[Hammerhead]

I imagine any dyno testing may show a different result between just dongled and removed completely as their reply indicates dongling instances are occurring in conjunction with other mods, such as freer flowing exhaust and intake, fueling mods etc. MIne came about after the servo motor ceased functioning. As the conventional wisdom of the time indicated, it's a noise abatement device and as we all know, the catbox muffles more than the muffler. So....
Stage 1 Servo disconnected and dongled but not removed. Flapper left in the pipe.
Stage 2 Flapper removed, along with it's cables and servo. Slight weight loss
Stage 3 Dongle and cat delete More weight lost

There has been debate about the ECU adapting enough to a cat delete to make fueling mods unnecessary but still possibly desirable.

 

[Spartacus]

It would be good for someone/anyone to come up with the dyno comparison mentioned. I for one would like to see this. As for butt dyno's - they can't be trusted. I used to port heads for a few bike shops and got to know them, a good buddy with a Harley dealership had the towns first and only dyno.
Way more than once a paying dyno customer (mostly Jap bikes) would come in with the latest and greatest in modifications. Some were outwardly hostile to the poor guy running the dyno when the expected results didn't come in. They were certain there was an extra 50HP in there somewhere! A few times the result was worse than where they began.

Getting back to servo's, flapper valves and backflow, there are events going on here that we don't understand.
My experience with exhaust has always been "to get more HP ... open it up". Two strokes are another matter.

 

[Hammerhead]

Exhaust tuning used to be a matter of sliding the megaphone back and forth on the pipe to get the powerband at a certain rpm.
It's been demonstrated that the only advantage of an aftermarket exhaust system is lighter weight. They knew what they were doing where they made these Beasts.

If opening them up is advantageous, an obstruction along the way is counter-intuitive. I always thought pulling the secondaries on my ZX-14 was as much about removing an unnecessary obstruction as it was getting a direct throttle response.

 

[nosurrenda]

Removing the secondary throttles (2T) on GSXR's is very common, and those who do it swear by the 'improvement' to throttle smoothness and improved top end power. So again, using Woolich, I once flashed my GSXRs ECU and disabled the 2T so it remained 100% open in each gear and all throttle positions. With back to back rides, the motor definitely felt smoother, but there was a noticeable loss of pull from low down in the revs, similar to when I disabled the exhaust servo. I don't know it it unleashed more power overall but it seemed to come on a bit harder in the upper end. I've since concluded that the Suzuki engineers knew what they were doing when they designed and tuned these servos in their ongoing pursuit of efficiency and street usability. I suspect that KTM's engineers are similarly knowledgeable.

 

[CUL8R]

The akra system was made in conjunction with KTM engineers and they did not include an
exhaust valve in the system and it makes more torque through out the power band and more
horsepower but it is also for race use only. KTM is forced to use a CAT and an exhaust valve
to make the bike street legal and they tuned it to work the best it can with them installed.

 

[cors187]

Big bore exhausts can benefit by what I call variable flow valving ... But to see it work for the whole range and for all riding styles we need smart tech ....
Hammy and has a point ,the relief is somewhat important ...
The tip of the 4 stroke exhaust can be used for tuning if the rest of the exhaust doesn't cancel it out (technical)........ The flap can be used for good effect if it can be tuned , but I think the flap is used in conjunction with choppy throttle riding styles, what about race type throttle usage ...

 

[NickDipples]

The exhaust servo is STRICTLY for noise compliance for Euro 4/Euro 5 machines and will have no/a negligible effect on torque. Look at the emissions testings requirements for the sound levels and the RPM levels at which they test for noise, and look at any dynograph for any modern bike and you'll see the link for why the servo on any modern bike works.

If your argument is that the motorbike benefits from 'back pressure' provided by an exhaust servo, you don't understand the fundamentals of your argument.

 

[cors187]

i thought that vid helps the pro flap case?

 

[nosurrenda]

The exhaust servo is STRICTLY for noise compliance for Euro 4/Euro 5 machines...If your argument is that the motorbike benefits from 'back pressure' provided by an exhaust servo, you don't understand the fundamentals of your argument.

Sorry friend, but I think it is you who misunderstands. This is not about 'back pressure' but 'exhaust scavenging'. The flapper opens at different ratios depending on throttle position and gear, which has very little to do with noise compliance and directly impacts on low end torque. I've proven to myself how this works using back to back flashes on my superbike. But if you want to mod your bike with an open system and all the other mods that go with, please do so and enjoy. Your money, your bike. Hmmm, think I'll buy that carbon front fender I've been eyeing off.

 

[Spartacus]

Think the pro flapper crew needs to go back and re-listen to the first 2 minutes plus. I know the exhaust valve is 15% smaller in every case in every engine (no exceptions) to speed up the scavenging process and also because there is no weight to the burnt gasses while being physically pushed out. There are accepted engine engineering rules, this is why you do not see larger exhaust valves (hurts torque). The flapper is part of a very precise noise abatement regime and nothing else. The factory does an excellent, maybe superb job of engine management with flappers. However the race only engine they build has no use of ANY of this tech. In a racing engine, if it was useful it would be there.

 

[nosurrenda]

In a racing engine, if it was useful it would be there.

