[gregsfc]

Like it has been stated, messing around with the exhaust and or just the muffler on bikes is going to vary alot with each design with how it affects performance; the necessity for re tuning; and how it affects mpg. My 2014 Honda CTX700, with a 670 cc parallel twin, ports out of the engine and is almost immediately squeezed into one 1.5" pipe right out of the CAT, so, in my case, most mods will do little, since the exhaust is already compressed coming out of the engine and then some more at the CAT. I've fiddled around with going muffler delete only (not messed with any of the header pipe or CAT), and these are my results are shared below:

I'm not one who can give much technical expertise, but I recently played around with removing my muffler from a 2014 Honda CTX700, parallel twin that weighs nearly 500 lbs wet and produces roughly 46 hp and 43 peak foot lbs of torque on the average dyno test. This is a different kind of bike motor; it's much lower revving than most bikes, because it is basically 1/2 of a Honda Fit car engine, and so, unlike most motorcycles, it has very flat torque but doesn't build up so much as it revs; sort of like a diesel some reviewers say, but owning a diesel car, I'd say; not quite.

Reportedly, the torque curve reaches near peak levels around 3,000 RPM and stays there up to about 5,500, and then, the rev limit is just past that point at only around 6,500. What all this means is that, since this is not really a high-performing bike wherein its strength is flat torque and great gas mileage, any small amount of change in the torque and mpg would be very noticeable, especially if one is recording mpg and paying attention to throttle response, which I've done. I'm anal about recording my mpg, and I ride a regular commute at or about the same speed every day and my data is usually very consistent at any given average air temp.

I first removed the muffler to paint it black. Tried the bike out w/o the muffler and was surprised at how good it sounded (though just a little loud, but not as loud as I expected; but a much deeper, big bike sound than what I expected). I decided to ride around w/o the muffler for a full tank of gas. I think that it lost just a little mpg, because my loss on that particular tank was just a little out of my normal range for summer time, commute riding. As for performance, that's a little harder to nail down, because the extra noise may have been messing with my perception, but it seemed like a slight amount of torque was gone in my normal riding RPM ranges, especially on the low end after up shifting, but it may have been that it just seemed like I was having to give it more throttle to get a response due to the noise being created when I'd throttle back.

I really liked not having that big, heavy muffler though, because now I could hear the engine revs and could upshift more smoothly; and additionally, I could much easier clean under the bike after riding in the rain or wet roads, and my research was telling me that no harm would come to the engine from what I was doing, but someone did suggest extending the pipe past the header out end, closer to the original length, because that would communicate back to the engine closer to the stock level for performance reasons w/o having to re tune. So that's what I tried next. I simply went to a muffler shop, and the mechanic swelled one end of a 1 1/2" o.d. pipe where I could clamp it on about 14" long. That cost me $10. I then went out and got a $5, one.point.five muffler clamp, because my stock clamp was too large; painted everything matte black like my bike trim and clamped it on. Now everything was perfect, well except maybe the appearance, but even that ain't too bad. It's quieter at idle, no more popping while engine breaking, but I still have that deep rumble without being offensive. I also seem to have my torque and mpg back, averaging around 79 on my commute tanks and over 80 on trips, which is what I've had since it got hot out and I switched to a low-profile helmet.