Here's a tune I made for the car. You can try it out if you like and see if it improves things for you, but you also have to keep in mind that the McLaren F1 '94 car has about 865hp and only weighs 970kg. That's a recipe for spinning tires if you don't control the throttle. You will find this on many of the race cars that are very light like this, but which also produce a lot of horsepower, and in order to race them effectively one has to really develop a sensitive touch when it comes to throttle. Using traction control is also an idea. You can't drive these cars with an all or nothing approach to the gas pedal. But like I said, try this tune and hopefully you'll find it useful.