Exhaust Tuning in Cars
Posted by
peter
Sport exhaust are a very important modification which most people do however it is a bit misunderstood. Its main job is to break the sound from the engine and to remove the gases efficiently. However this does not mean you fit bigger pipes which look more like drain pipes than exhaust pipes. This will produce a negative effect. Although it is very important to get rid of the exhaust fumes so there is no backpressure built up(the pressure in the engine because the exhaust fumes are not released properly).
However another factor comes into play. This is the speed of the exhaust gases. Bigger pipes will reduce this speed and smaller piper increase it. You have to get the speed balanced with the intake and the capacity of the engine to give an ideal flow rate with the least back pressure.
This will require you to have different bore size for different different RPM of the engine which is impractical so an allround ideal bore size is selected. Aftermarket exhaust are generally good at higher RPM. Some performance cars also have a double bore size. This they manage by having a mechanical clip or valve which changes according to the rpm of the engine to change at lower and higher RPM limits thus giving optimum flow rate at both these speeds.
The general tip is to have a bore size as following. For a 1.6l engine go for a bore size of around 1.5-2 inch. Below 2.5l go with around 2 to 2.25 inch bore size. For engine size above this go with a 3 inch bore size. Although over 2.5l it is better to go with double exhaust with each exhaust equal to half the actual engine size. Example: for a 3.0l engine go with double exhaust with each using exhaust of about half the engine size that is 1.5l engine approx 1.5-2 inch bore. For a 5l engine you can go with dual 2 to 2.5 inch bore.
When gases are required to flow from larger pipes to smaller pipes make a conical joint. With step joint there is turbulence which causes interference in the proper exhaust system.
Aftermarket exhaust are generally better however you can buy a custom stainless steel exhaust system for your car also. Generally a 4-2-1 exhaust is better where the 4 exhaust header merge into 2 pipes and then finally into 1. This helps maintain torque at lower RPM. Performance cars might have a 4-1 exhaust where all the pipes meet into a single exit pipe or a 4-2 exhaust where there are two exhaust pipes. They are suited for higher RPM and can be found in race cars and in many Honda VTEC engines.
Performance exhaust pipes are made of stainless steel as they are lighter and have much smoother inner surface. It is important to have fewer bends.
Having high temperature under the bonnet is a big killer of the performance of the car. It is better to wrap the manifold with heat resistant material. This will help the catalyst in reaching its optimum performance quickly and also increase its life.
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