Apart from being more powerful, the McLaren 675 LT is also supposed to be 220 pounds lighter than the McLaren 650S, but it's not a replacement like the 650S was for the 12C because this track-focused car will be limited to 250 units after it debuts at the Geneva Motor Show.
Take all this with a grain of salt, but Autocar reports that the 675 LT is coming to fill the gap between the P1 and the 650S before the entry-level Sport Series is launched in April at the New York Autoshow. They even got a picture of it:
And yes, that camouflage pattern is indeed a zillion 1997 F1 GTR Long Tails. We know they are good at this.
So the 'P15', McLaren's previously rumored $600,000 supercar turns out to be a modern day LM car with a new front and rear, added side air intakes, 666 horsepower, and more than 500lb ft of torque from its 3.8 twin-turbo V8. At this point, I shall point out that the same engine can do 727 hp in the P1 at 35 psi. Since this car remains road legal, I wouldn't be surprised if McLaren's next idea was to built a 675 LT Sprint for track use only.
More important is the weight savings, which is believed to be 220 pounds, putting the 675 LT's weight at somewhere around 2,711 pounds dry.
As for the 666 horsepower figure in a British car...