A major difference in the design of the exhaust manifold for a turbo exhaust system is the integration of the turbocharger's wastegate. As we've mentioned in our section on turbocharger boost control, the wastegate is used to control boost pressure created by the turbocharger, and to prevent it from creating too much boost pressure. For this reason, the wastegate should be integrated into the exhaust manifold in such a way that it is exposed to as much of the pressure in the exhaust manifold as possible. This means that the wastegate should be located either after the collector where all the primary pipes join together, or after the last exhaust port on a log-type manifold. The wastegate should also be located at an angle that neither restricts nor interferes with exhaust gas flow as efficient exhaust gas flow is required to reduce turbo lag. In other words, the exhaust gas must be able to flow to the wastegate so that the wastegate can experience the correct exhaust pressure in the system without interrupting the exhaust gas flow
THE TAILPIPE
An exhaust manifold for a turbo engine.
There are also a few important aspects of a turbo engine that you must take into account with regards to your tail pipe. Firstly, the turbo increases the amount of air/fuel mixture that is fed into the combustion chamber and consequently increases the amount of exhaust gas that must be expelled from the engine. Secondly, the exhaust gasses of the turbo engine are much higher than a naturally aspirated engine; therefore the exhaust on a turbo engine will be more prone to heat expansion. The flange that is attached to the turbine outlet can experience temperatures of up to 1500°F! For this reason the flange should be beefed up and a minimum flange thickness off a ½ inch with additional bracing is recommended. The rest of the exhaust system needs to make allowance for heat expansion and should incorporate swaged joints.