How is a "stage" defined?

[EPa]

How are stages numbered? (I mean why should a stage be numbered 3 and not 2?) Is there a widely accepted standard?
What exactly are the prequisites/guidelines/standards for an engine upgrade to be considered a "stage" ?
What is the difference between stages? (apart from power )

Well, all of the above is actually one question

[93Linear]

No way to give a singular, definitive answer on that ... really depends on the company. Generically speaking, the higher the stage number, the more power will be produced & the more modification will be required. Typical "Stage 1" upgrades are software only ... further stages may include anything from different intake/exhaust to new turbo/new pistons/new injectors ... again all depends on the company and how/what they want to offer

[Chris 9-5]

Upgrades are often shown in “Stages” this gives an easily understood power progression format.

Stage One kits are usually software only and comprise of unique ECU performance software maps to utilise the big margins that saab build into your car at the factory.

Stage Two kits usually enhance the first stage by improving the exit of exhaust gasses by adding a larger exhaust (often cat back only).

Stage Three kits further enhance this progression with a larger down pipe and race catalytic converter.


However different tuners will define their own stages, a Stage 2 from one company may not be a direct comparison to a Stage 2 from another, either interms of parts or performance.