Total MX-5’ s UK road test
The mk4 has always felt like it could handle much more power – thanks to a turbo, BBR has now given it a stonking 250bhp. It’s impressive
The normally-aspirated, high-revving ethos that comes standard with every MX-5 since its inception has always been the roadster’s double-edged sword. On the one hand a revvy, aspirated engine that demands to be worked hard is a fundamental part of the MX-5 experience, one made sweeter by the sweetest and snickiest of manual gearboxes. On the other hand, though, it’s merely quick, rather than actually fast, accentuated by the peaky nature of a 16-valver lacking in torque and delivering its peak well past 5000rpm.
Don’t get us wrong, Mazda was absolutely right to give the MX-5 a zingy NA engine, and for most folk it’s just fine and those occasional journeys to the redline are all part of the MX-5 vibe. But it is rather onedimensional and flat when you’re not on it, and sometimes being ‘on it’ is a bit too much like hard work. The road isn’t a race track, where you can consistently keep the engine buzzing at peak torque and power. In fact, for the road ‘torque’ is the operative word. It’s why our little MX-5S get seen off by all those mundane turbodiesels. Everyone these days has a big wodge of turbo torque bang in the mid-range and unless you’ve got your 16-valves dancing out of the bonnet, you’re left behind in a puff of soot.
Mazda knew that it wouldn’t take long for the mk1 MX-5 to be fitted with a turbo. Indeed they positively encouraged it, equipping it with an engine that was
The one we’ve been waiting for: BBR’S Stage 1 turbo conversion turns the mk4 MX-5 from a merely quick car into something genuinely fast with Porsche-busting pace
surprisingly low in compression for a normally aspirated unit (so that it would run happily on low octane fuel). When BBR developed a turbo kit for the mk1 in 1990, it did so with Mazda’s blessing, assistance and a warranty. The addition of a turbo transformed the MX-5 from fun to fast. I’m old enough to have experienced that first press car in 1990 and was struck by how dramatically the character of the little Mazda had been changed. It offered choices as to how you wanted to proceed. Fast and frantic or fast and relaxed. The choice was yours. I loved it...
And of course BBR has been at the forefront of MX-5 turbocharging pretty much ever since, which is why we’re back at Brackley to drive the hugely anticipated turbo mk4. And here’s progress for you: back in 1990 the BBR mk1 Turbo MX-5 packed a 150bhp hit. For 2017, the turbo mk4 bangs out a fulsome 250bhp and weighs approximately the same.
The original red mk1 press car stars on the wall in the reception area at BBR’S workshop, situated bang next door to the Mercedes F1 team. I mention to chief engineer, Neil Mckay, that I drove the very same car 27 years ago, which immediately makes me feel very old. Racking my brain as to the last time I’d been at BBR, I realised it was probably to drive one of its turbo Lotus Elises and before that there were the modified Sierra Cosworths. Cue a trip down memory lane and maxing one of BBR’S fearsome ‘Mogul’ conversions on Bruntingthorpe proving ground’s twomile straight at 180mph...
But enough of the reminiscing. Back in the real world there’s work to be done. The Turbo MX-5 mk4 has been a long time coming. Indeed, we were anticipating a first drive way back in Sept 2016, when we were putting together the first issue of Total MX-5. Why the delay? Well, while the hardware side of things has been pretty straightforward, the issues have all surrounded infiltrating and manipulating the mk4’s complex engine management and connected software. Throwing the standard ECU away and starting again would be throwing the baby out with the bathwater. Much better to try working with the standard system and take advantage of Mazda’s expertise and 1000s of hours of development. To that end BBR worked with ecutek to create a turbo map within the standard ECU, supplying the ECU guru with a kit to work on for its own mk4 MX-5. It may have taken a while to master the standard system, but it has been worth it.
