I mean even changing the exhaust makes a difference in performance.Everyone is saying that Try slip on exhausts and such.For me it‘s left me baffled?Everything of use happens in the power stroke,right?So then why is the exhaust that much of a difference?Aside cutting out the noise what other use is there for it. Let‘s say noise isn‘t a problem.Would cutting out hollow metal tube and replacing the exhaust be of any difference to the motorcycle?Would the engine be damaged by it?I Mean the exhaust is technically a free flow right?
No the exhaust is not a totally free flow. Some back pressure is there. Now in motorcycles way more than cars the exhaust is designed (tuned) to the air/gas input. The entire flow of air and fuel in a motorcycle engine is designed for efficient flow and performance. If you change the input (jets) then consider changing the exhaust. If you just change the exhaust it will change where torque and power come in the RPM. While some exhaust systems do help in the power band many cause a fall off of power at higher RPM levels actually causing the bike to not reach it's original top speed. Some cause a difference in power output through the mid-range causing longer times for getting up to higher speeds. While these after market exhaust systems may sound better than stock they are not designed as well as most stock exhausts are to take advantage of the actual input to the engine. Most Japanese sport bikes have a very well designed flow system, playing with it could cost you some power somewhere in the power band. Therefore if you want to change the input (jetting in the carbs) then consider changing the exhaust to match the increase in fuel and higher burn temps and same for if changing the exhaust you need to look at air and fuel input to match exhaust flow capacity, this is far more critical in a high performance motorcycle engine than in a car due to RPM levels and speed of reaction.
Think of a motorcycle exhaust system as a finely tuned pipe organ. The manufacturers spend tons of money getting things just right so the engine runs at the maximum power level possible and has the broadest power band possible. There is so much more to an exhaust system then just a pipe moving the exhaust gasses away from the motor. There is a pulse that travels back up the pipe and the timing of this pulse is critical in the way the exhaust gasses are moved out of the combustion chamber. The gasses from one cylinder can actually help scavenge the exhaust gasses another if the timing and pipe lengths are correct. The mufflers and pipes all work together to put the power band in a useful RPM range that you can actually use. It might be possible to get your motorcycle to produce more horsepower with a different exhaust system but the power band might only be useable over a two hundred rpm range and everywhere else it might actually produce less power. Slip-ons are great money maker for those who produce them, and in some cases the might actually make a few extra horse power, but usually you are better off with the stock exhaust. The manufacturers spent a lot of time and money getting your system to all work together. Intake, exhaust, engine, computer, electronics and injectionthey are all tied together in today's bikes.
Last question about free flow zone , NO! It is called SCAVENGING, a certain amount of back pressure actually helps pull exhaust from the cylinder and draw fresh fuel/air into the cylinder. I was on a group run several years ago and some kid showed up with a 600 sport bike and a 4 straight pipe, every small incline made him get on the gas, he had no torque to pull with and was annoying as hell to listen to. These were 50 bikers, at least a few of them would have been into the loud is safe theme, this kid had no friends and was relegated to the the end of the line, he was still heard at the front.
