Exhaust valve is a very specific part; you’d have thought an engineer might have known the difference
He’s an electrical engineer.....
Exhaust valve, poor cold starting 1200
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He’s an electrical engineer.....
Electronics you heathen
Soz....
A fascinating subject and none of us here have a complete understanding of what this flappy thing does
Thats not true, we know it flaps around and sometimes it gets stuck so doesn’t flap around
I'll forgive you just this once
Could you pleas elaborate please. I don't quite understand the question. (Remember, I'm a foreigner
Every exhaust is a compromise size wise. Altering its length or bore has a bearing on gains or losses at different parts of the Rev range. So no one size or length is ideal across the board.
Exup ( Yamaha) h-Tev ( Honda) and set ( Suzuki) all use a flap to alter the volume of the exhaust in line with different rpm to try and overcome this limitation.
They all went about it slightly differently but essentially the aim is to alter the back pressure acting on the motor to suit different revs.
Interestingly I read that 600cc Yamaha’s in Europe didn’t get it but in the USA which had stricter emissions regs in states like Cali, they fitted it as they found it reduced emissions.
I honestly could not say for sure.
However, whenever the exhaust flow gets disturbed, it will affect the operation in many ways.
In the Bosch information they debated using a flap to influence the flow of the exhaust, but it was more of a emission point of view rather than performance. If this is the German way of explaining the same effect that the japanese engineers where trying to obtain will remain unclear.
However, when googling the different flap systems. I get the most hits from devices made to help out removing the flap valves.
Sometimes the engineers get so occupied by their calculations that the forget the result. These systems seemed to be the 'Hot' way of doing things 20 - 30 years ago, while there seems to be little talk about it now.
I guess it would make a very complicated algorithm if you try to use the flap for several different chores simultaneously.
Might be a dead end then. Manufacturers seem to come at the same thing from a different angle now or use a mix. I know Honda and Ktm are using airbox flap devices now as are Aprilia. Presumably to control volume or flow to influence the cylinder in a similar way to scavenging. Below is the Aprilia blurb on it taken from their service portal.
Just checked my V5 document, Noise 93dBA at 3875 rpm, at these revs the flap is wide open, so can't be reducing the noise.
Drive by test 75 dBA, but no conditions specified, but of course we don't know what distance the microphone was placed, this is critical as sound pressure drops of hugely with distance.
Drive by test 75 dBA, but no conditions specified, but of course we don't know what distance the microphone was placed, this is critical as sound pressure drops of hugely with distance.
Sound test spec from FEMA.
The motorcycle enters the testing area with a fixed speed of 50 km/h, 10 meters before the microphones it starts full acceleration and 10 meters after the microphones the throttle is shut completely. During all this time the microphones register the sound, that should not exceed the limits mentioned above. Of course, gear and all other kind of variables and circumstances are described in detail. Next to the WOT test the motorcycle is also tested stationary with (in most cases) half of the maximum engine speed. The sound emission in dB(A) and the engine speed with which it was measured are mentioned on the VIN-plate (see picture) for enforcement
Can you point me to the documentation, I want to find out what the distance is to the microphone is for both the static and ride past test.
Source - www.fema-online.eu
The Wide Open Throttle test
The vehicle is coming from the left and follows the line C-C. In principle, he has a constant speed of 50 km/h, but he can drive at a lower speed and accelerate earlier, provided that the speed on the line A-A is exactly 50 km/h. When the front of the vehicle passes the line A-A, the throttle control shall be shifted to the maximum throttle position as rapidly as possible and kept in this position until the rear of the vehicle passes the B-B. At this moment the throttle control shall be shifted to the idle position as rapidly as possible. The microphones for the sound measurement are set at line P-P at 7.5 meters from line C-C. The full length of the test range is 40 meters. Within a radius of 50 meters measured from the centre of the acceleration area, no structures or other obstacles may be displayed which may reflect or affect the sound (shown with line R50). There are many other, highly detailed requirements for the test environment and the sound test itself.
The stationary sound test
The microphone is positioned obliquely behind the outlet at a distance of 50 centimeters in a 45-degree angle on the vehicle’s longitudinal axis. In the case of a vehicle with exhausts on both sides of the vehicle, two microphones are used, situated on both sides of the vehicle. The height at which the microphones are placed is equal to the highest point of the outlet of the silencer, but no less than 20 centimeters from the ground. The measurement is done with the gear in freewheel and at an engine speed which is half of the maximum. If the maximum engine speed is less than or equal to 5,000 rotations per minute, then it is measured at a speed that is 75% of the highest achievable engine speed. The free space around the tested vehicle is at least three meters on all sides.
