It doesn't pay to tamper with the exhaust system
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When I was a teenager, I was like other kids who were crazy about fast machines.
I rode the Honda S90, CB 100, CI 90 as well as the Yamaha YL2. I met up with friends and we would talk about motorcycles all day long, and once we reached the stage of wanting to modify our bikes, the first thing we attempted to do was modify the exhaust pipes of the bikes we would ride to school every morning.
With our limited knowledge, my friends and I would consider the following: if a two-stroke engine, the exhaust pipe had to be fat like a pregnant woman in the centre and the tail pipe had to be narrow. For four-stroke engines, the pipe must start with being narrow and then expand to being wide like a horn towards the end.
But no matter which choice we made, the results were similar – the noise would be so loud that people’s ears would hurt and the general public hated us.
Once I grew up and started to race cars instead of motorcycles (I drove a Subaru FF and Datsun Sunny with the A12 engine), I started to learn about exhaust-modifying again. This time, however, I learned the difference between the exhaust pipe and the header, which quickly was gaining popularity among car enthusiasts and there were a large number of shops everywhere.
The guys who were the same age as me on the motorsports scene believed that headers would help increase engine output by at least 10 per cent as well as lower engine temperature. But in those days there was much misunderstanding about headers and exhaust pipes.
I suddenly thought about this because a reader named “Mr Racing” has asked me the difference between the header and the normal exhaust pipe, and the pros and cons. After I finished reading the question, my brain suddenly ran back to the time when I was 20 years old.
First of all, the exhaust pipe and the header are two totally different components that work together. We start from the exhaust manifold where the combusted air and fuel mixture exits the engine through the header. There is one pipe for each cylinder and they would all join at a later stage. In some engines, the pipes would join in a 4-2-1 format while in some engines it would be 4-1 (which is the regular format from the manufacturer) depending on the design.
According to the theory, the engine would produce the maximum power and have complete combustion only when the exhaust gas from the engine exits in the shortest time possible. The gases must also exit at the same speed or close to the same speed.
This leads to another theory that the header from the four cylinders must have the same length so that the gases take equal amount of time to exit the combustion chamber.
However in reality, even if the header pipes have the same length, the design and the curves of the pipes result in different exit times of the gases. Hence header shops came up with various formulas in order to ensure that the gas exits at the same speed.
At the same time, the exhaust pipe continues from the header and by law has to extend to the rear end of the vehicle. The law also states that there must be a three-way catalytic converter, which slows down the speed of the exhaust gas further. Many car owners even remove the catalytic converter or increase the diameter of the exhaust pipe, resulting in much higher noise levels than the law allows.
In order to answer Mr Racing’s question, I must say that the exhaust system provided by the vehicle manufacturer is the best choice. Even if you change the header, there are many risks, including slower gas-exhaust speed resulting in poor acceleration, increased fuel consumption and higher engine-heat level than normal. And the louder noise will also make the traffic police stop you more often than others.
If you don’t plan to modify the car for racing purposes, using the standard header and exhaust pipe will ensure that the engine will have a long lifespan like it should.
