Prodrive P2

Prodrive is quite well known for its rally car tuning, and it has even had its hand in the F1 business in the past. But it has never really broken the standard road car market, unless you count the rally tuned Impreza P1 that Subaru made available a few years back. But then, the Prodive chaps decided it would be nice if they could have a go at making a road car. So it did. It's called the P2, and it made Jeremy feel really sick.

The P2 was styled by the bloke that did the MG SV, a car most famous for smacking Jeremy round the head. It's powered by some of the most sophisticated technology ever put in a road car. The engine is from an Impreza, but Prodrive has stuck a bigger turbo on it. This means you get a lot of power, 345bhp in fact. And what's more, this car weighs as much as Pete Doherty's brain, so it isn't exactly heavy. It'll do 0-60 in 3.8 seconds and has a top speed of 174mph.

The P2 has two very important systems built into it that make it so fast. The first is called anti-lag, the second is a complicated active-diff which is very hard to explain. So we got engineering expert James May to explain them in detail here for you:

"Right, now bear with me on this one, I think I've got it. First of all, the anti-lag. A normal turbo works by using the exhaust fumes exiting the engine to spin a little sort of propeller thing that drives another little propeller thing in the engine air intake which then spins round very fast and forces more oxygen into the engine. But, at low revs there aren't enough exhaust fumes to drive the little propellers and give the engine its oxygen boost. So, you press the accelerator and have to wait a second or more until there are enough fumes to get the turbo propellers spinning, at which point you go from no power to lots of power. This moment of delay is called 'turbo lag', although another phrase for it is 'bloody inconvenient', especially if you're trying to overtake another car. So, the Prodrive anti-lag system works by keeping the little propellers spinning and forcing lots of lovely oxygen into the engine even when there aren't enough exhaust fumes to turn them normally. And it does this by dumping petrol into the exhaust, just before the little propeller. As soon as the petrol touches the very hot exhaust pipe it explodes and this explosion keeps the propeller turning so when you step on the accelerator there's no irritating wait for it to for it to get spinning and instead you have an instant dollop of big fat power. Or something like that.

Ah, now the active diffs. Yes, there's one of these in the middle of the car and another one on the back axle. The middle one controls what proportion of the torques from the engine go to the back wheels and what proportion go to the fronts. And the diff at the back does the same, splitting the torques between the rear wheels. They're both controlled by a very clever computer that has a speed sensor, a steering angle sensor and something called a 'yaw sensor' which sort of measures the line that the car is taking through a corner. This is very important. If the computer looks at your steering angle and then the yaw sensor tells it the car is turning through the corner less sharply than it should be for that amount of steering lock it thinks, 'uh-oh, that's understeer'. Then it telegraphs the centre differential and tells it to make sure more torques are going to the back axle so that the front stops dragging the car wide, like a front wheel drive car would. But then, as the car leaves the corner it tells the centre diff to push more torques forward to pull the car out of the turn without oversteering like a rear wheel drive car would. Hmm, yes, that sounds about right. Ah, and the active rear diff helps you out in sudden changes of direction so that if the car is looking like it might spin, the computer can step in and push torques to one wheel to push the rear of the car back on line. And all this computer thinking and moving of torques can happen in milliseconds. It's very clever. It's also made my brain hurt."

So, that's that explained then.

http://www.bbc.co.uk/topgear/thisweek.shtml