Serial / Parallel Twin Turbo Set-up

Background: Turbochargers typically are good at creating boost at high RPM, but are inadequate at lower RPM, making a turbocharger engine perform like a normally aspirated engine at low RPM and like an engine with much larger displacement at higher RPM, giving the impression of lacking low end torque. Typically a twin turbo set-up consists of two small turbos in parallel, but still with the same problem. For a fixed torque the amount of air needed to be moved is about proportional to the RPM. Therefore a restriction in the flow path is very tolerable. By connecting the turbochargers in series at low RPM the gas velocity about doubles (half the area) and this makes the turbine (exhaust) side spin faster. Connecting the compressor section in series about doubles the pressure (halves the air flow capacity) and since less air is needed this is fully acceptable.

In

Ex

In

Ex

Front Header

Rear Header

Air Cleaner

Front Turbo

Rear Turbo

Fig.1 shows a flow diagram for a Series / Parallel Twin Turbo Set-up with a triplet air valve assembly for the exhaust and a functionally identical one for the intake air. The valves in this diagram are set for series configuration on both exhaust and intake.

In

Ex

In

Ex

Front Header

Rear Header

Air Cleaner

Front Turbo

Rear Turbo

Fig.2 shows a flow diagram for a Series / Parallel Twin Turbo Set-up with a triplet air valve assembly for the exhaust and a functionally identical one for the intake air. The valves in this diagram are set for parallel configuration on both exhaust and intake.

Although not shown the pictures, the three exhaust valves are on the same axis and the three intake valves are also on the same axis. The engine is shown and labeled as a transverse rear mounted V8 engine as in the Lamborghini Jalpa. This will work with any other IC engine as well.

Since the hot and cold side can be switched independently the system has four states.

A concern could be the smoothness of the serial-parallel transition, but this could be staggered by first making the transition for the intake only, then the exhaust only and finally both intake and exhaust or some other variation.

A further advantage of serial connection at low RPM is exhaust (and intake) silencing minimizing the need for a muffler. The air valves are not expected to have to be fully sealed.