Another misunderstanding. Race engines do not require flappers because they spend all their life in the upper half of the rev band going round and round and round a track. So race engines don't benefit from low RPM torque, and a flapper would be a mere waster of space and weight. Remember, they only work in low RPM via exhaust scavenging. Above 5000rpm or so (on a bike) they're wide open so as to not obstruct the exhaust, and yes in those lower RPM they also reduce noise output. Compared to a race engine, street engines do benefit from low end torque because most of the time is spent in the lower half of the rev band, which is why the flapper's there. Yet again I will state that I have the benefit of a flash tuner and can do back to back rides with a noticeable (that is, significant) reduction in low end torque once the flapper is disabled. With my (L6) GSXR 1000 the exhaust valve was advertised as a factor for it's low down grunt, which for a superbike is actually really bloody good. Yamaha, if I recall, used to make the same claims with the Exup system. Perhaps the effect is more noticeable on an inline 4 compared to a big bore twin.

 

[CUL8R]

 

[cors187]

awww

these effects are purely signal related........ we cant be caught thinking that within a large system ,that either the intake throttle gap or exhaust throttle gap expanding or shrinking doesn't effect drive-ability.
Drive-ability is throttle response.

I think without the discussion suggesting more power, this is a simple phenomenon of efficiency.......School students could show it using variable intake and exhaust gaps .

 

[cors187]

I felt the torque seems more “linear” and didn’t seem to have that low to midrange punch

Could it be better driveability in that specific area when the intake and flapper effect each other , when the cats and head valves do not play any part in the vacuum dance. You might have more supporters ...

 

[ilmothefinn]

It is a never ending debate... But one thing is at least sure for me. The old 2014 sdr was very nice and smooth from factory and I let the marketing people persuade me to decat, dyno-tune and remove the SAS system (actually the exhaust popping after decatting was not what I liked). I justified the loss of money and small increase in top HP with the fact that the bike became more interesting to ride. It was much more straightforward and needed more attention of the rider...

But, time flyes and I got old (don't know about the wife). Traded the old bikes and had 2021 SDR:s which are so smooth and wonderful - I think I just enjoy the riding and do not use so much high speeds. Not yet anyhow (never say never, some people become crazy when they get old!). It is perfect for that purpose, at least for me! My wife has the same opinion, she has another 2021 SDR (earlier she had a 2015). We couldn't care less what people say they are meant for in their little minds, we just like them as they are (in our little minds).

Had a remote mic under the seat for last ride and there is some sound question anyhow - but low noise level is good, we have somehow started to not like a lot of noise anymore. SDR is not the best sounding bike one could say.

 

[NickDipples]

Sorry friend, but I think it is you who misunderstands. This is not about 'back pressure' but 'exhaust scavenging'. The flapper opens at different ratios depending on throttle position and gear, which has very little to do with noise compliance and directly impacts on low end torque. I've proven to myself how this works using back to back flashes on my superbike. But if you want to mod your bike with an open system and all the other mods that go with, please do so and enjoy. Your money, your bike. Hmmm, think I'll buy that carbon front fender I've been eyeing off.

Exhaust scavenging and back pressure are two completely different concepts; way to bring up a red herring. Exhaust servos are ONLY there to get bikes through UNECE noise regulations (Regulation 41), which tests bikes while stationary, and at multiple speeds up to WOT at a final speed of 50kmh. You can read the testing procedures here and see why any modern motorcycle has the exhaust servo closed at the exact ranges that would apply for the testing:

https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R041r2e.pdf

 

[Hammerhead]

I think if motorcycles benefitted performance-wise from flappers, they would have been included in some form or other long before the last few noise-regulated years. Anti-inversion exhausts, flattened port and pipe shapes (ever see the ones that look like Cobras about to strike?), every sort of exhaust trickery has been tried, which is why the magazine testers were able to illustrate that aftermarket exhaust yielded no power or torque advantages over stock. You can change the note and lose some weight and that's it. And secondary throttles exist to flatten and smooth (delay) throttle response and have nothing to do with intake tuning other than being an obstruction on the opposite end from flappers. Noise and speed restrictions are the products of regulation not performance tuning.

 

[ilmothefinn]

I might be wrong but I think there were no noise regulations in 1987 when the first exup (or any kind of 4-stroke exhaust power valve system)
was in a motorcycle? Maybe there were some (regulations) in California?

Another thing is that the noise is sometimes important, my wife says she likes to hear the engine rpm so there is no need to look at the rev counter while riding - which is sort of important too if one would have limited hearing for some reason. I had noisy cars in younger years mostly with manual transmission and the first quiet one was luckily automatic... Kind of weird like it is now with the very quiet SDR.

Silence is golden, they say and I somehow believe it is true. We had a summer cottage at a place where sometimes it was so quiet you began to hear blood circulating in your ears. It was nice and fun!

 

[Hammerhead]

An EXUP is quite a bit more than just a flapper. It's a series of valves in an enclosed chamber
designed to vary the volume of the chamber. The can was as big as a catbox. Obviously no room for that anymore.

 

[cors187]

And secondary throttles exist to flatten and smooth (delay) throttle response and have nothing to do with intake tuning

Well to be fair to the inventor of said obstruction ... The secondary throttles can be mapped to reduce the effect of giving the motor to much throttle at too low revs .... In the adventure /Enduro world you might find a very predictable and tourqy cable driven motor.. High revs /wot , I agree with the consensus ....

What's wrong with fine tuning the 4 strokes using the exit tip...

The flapper on the 1290 probably and I would say quite predictable phenomenon where certain revs using certain throttle creates certain outcome...

Actually now that I think of it , it would be stupid of ktm too not try and tune this noise reducing flapper to benefit the road use .......
saying that ktm inserted the noise flapper and didn't try to integrate it sounds a bit off...