Yesterday was a memorable day for me. Not only did I get to test drive the new, most powerful production Subaru Impreza, but better still I got a behind-the-scenes tour of the premises of the company responsible for it.

If you don’t know it, Cosworth is one of the world’s foremost high-performance engine builders. Its racing engines are legendary; only Ferrari has powered more race-winning F1 cars.

Read Matt's first drive of the new Cosworth Impreza STI CS400

As part of the tour I saw Cosworth’s current F1 units – 2.4-litre V8s – being assembled in a room the size of a typical school classroom – but a fair bit cleaner and more orderly.

The precision required to put these engines together is mind-blowing. They’re so tight that they’re seized when cold; you have to warm them through with hot oil before they’ll loosen enough to start. The valve springs they use are not much bigger than ball bearings, and yet at close to 20,000rpm, they compress 300 times a second. And a fully dressed engine weighs 90kg.

At the other end of that room, 7.3-litre V12s were being assembled for Aston Martin’s One-77 supercar. Cosworth was a little unwilling to talk about these more than to say that they’re ‘very special’. Most of the engine building it does is necessarily covert.