The chemical name is N2O and it differs from the medical laughing gas (for anaesthesia) because it contains sulphur. In contrast to water injection the temperature is lowered in the combustion chamber by up to 70°C, and also one third of oxygen is added, pushing the combustion a lot. Try it yourself: If you hold a just burnt down match in a mug with oxygen, it will start to glow again.
Exactly like oxygen, laughing gas is not ignitable as such. Both substances need in addition hydrocarbons, therefore, oils or grease should be kept away from the levels and their screw connections. Also the sealing of the pipes should be checked. Nitrous oxide is used, actually, only for improving the acceleration and can increase engine torque and engine power if you provide the right dose by more than 50%. The equipment can be installed at a relatively reasonable price. There are even already suppliers who offer a Vehicle Type Approval for certain vehicles. They are easy to handle, taking few specifics into account.
Without Vehicle Type Approval you should use the laughing gas only in barred areas. If you use it on a public street without extra permission, you lose the operating permission for your car, which can cause serious trouble, e.g., in case of an accident, regardless whether you are responsible for it or not. Of course you can try to get a permission for the usage of laughing gas, in Germany a new main certificate with very high costs is required for this.
Of course the complete engine drive has to manage much more strain; it is the same as if you would insert a turbocharger afterwards. Forged pistons might be useful, although the total thermal and mechanical strain is not reduced with it. Thus heavily strained engines feature an additional oil spray cooling which takes a very high expenditure if inserted afterwards. What about the clutch, gearbox and axle drive shafts? How do they manage the additional torque? 20 percent increase may be possible for some vehicles. Nevertheless, it seems only a matter of time which part gives in first. 04/07