All about Silencers and Exhausts - For those who want to know how their Royal Enfield bikes will be affected if they change their silencers

hi guys since exhausts systems are such a hit on our forum and everybody seems to have their own take on the matter I decided to write abt it
everybody is familiar with the four strokes of an engine (is hope) our beloved bullet is a four stroke engine, during the last stroke of the piston the burnt fumes or gases have to escape the cylinder barrel fast to clear space for the next batch of fresh air fuel mix to enter the cylinder namely the suction stroke, on a conventional type exhaust system (O.E) muffler the exhaust gases do not escape quickly as there is a certain amount of back pressure caused in the cylinder due to the baffles in the muffler and inlet manifold, also one must also realise that exhaust gases are hot and need to disperse, a free flow exhaust normally has no baffles, this in turn allows the gases to flow our without any restrictions and the cylinder is rid of all the exhaust fumes faster as compared to a stock exhaust........now is am sure you are wondering y I have been discouraging everyone using free flow gases and causing damage to your engine, well the answer is fitting a free flow exhaust causes the exhaust gases to go out freely this also has an effect to the intake of the engine, the vacuum at the inlet manifold will also increase thereby demanding more fuel into the cylinder via a carburettor or a fuel pump, one must understand the ration of petrol and air that goes into the cylinder has to be correct if it has an imbalance it can affect your engine, say for e.g. u fit a free flow exhaust with no baffles on ur bike, you will definitely get an good acceleration and u will feel the difference (apart from the noise) but the mix that is going into the cylinder was calculated with the back pressure caused by the O.E exhaust now that u have fitted the free flow the mix is to lean, this will get the exhaust valve to turn hot and I mean real hot this in turn can damage ur valve seat and eventually the valve ,to counter attack this problem u need to increase the air fuel mix going to the engine and u can only do this by re jetting the carb and using a cold air intake filter,i was avoiding a lengthy explanation on this topic but after I guess it was needed .only a qualified mechanic who has some experience working with rally spec vehicles will know this ,most of them won't even agree to my explanation.
this is for our bike now with more than one cylinders in play the ball game is a bit different, a stock exhaust manifold ( also known as a header manifold) is usually made of a consolidated type which means all four cylinders (in case of a four cylinder engine) combine into a single manifold that connects to a bend pipe that will either houses a turbo charger or if not turbo then a catalytic converter then a stock muffler and then a tail pipe
so HEADER-TURBO-CATCON-MUFFLER-TAILPIPE ( the cat con is always present irrespective of the turbo being there or not)
So what does the cat con do? the cat cons job is to reduce pollution by a neutralising the exhaust impurities, but the cat con also increases back pressure of around 1 to3 psi,this is not harmful but only reduces the efficiency of the engine where it could have performed better, then the muffler, the stock muffler is a series of baffles that let the exhaust travel within itself to reduce sound.the cat con by itself is another subject and i am not exaggerating on it here
for a multicylinder engine to perform u need to change the exhaust header, a performance header will be tuned to suit the vehicle it is built for, pipe diameter, bends etc are very crucial to the design, a sport header will have individual pipe outlets for each cylinder, so in a four cylinder vehicle u will have 4 pipes sticking out of the head, as per firing order 1-3-4-2,pipe no 1 and pipe no 3 will go a little distance and join so will pipe no 2 and 4 so u are left with 2 outlets coming from a 4 cylinder engine, this then goes to a free flow muffler also calculated for the specific vehicle or engine it is designed for, both these together complement a free flow exhaust, by just changing the muffler makes no sense, again only noise is achieved ,u can immediately tell if a car has a sport header or a normal header by listening to the exhaust, a sport header exhaust will have a very grumbling sound as u can hear each cylinder firing (music to my ears) and a stock header will only make ONE loud sound

so after reading this I hope u have some idea abt sport exhausts and free flows, there are many more topics related to exhausts,Turbochargers,EGR systems,heatshrink wrapping on exhaust pipe, if anybody wants to know anything more pls message me thanks

i am attaching pics of stock mufflers,free flow mufflers and both types of exhaust headers. 

Posted by my friend Yorik