Look up HIGH POWER N2O.
It works by injecting N2O(nitrous)(laughing gas) into the engine where the high oxygen content of it better supports combustion of the petrol mixture and so increases power.
It also injects more petrol at the same time, this is to give a cooling effect, as n2o burns so bloody hot, can be used on diesels, where it is VASTLY much better than petrol, as the diesel engine is tougher to start with.
Expensive for smaller gains, expensive in use with constant bottle refills, totally street legal though.
tabetha