Stage 2 is not a definitive standard so it varies from tuner to tuner and in the case of a tuner like APR they create several versions of what they label as Stage 2 based on the fuel being used 91,93 or 100oct. To see what various tuners claim for stage 2 go to the their websites.
APR,
Unitronic,
GIAC, etc. to get an idea of the range and required hardware associated with their specific claims.