I’ve driven this very car numerous times over the last three years or so, from when it was sporting the m380 kit in October 2016, through the m400 upgrades (and a change to a matt black wrap) in 2018, and here I am again, about to jump in M666 FRS once more. Only this time I’m more excited than ever… Why? Because the guys at mountune have unleashed a bit of an animal with their latest upgrade, the new big-turbo m520 MRX…

Before I even set foot in the car, I’m bombarded with enthusiastic reports from all of the mountune team who have been lucky enough to drive it. Their reactions all portraying a real sense of excitement and genuine fondness for this fast Focus. So, is it really that good…?

It’s even better! Let’s not beat about the bush here, the m520 is truly awesome. It’s without doubt the best tuning package for the Mk3 RS I’ve driven to date. And it’s already up there as one my personal favourite fast Fords.

It delivers everything an RS should. It’s fun, frantic, and handles brilliantly (more on that in a second), but crucially it now also has that added ingredient that’s been missing in some modern fast Fords – the fear factor. Make no mistake, the m520 MRX is a savage beast, and if you take your eye off the ball it will try to kill you! One of the biggest criticisms I hear about modern fast Fords is that they aren’t as exciting as the older retro models were (which, personally I think is a load of rubbish anyway!) but I challenge any old-school Cossie or RST owner to have a drive in the m520 and not enjoy it. You can’t help but be impressed.


And this car is made even more impressive by the addition of KW DDC coilovers (which actually ride much better than the standard car and are an absolute treat when you start to lean on them hard) and mountune’s new 6-pot big brake kit (which are pull-your-face-off ferocious when you want them to be). These, combined with the m520 power kit make for one of the most enjoyable and exciting fast Fords I’ve ever had the pleasure to drive.

It’s not just about the big numbers either. Yes, 520PS and 700Nm is a lot, even by today’s standards. But that’s not been the objective here, and those headline power figures are merely a happy by-product of a very well-engineered power upgrade that delivers throughout the entire rev range. What mountune set out to produce was an RS that delivers an exhilarating experience as well as exceptional levels of power and torque.

The key ingredient in hitting this objective is the clever choice of Borg Warner EFR-7163 turbocharger. A quick-spooling unit that gives the RS a real punch – just check out the power graph; at 3,000rpm it’s already making 400Nm of torque (which is already most of the standard car’s 470Nm peak) which rapidly shoots up to over 700Nm by 4,000rpm! It’s this relentless shove that makes the m520 such a thrilling – and often scary – machine to drive.

Oh, and as well as being thrilling and scary, did I mention how addictive it is too? That kick up the backside never tires, and it’s frightening the way in which this car gathers speed. It can catch you out if you’re not careful, and I confess I found myself hitting the rev limiter a few times as the car simply gathered speed faster than my brain could compute.

Which brings me to another point about the m520; it’s robust. At these sorts of power levels you simply can’t expect the standard engine components to cope, so the m520 MRX upgrade does require other hardware upgrades as well as strengthened internals too. There will be people who point out you can get forged engine internals fitted elsewhere, often for less than the £4,750 mountune’s fully-fitted forged internal upgrades costs. But for the added peace of mind, personally I’d opt for the quality Carillo rods and Mahle pistons in the mountune kit, as you know they have been extensively tested to work with the m520 package. And while I can’t comment with any authority on other combinations, I can tell you with 100% confidence that I gave mountune’s m520 demo car plenty of abuse during my time behind the wheel, and it just lapped it up all day long.

In fact, the only thing that stopped my fun was when the fuel light came on (it’s surprisingly easy to empty the tank when you’re having fun) and I had to head back to mountune HQ as I realised I’d left my wallet in my car and had no way of paying for fuel! That gave me the perfect opportunity to actually drive the m520 ‘normally’, something that up until this point I hadn’t really considered (well, with so much oomph on tap why would you?). And at town speeds, or cruising on the motorway it really isn’t that different to the standard car, certainly no different to my own m400R version.

I suppose this particular car, with its savage power, sublime handling, and ferocious brakes has taken things a bit too far for the everyday driver – although the car is still perfectly capable of it, I suspect most owners who are prepared to take the upgrades this far are going to want to get the most out of them on weekend blasts, epic roadtrips, and the odd track day. And, for me, that’s exactly what the m520 delivers. You can really get hold of it by the scruff of the neck and throw it about – indeed I actually made myself feel quite sick at one point trying to get airborne for the photos! But boy does it make you feel alive. It’s incredibly rewarding to pilot, but you can’t deny there’s the constant threat of ‘if you mess up, I’m gonna hurt you’ looming over you. Of course, you can drive the m520 normally, but you won’t…

There appears to have been something of a sea change at mountune recently, with Ford no longer endorsing any tuning packages it’s almost as if mountune have shaken off the shackles of producing OEM-restricted products to show just what crazy creations they are really capable of, while all the time retaining that reassuring high-quality that mountune customers have come to expect. Alongside the m520 MRX, there’s also the torque-monster m450 MRX big turbo upgrade for the Mk3 RS, and even a new big turbo kit for the Fiesta ST too.

Oh, and if the 513bhp, 516lb.ft m520 MRX isn’t quite enough, they have recently tested another RS engine with an even bigger turbo (EFR 8374) and different cylinder head that produced a staggering 684bhp and 566 lb.ft on the engine dyno. I love this new-look mountune!


In the kit

M520 MRX

mountune ni-resist cast turbo adapter, V-band sports cat downpipe, mountune configured Borg Warner EFR-7163 turbo, gasket set, hose clamp set, turbocharger oil inlet hose, hardware kit, inlet and outlet turbo water supply, tube adapter, turbo oil drain, oil return, mountune 5-ply compressor outlet and inlet silicone elbow hoses, Xtremedi uprated fuel pu0mp, performance camshafts and valve train, oil and filter change

Cost: £6495 (supply-only), £8195 (fully fitted)


Also needed:
Upgraded intercooler, mtune handset, mountune full intake, 3in inch exhaust, hardpipe, forged engine internals




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