h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Nitrous oxide also has an additional useage in anti-lag systems for engines utilising large turbochargers that produce high levels of boost but only begin prudicing boost high in the rev range of the engine.

As more fuel is burned by the engine through the use of nitrous oxide there is an increase in the volume of exhaust gases produced during each cycle of the engine. This increased volume of exhaust gas will cause a turbocharged car to spool earlier in the rev range than standard due to the increased exhaust flow through the system (as turbochargers are powered only by the exhaust flow through the turbo manifold).

This increase of gas flow can cause issues with some turbocharger setups. The maximum boost of a turbocharger system is controlled by a "wastegate", a bypass valve that allows exhaust gasses to pass around the turbo system, limiting the maximum spin rate of the turbo (and thus it's maximum boost pressure). However, if a nitrous system causes too much of an increase in exhaust gas volume, the wastegate may not have a high enough flow rate to prevent more exhaust gas than normal passing through the turbo and causing it to spool to higher than expected levels. This could cause damage to the engine if this has not been taken into account during the setup of the turbocharger and nitrous systems.