Sneek Peek: K-PAX Flying Lizard McLaren 650S GT3
Earlier this year we were able to get a close look at the K-PAX Flying Lizard McLaren 650S GT3 that races in the Pirelli World Challange series in GT class.
If you are not familiar with the GT class, the allowed body styles within this class are coupe, sedan and convertible. The cars permitted in GT are typically sold in the market as “sports” cars, “sport touring” cars, or performance versions of “luxury” cars. The GT class allows FIA GT3 homologated cars like this McLaren. Forced induction is permitted on cars that come equipped with forced induction stock, or on cars that SCCA Pro Racing has determined need help reaching the target horsepower range. Power output for the GT class ranges from 425 – 525 hp. The allowed weight varies depending on power output and tire size. All of the vehicles in GT are either rear or all-wheel drive.
The K-PAX Flying Lizard McLaren 650S starts off as a standard 650S GT3 race car from the factory but has been modified by K-PAX for the class somewhat. We will try to show what we were able to see. Unlike some other teams were were not allowed to shoot all of the cars goodies so we will have to guess at some of the car's features.
The M838T engine is a 3.8 liter 90 degree, flat plane, 4 valve DOHC, V8 twin turbo that is regulated by the homologation rules to 500 hp and 370 lb/ft of torque with a redline of 8500 rpm. This is quite a bit lower than the 641 hp and 502 lb/ft that the street going engine puts out. The flat plane crank contributes to rapid turbo spool by treating the engine as two 4 cylinders making it easier to design the exhaust manifolds to get pulse convergence. This helps drive the turbines more effectively allowing the engine to develop 80% of its rated torque by a super low 2000 rpm. The valvetrain features roller finger followers allowing aggressive valve motion and low friction. The racing version of the engine has modifications to improve cooling, lubrication and durability over the street version for low operating cost. The engine is dry sump scavenged and features a divided partition crankcase to keep pumping losses to a minimum. As an interesting note the rights for the engine were purchased by McLaren from Walkenshaw Racing who had originally designed the engine for IRL competition. Ricardo then refined the engine into its final production version. 
An Xtrac P1529 transaxle has six forward speeds and is designed for endurance racing applications. This allows for lower maintenance costs. The P1529 is unique as the gearcluster is behind the differential allowing the unit to be extra compact. The Xtrac uses an integrated valve actuator system in the sequential shift drum mechanism to facilitate semi automatic pneumatic shifting. 
The short ceramic coated exhaust system exits above the rear diffuser and probably helps activate it for some additional downforce. The exhaust system has a crossover merge pipe which probably helps low and mid range power. The exhaust design doesn't look particularly efficient but since the car had to actually lose a lot of power for the class it likely does not matter much. 
The engine's heat exchangers for the coolant and air conditioning system are located in the nose of the car. The heat exchangers are fed cooling air by carbon ductwork and exit out the hood through semi ducted louvers. We think the aluminum cover over the coolant heat exchanger is to prevent damage during maintenance. The engine oil, and transaxle heat exchangers are mounted in the car's sides and are fed by ducts that start in the doors and lead to the rear of the car.
