So, you have a BMW motorcycle and are interested in what the exhaust servo and/or balance pipe?
Great, first check out our other article explaining the basics of the exhaust servo/valve system used here.
Now that you’ve got the basics, lets talk about BMW specifically.
BMW motorcycles in general are very similar to the other models but with a couple important exceptions. First, and biggest, is the S1000RR (and HP4) uses TWO servo motors instead of one. The first one controls a valve in the header, referred to as the Balance Pipe. The purpose here is to regulate exhaust gas flowing through the header to balance the #2 and #3 cylinders exhaust gas pressure, presumably to increase torque in the midrange. The second servo motor is more traditional in that it is further back in the exhaust system, all other models just use the single, traditional servo motor setup.
If you happen to have an S1000RR or HP4 and decide to put in an aftermarket exhaust system you may run into some issues depending on what type of exhaust system you put on, either one or both of the servo motors will no longer be needed depending if you replace the stock header or not (fully system vs slip-on exhaust). Each Servo motor that you replace would need a Servo Buddy to replace it in order to prevent the bike from throwing codes. (21FA21, 21FA22, 21FA23, etc). (NOTE: HP4 will not illuminate the dash light for these codes, simply stores them, if stored codes don’t bother you, you do not need a Servo Buddy, just make note of the codes and ignore them in the future).
What’s “cool” about BMW servo motors?
Now fair warning, nothing in this paragraph is important to you, the user, but it is somewhat interesting in our opinion and we’ve included it here for the techies. It’s not often that we find unique technology in the powersport market, usually all the manufactures do basically the same thing and buy many of the same parts to assemble their bikes. However, BMW is unique as far as we can tell with their Servo Motors. While other brands use an analog system, using the ECU to apply direct power to a motor and reading position back via a separate yet integrated sensor, BMW did things differently. BMW provides static power to the Servo motor and then communicates digitally with the ECU to send requested position and the servo motor responds with current position. The servo motor will decide on it’s own when to turn it’s internal motor based on requests from the ECU. This setup allows for a lot more error checking and makes the BMW far more “intelligent” than the other brands. This also means it’s far more difficult to fool, but with our latest Servo Buddy for BMW motorcycles (PN: 42-2755) we have managed to use advanced microprocessor techniques to come up with a perfect solution, allowing our Servo Buddy to exactly mimic a working factory servo motor and valve system, at a fraction the size and weight with far superior reliability.
What about my model?
Have a BMW motorcycle and need a Servo Buddy? Great, we’ve probably got you covered, but if your model is not yet listed in our application chart please email us and we’ll be happy to help you out and maybe work together on validating your model/year. Check our official application chart for the current validated models here.