Like some sports reporters, talks too fast with run on sentences, I wouldn't copy his answers in an exam
That is a good video. Valve overlap means if you don't have scavenging some of the exhaust will be pushed into the inlet area when the inlet valve(s) opens, thereby diluting and contaminating the incoming air/fuel mixture. The big takeaway for me from that video is don't play with your exhaust collector(s). The men in white coats have designed your bike's exhaust to work across all rev ranges and conditions...leave it alone. The big cylinder shaped thing at the end of the exhaust was forced onto your bike by the EPA and emissions people. When drag racing (WOT), your muffler is as useful as a wooden frying pan.
There's this one too. It gets straight to the point without all the engineering very few people actually care about (including me lol)
I agree to a certain extent to the previous comments, but you must understand a 4 stroke engine operates completely different from a 2 stroke engine. The back pressure from a properly designed 2 stroke engine exhaust system is one of the major factors for these 2 stroke engines final horsepower & ride ability features. Because a 4 stroke engine develops its power from the compression cycle of its 4 strokes, the exhaust system is best designed to get rid of the ex-spent gases as soon as possible allowing the intake stroke to be free of any back pressure. Take a quick look at the most powerful 4 stroke normally aspirated engines on such likes as drag racers they only have short, non boxed open ended pipes. The same applies to most 4 stroke unsupercharged Aircraft engines, the only reason to design these restrictive exhaust's is to comply with modern pollution regulations. Hey if all you want is a nice reliable fuel efficient commuter fine, but if you want performance from a 4 stroke, get rid of the restricting exhaust & go back to a non computer controlled fuel induction & ignition system. If you look at ultra high revving 4 stoke engines as found in Formula one cars etc, yes you will find 4 into one, 6 into one, 8 into one exhaust systems, but if you look into the science of these, it uses ex spent exhaust gases from previous cylinders exhausts strokes to ad a negative pressure wave to help to create a vacuum for the incoming fuel charge of the nest cylinders intake cycle. Hey its all fun & games & as they say the proof of the pudding is in the eating.
