 by lkchris

My camhead runs way better than my previous hexhead ... which I thought was gutless.

 

There's definitely been a clear straight line of motor improvement from my oilhead to my hexhead to my camhead. Not just power but drivability.

 

Dirtrider, it's called "exhaust tuning" a concept I bet you've heard of. Pretty clever of BMW to do it on the fly. Pretty crude and uneducated to remove it.

 

You know, I have heard of exhaust tuning, I just don't see how adding an exhaust flapper valve restriction adds power though.

 

I have heard of added exhaust restriction adding exhaust noise control though.

I remember when the new (at that time) camhead RT was tested by Motorcycle Consumer News. They posted dyno charts of the new engine compared with the previous RT ('05-'09). I remember being disappointed in seeing they were virtually identical- and the later engine made slightly LESS peak power.

 

Frank

 

As if dyno hp figures mean anything in the real world.

My camhead runs way better than my previous hexhead ... which I thought was gutless.

Don't get me wrong, I agree that the camhead engine is stronger than the hexhead. My RT is just as "seat of the pants" fast as the ST was- and it weighs a bunch more. I would think it would show up on a dyno as well. I wouldn't have called my ST "gutless" but I know I hit the rev limiter a lot more on it than I have on the RT.

 

Frank

You know, I have heard of exhaust tuning, I just don't see how adding an exhaust flapper valve restriction adds power though.

 

I have heard of added exhaust restriction adding exhaust noise control though.

At lower rpm engines generally benefit from greater back-pressure and different timing of the reversionary waves that help with cylinder filling. The butterfly allows the same exhaust to act like a low end-tuned pipe at low rpm and to be a more free-flowing exhaust at high rpm when you want to be getting as much gas down the pipe as possible.

 

The butterfly valve is not any significant restriction on full flow when fully open (as you can see looking through the valve), so the valve does not "take away" any performance on top -- in fact, it probably *increases* top end performance by allowing the pipe to be large/more free-flowing than a fixed pipe because the pipe does not have to be compromised to ensure adequate performance on the low end.

 

So, as good or better top end power, and *increased* low end torque that is obtained when the valve is operated to create more back-pressure -- a win-win in my book. No way I'm taking it off my camhead.

Afternoon Mark

 

I haven't ever seen or found any information that adding exhaust backpressure is beneficial to power.

 

Obviously working with pipe diameters/tapers & other reversion inhibitors could be very beneficial to kill exhaust reversion (especially with long duration cams). As rule the cat. converter is very good reversion killer though so needing a valve restriction doesn't make much sense on a cat equipped vehicle.

 

On the other hand I could see smaller diameter (possibly longer) pipe somewhat increasing low & mid range torque but that is smooth flowing & could alter reversion. A flapper valve in a larger diameter pipe is very suspect for anything but noise control.

 

I have seen a lot of exhaust flapper type systems on production automobiles & every one I have seen so far has been for noise control or acoustics altering in some form or another.

 

 

 

 

The collector is the point of reflection due to diameter change. With the valve being after the collector, I cannot image it could have any significant affect on the wave timing. Being after the catalytic converter can't help either.

Didn't Yamaha have that for a while on their big bore sports bikes, X-up, or something like that also Honda. Constantly tuned the exhaust as I recall.

 

Yep, found this ... http://en.wikipedia.org/wiki/Four-stroke_power_valve_system

Edited July 25, 2014 by bwpsg42

Morning bwpsg42

 

That is a thought. A Helmholtz system requires some form of expansion area or added chamber to function. (you see that on some modern automobiles with a second muffler or resonator but no outlet on that side). Some of these Helmholtz systems are passive (always active) & some do have a control valve to tune the active RPM or load range.

 

On most automobile systems these Helmholtz resonators are strictly for noise attenuation or exhaust noise tuning (no real power gain unless you figure in that using that extra tuning chamber allows using a less restrictive muffler & higher flowing exhaust system but still meeting exhaust noise emission laws).

 

By looking at the newer BMW boxers with that exhaust flapper valve it is obvious that there is no added muffler or added chamber for Helmholtz effect so that is quickly ruled out at face value (at least it was by me).

 

From your link it does appear that a few other motorcycles are using some form of Helmholtz resonation for one reason or another. I would imagine the main reason is for noise pass-by (vehicle noise emissions) as most of these systems have appeared since the more stringent noise emission laws have gone into effect.

 

But your link made me look a little closer-- I couldn't get past the noise only thing as there just isn't an obvious added chamber for the Helmholtz resonation effect to work.

 

That is UNTIL a little bell went off in my head, the motorcycle systems seem to be on multi cylinder motorcycles with odd or opposed firing orders. Cha-Ching-- It appears that there might be a little Helmholtz effect available by using the cat. & the non firing cylinder pipes for the resonance chamber(s).

 

I seriously doubt the gain is much but maybe just enough to measure or advertise on (I still believe the main reason for that expensive valve & control programming is noise control but there is the possibility of a very slight exhaust wave tuning due to the forward pipe & cat volume.

 

 

I wont pretend to understand the wiki-article or your informed discussion. I was just trying to say that it's not something new. In 91 a friend had a liter Yamaha sport bike and I rode it a couple times. Coming off my R100 it just blew my mind and I recall him going on and on about this system. It had nothing to do with the valve I suspect, but the power and acceleration compared to the R-RS was a watershed moment. The next year I bought a 907ie., a wonderful bike that I shoot myself daily for trading a couple years later for a 900SS.

