I was reading up on how both my Ducati and various models of
Buell bikes have a servovalve in the exhaust header to tune the torque curve of the engine.

In studying the concept I came across this...

http://www.tabperformance.com/Reduce-Back-Pressure-Exhaust-s/203.htm

Is this simple mod a worthwhile thing to try on our thumpers?
Or just something that works with twins only?
Or total bull?

My personal interest is to learn about how exhaust effects the torque curve in order to decide on whether or not to machine my exhaust port and go with a bigger header.
But reading the above source got my attention, particularly the results reported:
Run 5: Had the lowest horsepower, but the 2500-4000 RPM power was the highest. This is the RPM band that most riders spend their time riding.

Run 6: Improves the 3000-4000 RPM horsepower drop over run 7 without any significant drop in maximum power.

Run 7: Makes the most power, but has a huge hole in the power band just above 3000 RPMs. Since the thumbscrew is parallel to the pipe in this case, it has a very small profile and would be very similar to it not being there at all

It gave me
This video does not exist

https://www.youtube.com/watch?v=KjKUKhHQLHg

I think the use of the words "back pressure" is a bit confusing.  The goal really isn't to create a restriction to the flow of gases - the goal is to break up the pressure waves that can flow back into the header pipe and create pulses on the back of the exhaust valve....at the wrong time.

The reason a muffler works is that the pressure wave reverses as it enters the muffler due to expansion into it's larger area, most of this negative wave returns to the exhaust valve just before it closes and pulls out the remaining exhaust gases and helps pull in a fresh charge(the intake valve is opening as the exhaust valve is closing -valve overlap) , this only happens because the header pipe is 32inches long which controls the timing of the wave , the rest of the wave travels out the pipe with the exhaust gases ,but it's ill timed reversal is blocked by the baffle in the muffler . With a straight pipe or a muffler with no baffle the wave must continue to the end of the pipe before reversing and at certain RPM will arrive at the exhaust valve as it's opening and imped complete removal of the exhaust gases and unburned fuel, this causes the mid  range sag you see in the video. Placing a bolt /baffle in the end of the pipe brakes up the wave ,but you lose performance over a muffler system.

The slinky is affected by the temperature of the exhaust gases ,as a larger header pipe has more surface area the gases in the header pipe cool more quickly ,this slows the returning wave ,which may make it arrive at the exhaust valve to late. this is why the largest exhaust pipe of 1.5 inches  ID is recommended .I would think a larger exhaust header could be used if it were made shorter.I believe the stock header is 32 " long, shorter headers favor higher RPMs, longer favor low or mid range,I believe the range for 650 cc motors runs between 30" and 34" ,Suzuki picked 32"to highlight mid range performance on the savage (logical).you should take care in opening the exhaust port ,Exhaust is pushed out ,and the "slinky" can be moving at nearly the speed of sound,opening the port too much could slow the gases inside the port and kill the flow through the head.