It appears I should have expanded my comment a little.I never meant to suggest that a silencer offers a performance improvement,only that different lengths affect it in different ways.A shorty skews the power more to the bottom,a longer one more to the top.As we all ride with a silencer,the length you need depending on what you are after is the pertinent question,not the fact that it would be faster if you took it off altogether.A shorty is noisier as well due to the fact it has a shorter core and less packing,assuming all else to be equal.
On a noise note,a few years a go a friend got his can am 400 finished and came over for a ride.Now,say what you want about 4t's being louder than 2t's and while this is true in most cases,I've never heard such an ear splitting,brain rattling sound as what came out of this.He had it fitted with the can am accessory performance silencer-a "Disco-Jet"(it was stamped right on it)likely a cool name in those days.Anyway,he replaced it with the stock one after one ride.Whether it was because of the noise or he got tired of questions about his riding style mimicking John Travolta,when he was getting all white gear,his mid hesitation being due to a case of night fever,or having to listen to butchered versions of "you're the one that I want" complete with actions whenever stopped, I never found out.
I do remember thinking at the time that a track full of likely sounding machinery would have been as brutal if not more than the fourstrokes of today.Maybe people were a bit less sensitive in those days.
