Exhaust flap valve

[Alan R]

A question of mere curiosity for r1300gs owners: does the exhaust have an exhaust flap valve similar to 1200/1250 models?
I ask this as I have f850gs and a r1250gs, the former has a humongous exhaust collector box but no flap valve, the latter has a flap valve but no collector box.
I understand that r1300gs bike have a collector box similar to the f850gs, hence my question. I wonder why some bikes have the flap valve but not others?
Alan R

 

[botus]

if you have shift cam you can control the fuel and air falling out the open exhaust valve - due to valve overlap - correctly using VVT
a flap valve is a budget half arsed way to partially do the same, and try and shut up the racket of a noisy exhaust

they did it to better manage emissions, rather than give a better power curve

 

[Alan R]

Thank you for your reply although I believe that you have somewhat confused the point of my question. I know of several manufacturers who use such a valve - who do not employ variable valve timing, indeed BMW used them on several r1200 iterations. My questions remain:-
1. Do r1300gs bikes have a flap valve?
2. Why do some models have a flap valve and others do not?
Alan R

 

[botus]

re questions - I answered much of it but you didn't get the explanation

1) can't confirm but there is no need for the flap valve on the shift cam bikes
2) I addressed point 2 in my original post

the more power you want, the more revs you have to play with, which means to get it to run correctly to make the big power, there is a longer time-frame where the engine has to have BOTH the inlet and exhaust valves open at the same time (its called valve overlap). this overlap means less low and mid-range torque and vastly higher undesirable emissions at the point the testing cares about - VVT can better manage the mess, rather than trying with a budget restriction in the exhaust...

VVT is vastly more complex and costly - but also a vastly better solution

re curves before 5000 rpm, the shift cam bikes make serious power where the 1200LC is a moped (that struggles to hold a stable load at 2-3K rpm hence no readings)
and yet the shift cam bikes can also rip it at the top end
and the 1300 manages a better torque curve everywhere, I guess because it breathes better at high revs with its shorter stroke

 

[Alan R]

Thank you again for your reply. A very technical answer that I feel again misses the point of my questions by discussing variable valve timing.
My f850gs doesn’t have a flap valve. My r1200gs hexhead had one, my r1200gs had one and my r1250gs has one too. I believe most HD’s have them too. It seems to be common knowledge that the primary purpose of the flap valve is to reduce noise, so does the humongous exhaust collector on a r1300gs render an exhaust flap valve redundant?
So, does anyone know if r1300gs bikes have them?
Alan R

 

[pbbanks]

Thank you again for your reply. A very technical answer that I feel again misses the point of my questions by discussing variable valve timing.
My f850gs doesn’t have a flap valve. My r1200gs hexhead had one, my r1200gs had one and my r1250gs has one too. I believe most HD’s have them too. It seems to be common knowledge that the primary purpose of the flap valve is to reduce noise, so does the humongous exhaust collector on a r1300gs render an exhaust flap valve redundant?
So, does anyone know if r1300gs bikes have them?
Alan R

Yes, the 1300gs still has an exhaust flap valve before the rear can. It closes shortly after starting to reduce noise when idling, eg stopped in traffic.

 

[MrC99]

A quick Google threw up this. So yes.

Edit: Apols as I see @pbbanks beat me to it!

 

[Alan R]

Yes, the 1300gs still has an exhaust flap valve before the rear can. It closes shortly after starting to reduce noise when idling, eg stopped in traffic.

Thank you. This is the same behaviour experienced with my r1250gs. I’m beginning to think that exhaust flap valves are only fitted to some large cc twins for noise reduction of big pistons at idle revs.
Alan R

 

[MrC99]

They're not unique to BMW bikes either. I think that some KTMs have them, as well as a number of different car makes & models. Lots of thoughts on various forums on why they exist including noise reduction, catalyst performance, back pressure, etc, etc... I was riding behind a fairly new BMW car recently and could see that only one of its twin exhausts had a butterfly valve fitted.

 

[TaskMule]

The real reason for this valve explained by someone who does the research

 

[botus]

Thank you again for your reply. A very technical answer that I feel again misses the point of my questions by discussing variable valve timing.
My f850gs doesn’t have a flap valve. My r1200gs hexhead had one, my r1200gs had one and my r1250gs has one too. I believe most HD’s have them too. It seems to be common knowledge that the primary purpose of the flap valve is to reduce noise, so does the humongous exhaust collector on a r1300gs render an exhaust flap valve redundant?
So, does anyone know if r1300gs bikes have them?
Alan R

ah, but now we have moved from technical reasons to have a flap valve - at the time the 2010 GS got it they hadn't worked out a cost effective VVT they felt brought what they wanted - to the current need for children to have farty exhausts

most sports cars now have illegal noise levels - and a flap valve to pretend to pass the tests... it seems the play station generation can't cope with life if they don't have it...

but the actual reason they infect many vehicles with that rubbish today is all part of trying to ban personal transport (ICE vehicles) - the more noise and irritation they can bring, the faster they can lock you in your cell and make you pay to watch netflix - before the next pandemic brings the final cure they are currently coy about letting out of the bag

 

[Alan R]

The real reason for this valve explained by someone who does the research

Thank you for that. A comprehensive explanation. It doesn’t clear up the question as to why some bikes like my f850gs that has to meet the same noise emissions standard doesn’t need an exhaust flap valve. I’m thinking big pistons producing big bangs need the control whereas smaller pistons escape the need.
Alan R

 

[botus]

"the real benefit" of the stupid flap valves on CARS !!! and Bikes - its got bikers banned - we now have a ‘Special Noise Quality Zone’ (ZEPQA) created in 2023, banning motorcycles, quads and buggies throughout the year - making 80,000 hectares of the Pyrenees, between France, Spain and Andorra, inaccessible to motorcyclists

Motorcycles are banned from parts of the Pyrenees National Park - FEMA

FEMA - the international motorcycling community

www.femamotorcycling.eu

 

[Alan R]

Thank you for your contributions. Invaluable.
Alan R