Mountune m520 Review: What It's Like To Drive A 516bhp Ford Focus RS

With the power war finally showing signs of waning a little, we can probably agree what constitutes a sensible power output for a certain kind of car. A supercar? Let’s say 600 - 700bhp. For a sports car, 350+ seems about right, and if it’s a sports saloon, we reckon at least 450bhp.

For hot hatches, I’d be tempted to peg the figure at around 300bhp, although the third-generation Ford Focus RS went a little beyond that. With 345bhp, it gave ridiculous bang for buck in its initial sub-£30k guise. 345bhp is surely more than enough for anyone. That didn’t stop the tuners, of course, and we weren’t surprised by the kind of power packs that came out. Until that is, Essex-based outfit Mountune - famed for its work on Fords - went and punted the 2.3-litre Ecoboost engine beyond 500bhp.

It’s made possible with the m520 kit, and it brings the 2.3-litre inline-four turbo to 516bhp, although Mountune says, in reality, the figure is “probably a bit more”. The key part of the upgrade is a BorgWarner EFR-7163 ceramic ball bearing turbocharger, but in order for the engine to take the boost, much of it has to go.

The standard block and head are retained, but little else is carried over. We’re talking new con-rods, pistons, camshafts, valves - the works. This already sounds a bit spendy, before you consider items like the high-pressure fuel pump from Xtreme-DI, which is £1600 on its own.

The result is, Mountune tells us, essentially a “full-blown race engine”. It’s over-engineered, and that’s reflected in the price. Get all the work done, and you can expect your bank account to be missing around £15,000. Sounds like an extremely niche conversion, but the company is currently building one of these a week. So what are these clearly unhinged customers letting themselves in for?

The answer is something that’s… full on. The m520 is monstrous. Feisty. Overpowered. And above all, outrageous fun.

You have to remember that Drift Mode is a bit of a party trick - what the Focus RS has is still a front-biased all-wheel drive system. The half-shafts are piddly, and as such, not much torque can go to the back wheels. So that means the vast majority of the m520’s 516lb ft delivery goes the way of the front wheels.

Under power, the torque steer is violent. The front end seems to have a mind of its own as it’s clobbered by Mountune’s bonkers engine. You have to make sure you’re on a nice, straight, clear and relatively flat piece of road before you even think about fully depressing the throttle pedal. Between 3000 and 5000rpm is when the thoroughly reworked 2.3 really comes on song, hurling the hatchback forward with viciousness. It’s far scarier than plenty of cars I’ve driven with much more power - wheelspin in first, second, third and - depending on the conditions - fourth gear can be expected.

Turbo lag is not as bad as you might expect, with response helped by the turbo’s ceramic ball bearings - it’s not something that takes an age to spool up. You do need to be at 3000rpm or higher for the exciting stuff to happen however - this RS won’t do a whole lot below that mark. Above that, prepare for some outrageous pops and bangs from the exhaust. It’s brilliantly rude.

Even before you start ploughing excessive amounts of power through the m520’s bewildered front axle, there’s a lot more life to the steering. The KW Clubsport coilovers of the demo have stiffened up proceedings nicely, yielding a nice bit of kickback in the steering. Despite the added firmness though, there’s a suppleness to the damping that means the m520 is quite comfortable. Well, it would be if it wasn’t for the weirdly hard seats, but we can blame Ford for those.

You will often find yourself switching to a more sedate style of driving (where you’ll find the Asbo-spec exhaust doesn’t drone at all), as piloting the m520 at a decent pace isn’t something you’ll be able to keep up for long. You can’t get into a rhythm with it on a twisty bit of road, and the right-hand pedal soon becomes something you’re wary of.

If it was me, I’d go for one of Mountune’s less bonkers tuning packs for my ideal Focus RS. I’d be after a car that can put its power down with a little less drama. But that’s the thing - Mountune fully accepts that over 500bhp in one of these is excessive and downright crackers, but it went ahead and did it anyway for the few customers who value power over everything. People who’d part with the price of a tidy used Porsche Cayman simply as their RS has to be the fastest.

The m520 is a reminder - a reminder that we love the tuning world precisely because it often doesn’t make sense.