A look at the XR1200's Exhaust Cans
Drilling like this will not give a major sound increase, and obviously
does not lose any weight. And while, the drilled stock pipes that I have seemed to match the performance improvement
of many of the aftermarket pipes available for the XR1200, it wasn't until late in the game that I realized that the
performance of the unmodified stock pipes was better than the drilled ones. But
again, here are common approaches to drilling.
Figuratively, the two dimensional
drawing below shows the path that the exhaust gas takes as it moves through the stock exhausts cans. The gas flows down one
perforated tube to the end of the exhaust can, then passes back through packing material to the front of the exhaust can,
and finally exits out the outlet tube to the rear of the bike.
I borrowed the below pic of the baffle inside the stock cans from
JoeP on the XR1200Ownersgroup forum. He split open his exhaust cans for a more major exhaust mod. Having seen
how much even minor changes in baffle length can make on the XR1200's power output, I'm not a big fan of slicing the stock
cans - but then some guys like to make changes for power, some for looks, and some for sound. Regardless, this is a
good image of the actual baffle.
I drilled my baffles in two locations. Some riders only use
one of these approaches, and the size of the holes can be changed as the rider desires.
First, I pulled off the cans and drilled about a 1/2" opening where
the arrows point. This allows some exhaust gas to bypass the full routing of the internal baffle and exit more directly
through the exhaust cans.
While the above picture shows the baffle removed from the exhaust can, I did not disassemble the
exhaust cans to drill the holes in the baffles. The below shows the drilled hole and the main path of the exhaust, in
a still assembled exhaust can. This is what I mounted on the XR.
Rotating the exhaust can 180 degrees, here is a look down the main path of the exhaust baffle.
You can just see the edge of the drilled hole inside the can, at 9 o'clock at the edge of the opening.
Next, I drilled 3/8" holes in the ends of the cans. When
I drilled the holes, I had pulled the cans off and marked the centers of the holes to mirror the exhaust outlet. For
a better cosmetic appearance, it would be better to mark the hole centers while the exhaust was still assembled, so that the
holes line up.
Some people drill these holes larger. The thought is that this bleeds off exhaust
gas half way through its flow inside the exhaust cans.
In reality though, all that drilling seems to do is negatively affect the
harmonics of the exhaust system flow, slow down velocity, and ultimately hurt performance. It was a neat experiment,
but I would not recommend this as a performance enhancer.