The Ford Focus RS has been tuned to 368bhp and 339lb ft of torque by Graham Goode Racing.
That's 68bhp and 14lb ft more than the standard car, at a cost of £3750 plus VAT for the kit, its fitting and a 12-month, 30,000-mile breakdown warranty.
Graham Goode Racing says it has refined the car to produce "a driveable, reliable, yet stunningly rapid fast road upgrade package".
There are no internal changes to the engine; the modifications comprise a carbonfibre cold air induction system, a large-capacity air-to-air intercooler, large-volume fuel injectors, silicone boost hoses, a large-bore exhaust turbo front pipe and sports catalyst, and an ECU remap.
GGR's technical manager Alastair Mayne said the company deliberately restricted the torque gains to ensure the car remained workable.
"Even with the Revoknuckle front suspension and Quaife differential, gaining sufficient traction can be a problem," he said. "Bearing that in mind, we made a conscious decision to limit the engine's torque, although there is certainly more to come from the motor if we wanted it."