were merely routed directly to the intake manifold, the supercharger would blow backwards through the turbocharger compressor rather than pressurize the intake manifold, as that would be the path of least resistance. Thus, a diverter valve must be employed to vent turbocharger air until the appropriate intake manifold pressure has been reached. Disadvantages The main disadvantage of twincharging is the complexity and expense of components. Usually, to provide acceptable response, smoothness of power delivery, and adequate power gain over a single-compressor system, expensive electronic and/or mechanical controls must be used. In a spark-ignition engine, a low compression ratio must also be used if the supercharger produces high boost levels, negating some of the efficiency benefits of a lower-displacement engine. Applications The concept of twincharging was first used by Lancia in 1985 in its Lancia Delta S4 Group B rally car and its street-legal counterpart, the Delta S4 Stradale. The idea was also successfully adapted to production road cars by Nissan with their March Super Turbo. Additionally, multiple companies have produced aftermarket twincharger kits for cars like the Subaru Impreza WRX, Mini Cooper S, Ford Mustang, and Toyota MR2. The Volkswagen 1.4 TSI is a 1400 cc engine – utilised by numerous automobiles of the VW Group – that sees use of both a turbocharger and a supercharger, and is available with eight power ratings: Volvo produces a twincharged 1969 cc inline-four engine that is utilised in their T6, T8, and Polestar models. The T8 adds onto the T6 with a rear electric motor. Jaguar Land Rover produces a twincharged 3.0L inline-six engine. The Danish Zenvo ST1 supercar makes use of both turbocharging and supercharging in its 7.0-litre V8 engine. Alternative systems Anti-lag system Anti-lag systems work in one of two ways: by running a very rich air–fuel ratio and pumping air into the exhaust to ignite unburnt fuel in the exhaust manifold, or by severely retarding ignition timing to cause combustion to continue well after the exhaust valve has opened. Both methods involve combustion in the exhaust manifold to keep the turbocharger spinning, and the heat from this will shorten the life of the turbine greatly. Therefore, in spite of twincharging's complexity, its largest benefit over anti-lag systems in race cars is reliability. Variable geometry turbocharger A variable-geometry turbocharger provides an improved response at varying engine speeds. With an electronically controlled variable angle of incidence, it is possible to have