This makes sense to me. I live about 1km away from the most active airbase in Canada- you do get used to it. I think the campaign is little more then a "kiss and make better" program to appease people that complain. Peel police have always been dinks about sportbikes and exhausts.
Super noisy mufflers.. Really you're not going to see a lot of performance gain from simply swapping to a fart can muffler. Now going to a full cat-back system you probably will, or header-back system- that's where you will see some gains. Usually because the exhausts are larger, allowing more flow and a lot of the restrictions are smoothed out. But there is a point where if it is too large all you're doing is making noise unless you build up the engine so it draws in more air (forced induction, more displacement) and fuel.
The big question really is, at what point do you need to upgrade the exhaust system on a micra? If you're just doing it for the sound.. Well, expect the extra attention. And perhaps the extra attention from the fuzz. Most aftermarket exhausts do offer silencer slip ins for a reason.
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View my fuel log 2015 Micra S automatic: 7.9 L/100 km ... 35.7 mpg (Imp) ... 12.6 km/L ... 29.7 mpg (US) ...