Can Aquila offered with seat backrest? And can the silencer of this bike be replaced with sports bike type silencer?
No it doesn’t offered with seat back rest but this is not a big issue you can replace or modify the seat with the help of local fabricator, but replacing bikes silencer is indeed a big issue. Many bikers uses modification in their exhaust to get so called exhaust tune and sporty look but one should consider the effects of this modifications.
The efficiency of engine is directly affected by speed of the engine, exhaust valve opening, exhaust port dimensions, exhaust pipe location and position, dimensions of catalytic converter, muffler design. All these parameters finally affect the back pressure of exhaust. Back pressure in the exhaust is required to remove the gases from exhaust pipe.
After completion of exhaust stroke, Pressure in the exhaust pipe becomes more than the atmospheric pressure. Because of this, gases flow automatically from pipe to the atmosphere with high velocity and produces tune that we listen from exhaust.
Now to get the smooth (Nearly Laminar) flow of exhaust gases, designer keep the value of back pressure within limit by introducing slant in muffler (You can observe this slant in each bike above 125 cc), muffler design, path travel by gases etc. according to the capacity of engine. Now at the time of modification, we are influencing following parameters:
First of all we are increasing the total length of exhaust because of which the path travel by the gases increases. Now as the gases have to move long way, velocity developed in the pipe decreases by the time. As per the rule, velocity and pressure are inversely proportional. So finally pressure will increase and flow gets chocked.
As we are increasing the exhaust pipe length, we are introducing more bends in the exhaust pipe. Each bend causes flow restriction and friction losses in the gas flow. This leads to chocking of flow again.As this two major factors result in chocking of flow, the next batch of burned gases coming out from cylinder don’t find any way to move.Finally the efficiency of engine reduces drastically and burned gases remain in the cylinder. These burned gases got mix with the fresh charge and burnt again and again. This process leads to generation of more emission.
Changed exhaust manifold angles would result as higher fuel consumption, low brake thermal efficiency, and high exhaust emission.
I personally suggest you not to modify your exhaust ever. Because it is optimum design provided by the manufacturer and designed by their best designers, most important by doing so you will void warranty. Even then if you are so passionate about noisy bikes (there is vast difference in tune and noise), first you get the calculated back pressure and then get the correct dealer for correct exhaust.