Exhaust manifold structure and operation
Cast manifold vs Tubular manifold
Almost all of the factory’s initial installation exhaust manifolds are cast iron, short manifolds that allow cylinder exhaust to be led into a single flow pipe. For the car manufacturer, the functionality of the exhaust manifold is a secondary value after the cost of production and the efficiency of the assembly line.
At its purest, tuning the motor is the same thing as tuning an instrument - the oscillation frequencies are optimized so that the resonances feed each other and the operation becomes self-enhanced. An essential component in tuning the engine to the right key is a damper exhaust system consisting of pipes and connectors (ie collectors), together with the intake manifold and camshafts. Pulsating exhaust gas flow is used for the tuning. When the fuel mixture is ignited in different cylinders during an engine cycle, the phase difference of these ignitions can be converted through mathematical modeling to an exhaust manifold length where the exhaust pulse flowing at the junction of the two branches causes the second cylinder exhaust valve to be optimally flushed. This makes it possible to increase the efficiency of the motor and increase power and torque.
Naturally aspirated vs supercharged
The design criteria for the exhaust manifold are also greatly influenced by engine breathing. The naturally aspirated engine is very critical for exhaust manifold sizing. The pipe size must be kept within the correct tolerances to maintain the kinetic energy of the exhaust gas. Even more important is the correct length of the branches so that the reflection of the counter-pulse in the collector is timely.
The exhaust manifold of a mechanically supercharged engine resembles externally the naturally aspirated equivalent, but is slightly different in size. The exhaust pulse is very sharp due to the high degree of filling caused by overpressure. Therefore, smooth removal of the exhaust gas must be prioritised: a collector structure with the most efficient form must be chosen and the higher temperature of the exhaust gas must be taken into account.
The exhaust manifold of a turbocharged engine is somewhat different from the previous ones, because then the exhaust manifold has a great effect not only on flushing the engine but also on the operation of the supercharger. After all, the energy needed to rotate the turbocharger comes to the turbine blade through the exhaust manifold. However, if the engine is to be able to function at lower speeds as well as in partial gas ranges, functional sizing must also be pursued as far as possible – this is where the so-called pulse exhaust series comes into picture. As with a mechanically supercharged engine, the exhaust pulse is strong and its flow should not be restricted by using an unnecessarily small tube size. At the same time, bear in mind that an oversized tube size slows down the flow and reduces the efficiency of the pulse operation. With many racing turbochargers, one or two additional external waste ports are connected to the exhaust manifold as an additional element. The size of the waste ports as well as the connection to the flow should be carefully planned for each motor in order to maintain the desired boost pressure stably.