sounds to me like its either a 'redtop' engine turbo conversion (same as that found in the cav gsi turbo 4x4 or the calibra turbo 4x4, courtney can do some powerfull engines based on this unit 300 - 350bhp +,
or it could be the newer astra/vectra engines, which are a turbo as standard, but agian if its been to courtney, it will be a fast motor.
also if he is a good driver in way of not redlining it in every gear and timing his gear change, that would also improve the build up of speed.
still though Seat vs Chav.........