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.

 

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.

 

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...

 

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!

 

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.

 

In one particular machine that I have miles of personal experience with, the secondary throttles' opening curve WAS remapped in later editions to preclude taking them out for good throttle response. And even the new editions have no exhaust flapper. They do, however, have mufflers the size of howitzers.

 

Hello Fellows,

I just want to ask a straight question, "is it safe " to remove the exhaust servo, for the engine? I don't mind about the difference in low RPM (as some mentioned). But real question is, it is for the sound regulations or has something to do with the engine's long life (for sure I want/will hit more than 100k with it). I will not remove the cat. I only replaced the end muffler for SC Project.

 

It's perfectly safe to remove the servo. Just be sure to dongle its connector (Healtech Servo Eliminator).

I can't say I've noticed any loss of torque on either my Evo or GT, but considering how much they produce and me not being on a race track, who cares. The Evo also has an SC-Projects CRT can and a flashed ECU. The thing is sublime on the roads I use (Japanese twisties).

 

It's for sound attenuation at 5500 rpm, where the EU takes it's noise level tests. Until someone does the dyno test that refutes this, I'm going with zero performance difference with the flapper operating or not. Or removed or not.

I saw an SDGT with over 100K miles on the clock on Cycle Trader. No notation on whether or not the flapper contributed to the high mileage. I don't think it had anything to do with it.

 

1290's are about the last engine that would need a torque enhancing component, esp. one that has proven to be such a nuisance in normal use.

 

My take is, that if there was no noise restriction rules and testing at 5500 revs, there would be no exhaust valve. But what dose the exhaust valve do for the CAT its self, dose it help increase heat and total incineration of exhaust gases?. Don't no, but on both my euro 5 bikes, 2020 1290 and 2021 950 Multi, ive removed both exhaust valves, noticed no dip or difference in power. On my Multi, the valve stayed closed from idle to 5500 revs aprox, but it also had a 25mm bypass pipe around the exhaust valve, so never got completely choked to death. Obviously with the valve as part of the stock bike system for E5, there is some tuning to suit it, but because the bike is tuneable for and open system, its not a valve timing setup, more fuel related.