Yamaha 1300 Tourer - Yamaha 1300 Tourer Fansite

OK folks, here’s the scoop on modifying your stock muffler. Just recently, I was able to acquire a complete exhaust system for a 1300. My reason for looking was twofold. First of all, one of the heat shields on my bike was damaged during transport to the dealer. It was barely noticeable, but I’m kind of fussy that way, and wanted to replace it without having to pay dealer prices for a new one. Secondly, I wanted just a little more noise without coming up with the big bucks for an aftermarket unit, and thought it would be fairly easy to modify the stock unit. I have a machine shop, and the exhaust system which I found on a local classified internet site was reasonably priced, so what the hell, lets take a look at the insides. First of all, I’ve gotta tell ya, this is a very well constructed unit. It’s built like a tank, the welds are all outstanding, and the guts are made of 300 series stainless steel. It will last a lifetime. In the front portion of the muffler is a catalytic converter which is large enough not to cause much restriction of exhaust gas flow. Beginning at the catalytic converter is a large double walled chamber, the outer being the tapered chromed tube that forms the outside of the muffler, and an inner tube, made of perforated stainless steel (also tapered) that runs the full length of the large diameter of the muffler. In between these two tubes (wrapped tightly around the perforated tube) are several layers of very dense, heavy duty fiberglass insulation / sound deadening material, about 1/4" thick. Just behind the catalytic converter is a chamber about 4-1/2” diameter by 5” deep. This is an open chamber with no baffles or restriction of any kind. At the end of this chamber is the first and only bulkhead. It is welded to the inner perforated tube, and is the beginning of the actual exhaust opening you see out the rear end of the muffler. This 1-5/8” I.D. tube is a two piece assembly, made that way so that the plug you see from the rear end, about 12” inside the outlet can be easily installed during manufacture. For all practical purposes, the outlet tube is one piece, because it has been welded together, and there is no way to separate it without completely disassembling the entire muffler to get to it. Now this inner tube has small perforations punched in front of and behind the plug. There are twice as many holes (122) in front of the plug, (on the catalytic converter side) than on the exhaust (rear) side(66). The holes are all about .140" in diameter. So what happens inside your muffler is this: gas exits the catalytic converter into the first large chamber, hits the first (and only) bulkhead, is forced into the front part of the exhaust pipe, hits the plug, is forced through 122 .140” dia. holes, out into the large chamber between the exhaust pipe and the inner wall of the muffler, and having nowhere else to go, it is finally forced through the 66 small holes behind the plug and out the tailpipe. Whew! What this all boils down to is this. If you want direct flow from the catalytic converter out the tailpipe, all you have to do is go in with an 1-1/2” hole saw, drill out the plug, and that’s what you’ll get. I have no idea what it will sound like, and my “test muffler” is in so many pieces it will never be put back to stock condition with just the plug removed. Doing this will relieve some back pressure (is that good?) by increasing the area the exhaust gas has to escape through from 1.01 square inches to 1.77. Personally, I would not do this modification if I had to do it to the only muffler I had, the one on my bike. Stock mufflers are very expensive. For most of us, it probably makes more sense to buy a take-off muffler to modify if you like to experiment, or just buy an aftermarket unit and keep the stocker for replacement at a later date. Some states legislatures are now starting to discuss legislation requiring that motorcycles have only stock exhaust systems, and those that don’t will not pass safety inspection, and of course, those will not be permitted registration renewal. I will continue to experiment with my test muffler though, and if I discover anything that may be of interest, I will pass it on.