I have a 2015 650 LT. The bike has 300 miles on it and have a few questions I hope some one can answer.
I am upgrading the exhaust with a full system. Most likely the Two Brothers or Scorpion. I was told I do not need a power commander. True or False? If not needed would I gain anything from it?
I'm assuming changing the exhaust would void the factory warranty as well.
Modern engines are a combination of weak closed loop control and open loop control. Even the open loop bit generally has some closed loopiness to it as it gets feedback from the MAP sensor.
In the closed loop, the O2 sensors feedback info and the fueling will be adjusted to some degree, keeping the bike at generally the same air-fuel ratio for minor changes like a pipe.
In open loop operation, there's still some adjustment based on MAP input, but it's more of a fixed shot of fuel for a given throttle position/rpm.
So what happens when you do things like change a pipe or air filter? It allows more air to flow thru the engine. If you have a fixed shot of fuel in the open loop mode, that means you'll have more air than stock and the engine will run leaner.
Running lean is nice in that it maximizes fuel efficiency. OTOH, it takes away power and causes the engine to run hot. Heat kills mechanical things...really all things.
Is the heat going to be enough to kill the bike in the time you own it, probably not. Might it cause you discomfort? Perhaps.
Generally, bikes are mapped richer in the open loop areas of the map, so a small change in airflow from a pipe probably isn't going to hurt much. Environmental agencies test vehicles at conditions where they run in closed loop. That's how companies get away with running richer in the open loop areas of the map.
Having said all this, it also depends on your taste of things like throttle control. Many bikes are so lean stock that they have very lurchy response and often surge at steady throttle. I personally hate a lurchy throttle and have a PC-V on my otherwise stock bike for no other reason than to fix that issue. I have the liter version. Don't know if it's lil bro suffers the same lurchiness or not.