Stage 1 is as said a remapped chip to run a higher boost pressure along with reprogrammed timing curves, this will see power at around 270HP +

Stage 2 is standard turbo, with green injectors and 3 bar map sensor but running a higer boost pressure again hence the need for a uprated MAP sensor, this stage is usually skipped and people jump straight to stage 3 because of the minimal cost difference between the two, Power for this is 300HP +

Stage 3 is as stage 2 plus a bigger turbo, running again higher boost pressure, for this reason the turbo is uprated to a hybrid T34 which the Escort Cosworth had as the T3 will be on it's limits by now, this is basically sized between the standard T3 and the T4 of the RS500, and a bigger intercooler to cool the boosted air now produced. Power for this is 330-350HP.

The power is the same for all the Sierra range the turbo being the problem after stage 2 hence why it is uprated. With the RS500 and Escos this is not a problem as they have bigger to start with.

Edit: Forgot to mention the uprated actuators as has been said.

Martin