1. By changing the flat-top pistons to high compression ones that curve upward to result in a higher compression ratio. However, since the air and fuel are both more highly compressed, there will be more heat. The fuel will start burning spontaneously (before the spark plug ignites) and this causes knocking (which is a flame front coming down at the piston trying to go upwards), and this reduces engine power. It is for this reason that only higher octanes are usable in modern engines, because lower octanes like 92 are more prone to knocking.
2. Turbocharging. This gives maximum power when the turbocharger is spooled up beyond 3000 rpm, but below that engine speed the turbo will slow the engine down as it is exhaust driven. This is called turbo lag. Furthermore, to be prepared for the very high effective net engine compression that results when the turbo comes on fully, the engine must have an inherently low compression ratio such as 8:1, which further takes away power before the turbo is up. This in all causes higher fuel consumption in turbocharged cars.
3. Supercharging. This gives an increased charge proportional to rpm, but loads the engine straightaway like an aircon pulley. At low rpm the boost effect is also noticeably absent.
This is done using a Surbo (air-suction-turbo, an engine back pressure activated vortex generator). The Surbo gives higher air pre-compression in the air intake, outside of the cylinder so it does not increase the fuel compression in the cylinder (like in 1.), and does not cause knocking. In fact, the owner of a '09 Chevrolet Captiva 2.4 reported that knocking noises were gone after the Surbo was fitted. The Surbo achieves the desired higher compression safely without causing excessive compression heat in the engine. By the time the Surbo-assisted engine hits the rpm red line, the accelerator is pressed just halfway, so the Surbo gives good engine power with safe, moderate compression. You can still remove the rev limiter though, and extend the rpm by flooring the accelerator, using all available compression. The Surbo is also the least costly and most fuel-efficient way to improve compression.
The Surbo can also be used in
1. Very high compression engines to lessen the fuel input and prevent knocking, or enable usage of lower octane fuel (this is because with a Surbo, less of the accelerator is pressed, so fuel put in is less).
2. Turbocharged engines, to cut the turbo lag. The Surbo's pre-compression from low rpm before the turbo is up increases the engine's inherent compression, and the increased air flow moves faster through the exhaust, thus spooling the turbo sooner (at a lower rpm) so cutting the lag and fuel consumption, and improves overall response. Surbo-fitted turbo vehicles include the Volvo S60 T6 (250 bhp) and XC90, Subaru Forestor, Daihatsu Charade Turbo 1.0 and GTti, Toyota Starlet 1.3 Turbo, and turbodiesels like the VW Caddy TDi, Opel Combo and Mercedes Vito 110 and automatic 112, amongst others. The Surbo might be added to modern high-compression petrol turbocharged engines with lower capacities, for while these have sufficient power most of the time as the car bodies are lightweight, when they are overloaded with many passengers the power may not be enough.
3. Supercharged engines (as in Mercedes Kompressor C180) to increase the low rpm power and enable them to cross more easily into the upper rpm range where the supercharger will take over, especially if it is automatic and normally limited by the gearbox to operate in the lower rpm range.
4. Diesel engines. When a Surbo is fitted in a diesel engine, the diesel engine becomes more powerful even from idle, showing improved engine compression (as diesel engines are compression-ignition). The revs go higher, and visible black smoke is practically eliminated, indicating that less diesel is required to move an engine that has better fuel efficiency due to better compression from the Surbo.