Source - www.fema-online.eu
The Wide Open Throttle test
The vehicle is coming from the left and follows the line C-C. In principle, he has a constant speed of 50 km/h, but he can drive at a lower speed and accelerate earlier, provided that the speed on the line A-A is exactly 50 km/h. When the front of the vehicle passes the line A-A, the throttle control shall be shifted to the maximum throttle position as rapidly as possible and kept in this position until the rear of the vehicle passes the B-B. At this moment the throttle control shall be shifted to the idle position as rapidly as possible. The microphones for the sound measurement are set at line P-P at 7.5 meters from line C-C. The full length of the test range is 40 meters. Within a radius of 50 meters measured from the centre of the acceleration area, no structures or other obstacles may be displayed which may reflect or affect the sound (shown with line R50). There are many other, highly detailed requirements for the test environment and the sound test itself.
The stationary sound test
The microphone is positioned obliquely behind the outlet at a distance of 50 centimeters in a 45-degree angle on the vehicle’s longitudinal axis. In the case of a vehicle with exhausts on both sides of the vehicle, two microphones are used, situated on both sides of the vehicle. The height at which the microphones are placed is equal to the highest point of the outlet of the silencer, but no less than 20 centimeters from the ground. The measurement is done with the gear in freewheel and at an engine speed which is half of the maximum. If the maximum engine speed is less than or equal to 5,000 rotations per minute, then it is measured at a speed that is 75% of the highest achievable engine speed. The free space around the tested vehicle is at least three meters on all sides.
Thanks - looks interesting - as far as the static test goes, there is no way the flappy thing can help reduce the noise as it's wide open under those condition. For the drive by I have my doubts too, unless you kept the revs below 2,000 - but the devil is in the detail of allowed revs, if specified. I need to dig a bit deeper, I think they reference another document in that article.
Just looked at the reference eeeek, lots of bedtime reading here!!! UNECE Regulation 41
Hi. I think i have same or similar problem with my 1200gsa TU 2011. It starts, then drop the rpms and stall. I have to hold throttle for a bit on bit higher revs then it's ok. And not sure but idle feels a bit rough too.
Yep get the flappy valve before the silencer checked.
Well OK it's not a GS or even a BMW but my KTM 1290GT has/had one of those pesky exhaust flaps. I've had the bike for eight years and the only issue of any description with the bike was that occasionally, the flap would jam and the engine would go into limp-mode. Dealer said that the flap adds another baffle at predetermined revs, to help keep the noise down in built-up areas. An EU requirement.
My earlier GSA had a flap with similar sticking problems. I put up with that but certainly wouldn't again.
On the KTM I initially disabled the flap by removing the activation cables and immediately, the bike felt better in terms of smoothness and improved general riding experience. The sense that the engine was being strangled at certain revs disappeared immediately.
So off came the cat, incorporating the flap, the activation motor and cables. It was necessary to substitute everything taken off with a Healtech plug-in "Exhaust Valve Eliminator" to convince the ECU that the flap's still there and also a Remus link pipe, incorporating a mini-cat at about a quarter of the weight of the original.
I've had the mixture checked and it's fine. The ECU has adjusted itself sufficiently to cope with the new cat. Possibly, that wouldn't have been the case had the cat-free link pipe option been fitted.
So, if your flap's playing up, I suggest initially disconnecting the activation cables and see how you get on. The KTM is a massively powerful bike as stock but getting rid of all that EU flap crap has liberated the engine. The principles are presumably the same on both bikes. Just give it a try with the flap open and sod the Eurocrats!
My earlier GSA had a flap with similar sticking problems. I put up with that but certainly wouldn't again.
On the KTM I initially disabled the flap by removing the activation cables and immediately, the bike felt better in terms of smoothness and improved general riding experience. The sense that the engine was being strangled at certain revs disappeared immediately.
So off came the cat, incorporating the flap, the activation motor and cables. It was necessary to substitute everything taken off with a Healtech plug-in "Exhaust Valve Eliminator" to convince the ECU that the flap's still there and also a Remus link pipe, incorporating a mini-cat at about a quarter of the weight of the original.
I've had the mixture checked and it's fine. The ECU has adjusted itself sufficiently to cope with the new cat. Possibly, that wouldn't have been the case had the cat-free link pipe option been fitted.
So, if your flap's playing up, I suggest initially disconnecting the activation cables and see how you get on. The KTM is a massively powerful bike as stock but getting rid of all that EU flap crap has liberated the engine. The principles are presumably the same on both bikes. Just give it a try with the flap open and sod the Eurocrats!
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