How to build a 513bhp Ford Focus RS

With much of its business nowadays coming from those clever plug-and-play kits you can buy online and install yourself, which rewrite a few lines of code in your car’s computer to give it more go, it’s easy to forget Mountune has been building and supplying racing engines for some 40 years. Mostly for Ford, with which it's won a tonne of races and rallies. It’s that expertise that’s helped it develop this – a Focus RS with an astonishing, outrageous and totally unnecessary 513bhp and 516lb ft. It’s called the M520, and it was announced last August.

Mountune didn’t set out to build a 513bhp Focus, says boss Alec Pell-Johnson. His company already offered kits for the Focus RS giving more modest power increases, but then customers started asking for MORE. And Mountune knew that, thanks in part to colleagues in the US, that with the right changes to its internals the Focus’s 2.3-litre turbocharged engine could take it.

“We initially thought if we do ten this year [2019] that’ll be great. But we sold the first ten in about a month,” Alec tells us. “A lot of the guys are going from standard, which is an enormous change. Also an enormous amount of work.” The upgrade costs over £15,000 including labour and takes Mountune’s mechanics about a week – less on both counts if the car’s owner already has some of the right kit installed.

The techs usually pull the engine completely out of the car, before stripping it down and fitting the stronger components it needs to make supercar-power. “We source those parts from our race engines. And we already knew they could handle the power, because they run in the BTCC,” says Alec. "Quite a few of the bits are interchangeable."

The main components of the upgrade are the all-important forged internals, plus a bigger, better turbocharger with ceramic bearings from BorgWarner (the single most expensive component). Then there’s the high-pressure fuel pump and countless new hoses and gaskets, a three-inch exhaust and upgraded intake and intercooler. “You need the full air-cooling, oil-cooling, water-cooling kits,” Alec explains. “We haven’t ever had any overheating problems on ours, nor any we’ve ever done as far as I know.”

When the mechanics have finished putting the engine together and have successfully reunited it with the car itself, Mountune usually does around 500 miles of testing before handing it back to its owner, just to make sure everything’s working as it should. And said owners come from miles around – Alec tells us of a chap who drove down from an island off the northern coast of Norway to have his RS worked on, while just this year owners have driven over from Germany and Romania.

We were all set to have a go in Mountune’s development car, then lockdown struck and delayed our plans. But worry not, the TG review is coming.