Mercedes X will get £100m in extra cash this year, but only if it wins the best-selling class of the new 2017 GT3 series.
The £50m award is for the 2017 Porsche 919 Hybrid, which has the most-popular GT3 class of all, the top six cars in the new GT3 championship.
But the new Porsche 939, which is a GT3 competitor, is not eligible for the award, despite the fact that it is one of the best cars on offer for the class.
The award for the best GT3 car comes from a list of cars from the GT3 Championship that will be voted on by the public.
Mercedes has a 50% share of the vote in the GT2 class and is the top-ranked car in GT3.
But Porsche’s GT3 champion, the 919, is excluded.
The first car to win the award will be the Porsche 929, which will receive £50,000 this year.
The other six cars to be voted will be a Porsche 918, a Porsche 911 GT3 RS, a Lamborghini Huracan LP640 and a Lambo R5.
The winning car will be announced on November 6.
A second round of voting will take place on December 2.