You can tell it apart by the new paint, and literally nothing else.
What it is exactly that constitutes a production version in the world of race cars is already a bit hazy, but McLaren decided to confuse the matter a bit more when the P1 GTR track car debuted at Pebble Beach as a “design concept,” with a “production” model promised for Geneva. Well, the Geneva-bound version of the car has just been announced and it turns out that it's basically the same, with McLaren itself saying the car has had "only minor modifications."
But that's all fair enough, we could even see the fact that so few modifications were needed as a sign that McLaren really did pour every once of its effort into making the P1 the best it could be right from the start. The difference in downforce between the road car and the GTR is now officially 10 percent, and in racing trim, the car weighs a total of 50 kg (110 lbs) less than the road car. Combined power output of the 3.8-liter twin-turbo V8 and uprated electric motor has been increased to 986 hp with a number of drivetrain components having been changed to race-spec parts, and the emissions control equipment removed for weight saving.
The most noticeable difference between this and the concept version of the car is the new livery, which McLaren is especially proud of. It pays homage to the 1995-96 Harrod's Mach One F1 GTR, chassis #06R, which took third place at Le Mans in 1995 and sixth in 1996. A different McLaren F1 GTR actually won Le Mans outright in 1995, but apparently McLaren thought this was the better livery. The car will be used for the McLaren P1 GTR Driver Programme, starting at Circuit de Catalunya in Spain. But the car itself will be shown in just a couple of weeks. We'll bring you photos from Geneva.