 

Thanks for the info, I will have to read more about the technical stuff now.

Research the "Flapper valve" subject at ADV Rider and or UKGSer.

Folks posted explanations with dyno charts how this flapper valve works.

Nothing to do with noise levels...in fact the newer bikes tend to be much louder.

I had an EXUP equipped Yamaha FZR1000 back in 1994 and I remember the salesman telling me explicity that the EXUP was there to boost low and midrange power as well as cut noise.

All I can tell you from the seat of the pants, that bike was grunty at low revs and really wailed up top. I think Yamaha claimed 145HP and getting off the lardy K1100RS it was a real powerhouse. It wasn't quite up to the 91 GSXR1100 I had owned previously (for bottom end power) the oil cooled GSXR didn't have any flapper valve though and was probably an unfair comparison with bigger capacity and Suzuki know how.

I finally sold the FZR1000 in 2006 and was one of the most reliable, fun bikes I ever owned.

 

Teddy

"Actuated with an electric servomotor and opening and closing cables, the exhaust system generates a particularly sonorous flat twin sound that also conforms to the applicable laws."

Quote from BMW Motorrad .com tech page....

I think the clue from the wiki article is "more linear power output" one of the things I noticed when I first rode the bike was the wide power band. It also sounds very cool at 80mph when you wind the throttle :-)

Hi - I removed the flapper valve and used the replacement pipe from Wunderlich they sell & it fits perfectly. No computer problems either.

 

At the same time I put on a K&N filter (for re-usability, not power) & the BWM AF-XiED.

 

With the flapper removed, the K&N and the AF-XiED, I fluked-out and found a great combination/mod - the bike now runs very smooth and strong.

 

Also pulling away from a stop light in first gear is defiantly more seamless or smoother, not sure if the words describe it properly, but it is easier to get going from a stop.

 

In addition I can now roll on in 2nd & 3rd gear and pull away from my buddy's new Triumph Trophy and pull away pretty fast from other stock Camheads.

 

Hope this helps.

 

2012 R1200RT 34K KM, AF-XiED set at seven for both sides.

Is the flapper valve related to the back pressure? I want to remove the muffler just for making the bike louder but don't want the bike to run leaner! Will disconnecting the O2 sensors make the bike richer? The bike already has a K&N filter installed so there's more air in the intake that contributes to making the bike leaner.

Afternoon Zapata]

 

Is the flapper valve related to the back pressure?--Yes, but that is not it's primary intended purpose. The flapper valve is mostly an exhaust noise modifier so the bike can pass noise pass-by emission.

 

I want to remove the muffler just for making the bike louder but don't want the bike to run leaner! --For most riding situations the o2 sensor will keep the engine from running leaner. If you remove BOTH the muffler & the flapper valve THEN you could end up with an exhaust reversion situation & THAT can effect smooth engine operation.

 

Will disconnecting the O2 sensors make the bike richer?--Not normally, it CAN effect both leaner & richer operation depending on the engine load, RPM, & part of the fueling map in play. Do not disconnect the o2 sensors & remove the muffler as that can cause a lean condition in some operating ranges.

 

The bike already has a K&N filter installed so there's more air in the intake that contributes to making the bike leaner-- How do you know that there is more air in the intake? The main intake restriction is not the air filter element it is the rather small air filter box snorkel inlet.

 

I remove the muffler and install an exhaust tip. I am putting the stock muffler back and will wait to get the Remus or Akrapovic. The sound in the video does not compare to the loudness of the live sound but I can detect some backfiring and hesitation when rolling the gas.

 

I remove the muffler and install an exhaust tip. I am putting the stock muffler back and will wait to get the Remus or Akrapovic. The sound in the video does not compare to the loudness of the live sound but I can detect some backfiring and hesitation when rolling the gas.

 

 

Afternoon Zapata

 

That is pretty typical of the 360° 2 cylinder BMW boxer. They just don't sound great with an open exhaust due to the 360° firing order.

 

I remove the muffler and install an exhaust tip. I am putting the stock muffler back and will wait to get the Remus or Akrapovic. The sound in the video does not compare to the loudness of the live sound but I can detect some backfiring and hesitation when rolling the gas.

 

 

Afternoon Zapata

 

That is pretty typical of the 360° 2 cylinder BMW boxer. They just don't sound great with an open exhaust due to the 360° firing order.

 

+1 on the unsatisfying sound. It will always be sort of drone. It will never sound Hawg awesome.

I remove the muffler and install an exhaust tip. I am putting the stock muffler back and will wait to get the Remus or Akrapovic. The sound in the video does not compare to the loudness of the live sound but I can detect some backfiring and hesitation when rolling the gas.

 

 

Ebay has one. AKRAPOVIC plug and play.

Ebay item # 401490671633

https://m.ebay.com/itm/Akrapovic-BMW-R1200RT-ST-10-11-Street-Legal-Slip-On-Exhaust/401490671633?epid=171196891

BMW approved and it's cheaper than the identical one for $1,200 at the dealer.

Edited February 25, 2018 by 6speedTi