Performance Modifications: Exhaust Systems

As we all know the job of an exhaust system in a car is to route the spent gases from the engine out into the atmosphere. However, cars today use exhaust gases to drive turbochargers. To improve performance of a car the exhaust flow can be optimised. All this creates direct impact of exhaust gases on the engine’s performance. 

To modify an exhaust system the easiest thing to do is replace the stock muffler with a high performance free flow muffler. However the inlet and outlet of the muffler should be the same size in terms of diameter as the front pipe and tail pipe. 

The primary pipe diameter and the length of the exhaust manifold are the most important factors in a exhaust design. The engine size, number of cylinders and usable RPM determine the size of the pipe diameters and length. 

In anything from a 1600cc four cylinder engine to a 2400cc six cylinder engine with a maximum RPM of 5500 should have a primary exhaust diameter of one and a half inch and a primary pipe length of 34 – 37 inches. On a four cylinder engine all four primary exhaust pipes should join in a single collector. On a six cylinder engine the exhaust pipes from cylinders 1, 2 and 3 should join a single cylinder while pipes 4, 5 and 6 should join in a second collector. A Y-pipe could be used to connect exhaust flow from the two pipes into the tail pipe. 

When the pistons go into their downward stroke they create vacuum in the cylinder, this results in reversion of exhaust gases back into the combustion chamber. This contaminates the fuel air mixture and decrease the efficiency of the engine. Anti-reversion headers that have a built-in lip which restricts exhaust flow back into the combustion chamber can be installed to ensure clean air flows into the cylinders. 

In a turbocharged engine there may not be enough space for equal length exhaust pipes that connect at the collector therefore a log type header in which the pipes have to meet at the collector before the exhaust pipe spins the turbine of the turbo charger. The size of the collector will depend on the size of the turbine the exhaust gases have to spin. Also, while the system is being designed it should be kept taken into consideration that the headers have to be able to take the weight of the turbocharger. The wastegate should be located either after the collector or after the last exhaust port on a log type manifold so that it does not interfere with the pressurised flow of exhaust gases spinning the turbine. The wastegate has to detect the pressure of gases spinning the turbine without hampering the exhaust pressure. Lastly the tail pipes have to deal with much higher temperature exhaust gases in a modified engine with a turbo charger and exhaust manifold and therefore needs to be replaced with a thicker pipe with additional bracing and swaged joints for heat expansion.