Replace stock exhaust muffler with a Leo Vince
My first major mod was to install a Leo Vince X3 aluminum exhaust muffler, part # 3606.
Cost was $347 from TreMX.com.
The main problems with the OEM muffler were: the extreme heat put off by the catalytic converter, the huge size and weight, the restrictive airflow. The LV solved all of these, it does not have a cat in it and is much smaller. It is a well made unit. Being a bit less restrictive it is a bit louder but with the quietest insert I do not consider it loud, it just has a more healthy sound compared to stock -- it sounds like it *should* sound, very nice! ... and much MUCH cooler! I chose the Leo Vince as from what I've read it is much quieter than the Remus, Scorpion, or Staintune and much cheaper than Akrapovic. Here are a couple of YouTube movies where you can hear the sound on an XMoto and an XChallenge.
Here is a look at what came in the box:
To describe the 4 inserts provided, in terms of the length of the part of the insert that is internal to the muffler: there are 2 long and 2 short inserts. The longer ones are more restrictive hence quieter than the shorter ones. For each pair by length (e.g. the long pair), there is a "skinny" smaller diameter one (with no tube sticking out the back) and a "fat" larger diameter one (WITH the tube sticking out the back). The skinny one is more restrictive hence quieter than a fat one of the same length.
In addition I think the spark arrestor (SA) will not fit on the "fat" ones since they have the tube sticking out the back.
So you have these 4, and this is my guess at listing them in order from LESS Restrictive ("loudest, highest performance") to MORE Restrictive ("quietest, lowest performance"):
Short Fat
Short Skinny (optional SA)
Long Fat << installed from factory I believe
Long Skinny (optional SA)
Others have estimated the long ones give you better bottom end power and the short ones give you better peak horsepower. I installed the "Long Skinny" insert, with the spark arrestor. Per others suggestion I used anti-seize compound (hi temperature, like nickel based) when installing the stainless screws that hold the insert into the aluminum body.
Here is a comparison of the relative sizes of the Leo vs. the OEM muffler:
One of the issues with the BMW exhaust in general is that the exhaust header pipe has VERY LITTLE clearance from the coolant hose and some people have had their hose seared by the pipe: To help improve this clearance, after you remove the OEM muffler you can then loosen the 2 exhaust nuts at the head and rotate the header pipe to gain a bit of clearance, then retorque them.
Here are some before and after pictures of the clearance to the water hose, and of the overall look:
A fix for a potentially SERIOUS problem: Because of how the LV muffler is bolted onto the frame, it is only bolted in one place with a bolt mechanism that can rotate to fit into any position. The problem is, even if you apply blue threadlocker, riding off road can eventually cause this adjustable junction to rotate and let the muffler sag, in which case the exhaust header pipe can come close to searing the coolant hose.
My solution for this was to take a thick aluminum strap and bend it to fit around the rear tail rack bar (in my case, or a grab rail bar on a stock bike). Then I drilled a hole into it and slipped the exhaust bolt through it. This adds plenty of support. Also notice the use of a spacer to move the exhaust out a bit farther (to provide clearance away from the Wilbers shock reservoir I added later).
Finally, the small front heat shield was a bit of an annoyance as it stuck out so far it rubbed against your left calf, especially with full riding boots on. In addition, the heads of the screws that hold the heat shield on were digging into my leg.
My fix was to bend the brackets in a bit, and to use stainless flat head screws instead, which have a lower profile. Plus to minimize the heat further I put some hi-temp black silicone RTV (Permatex Ultra Black) over the heads of the screws (which helps mainly when riding in shorts :). I also installed exhaust heat wrap on the pipe (partly to lessen the heat on the Wilbers shock reservoir too).
Update after a year of use: The exhaust has not drooped since I added the extra strap to hold it in place. Also, I recently had to pass a 96db sound check at the Moose Run rally and it measured 93 after a year old (with the quietest inserts), this was at 4000 rpm and holding the db meter roughly a foot away from the exhaust. The spec from LV for the quieter (long) inserts is 94db.