Electronics aside, the rest of the kit is about hardware. The 2.0-litre SKYACTIVG engine is left alone internally. It will happily handle the extra power and torque. The heart of the conversion is a surprisingly large twin-scroll turbo mated to BBR’S own inlet manifold. A twin-scroll turbo is rather like a two-inone turbo with two exhaust gas inlets and two nozzles – one for low-rev, quick response and the other one for peak performance. Without wishing to get too techy, the twin-scroll turbo works in tandem with a split-exhaust manifold, which channels the turbo pulses between the cylinders in a rather more efficient and precise manner. Most modern engines use the twin-scroll system now and it’s largely responsible for the near elimination of turbo lag and turbo engines being able to run a higher compression ratio. Or in the case of the BBR conversion, the mk4’s standard compression ratio of 13:1. The twin-scroll turbo also works well with Mazda’s 4-2-1 exhaust manifold developed specifically for the SKYACTIV-G engine to overcome the marginal exhaust restriction of a catalyst close to the cylinder head.
Cooling the charge air going into the
engine is an air-to-air intercooler and associated pipework. Peering under the bonnet, the effect is of a factory fit. The turbo sits neatly on the left-hand side of the engine, under a carbonfibre shield. The intercooler is positioned in front of the radiator.
Power – as we’ve intimated – is 250bhp, which equates to 234bhp per tonne. To put that into perspective, a Porsche Boxster with 300bhp has 213bhp per tonne. More tellingly, though, is the torque figure – 236lb ft at 3800rpm, compared with the standard car’s 152lb ft at 4950rpm. And a wholesome 200lb ft is available between 2750rpm and 6500rpm, against the standard 148lb ft. You don’t even need to get behind the wheel to know that sort of torque curve is going to make itself felt and indeed transform the character of the car. But get behind the wheel we must, so let’s get going.
BBR has used a Recaro Sport Edition as its demo car. A good choice because it comes with Bilstein dampers and the Recaro seats are a real cut above the standard perches. BBR has added its own progressive springs to the suspension mix and slightly wider OZ Ultra Leggera wheels booted up with 215/45 x 17in Yokohama tyres for a bit of extra grip. Not a bad idea with the extra oomph on offer. This car is now also being used to develop the Stage 2 300bhp kit and so has a slightly stronger, grabbier clutch: the standard clutch happily handles the 250bhp and extra torque of this Stage 1 setup.
An MX-5 with 250bhp and a mass of mid-range is indeed a very different animal but it doesn’t actually feel typically turbocharged. The twin-scroll turbo, combined with the standard high compression ratio, means there’s next to no lag at low revs. It just feels like the standard engine. Conversely that means that it will also happily rev round to 7000rpm. It’s what occurs in between that’s significant, as the above figures testify. On the road that means a subtle rush from the turbo and a not so subtle rush of power.
It’s not like an old school turbo – all and then nothing – it’s smooth, linear and large. And while it will rev to the red, there’s very little need to go there, as the torque curve suggests. And strangely, perhaps, it suits the chassis well. It’s still not a car that likes to be hustled, and if you really start to stamp on things it will (just like the standard car) get ragged and lose its shape. Sure it will showboat, but it rewards smooth inputs, only now there’s more to play with and different angles of attack to explore and more to exploit. The extra rubber means you can get the power down and the limited-slip diff has more work to do, but it can be relied on to efficiently shuffle the power between the driven wheels for some easily provoked slides. The simple addition of BBR’S own springs has wiped out the mk4’s inherent wobbliness and roll, with added control and no loss of ride comfort. A rare trick when it comes to modded suspension and, at £495 fitted with a geometry set-up, worthwhile for any mk4 MX-5.
Any downsides? Not really. It depends, really, how vital you feel a high-revving, naturally aspirated engine is to the MX-5’S appeal and how you feel about modified cars in general. Certainly there is very little ‘tuner’ about this conversion. It’s as much ‘factory’ as you could possibly expect and incorporates all the standard car’s safety functions and dayto-day mapping and functionality.
Speed costs, of course, and here’s where you start paying. If you want to go big, then you can buy a BBR turbo modded MX-5 brand new for £29,995, with a three-year warranty. Is that expensive? Not when you consider that a Fiat 124 Abarth Spyder costs the same, but with a mere 170bhp from its 1.4-litre turbocharged engine.
At the other end of the spectrum you can get a DIY fitment kit for £4395. BBR assures us that it’s an OK job if you’re reasonably adept with the spanners: it would be fun to find out. Alternatively you can take your car to BBR, or one of its approved fitting partners, and get the job for £4995. There are other costs, such as the springs, which we would certainly go for, and the option of four-pot or sixpot Wilwood brake calipers at £595/£895 respectively. In the great scheme of things, and for the power increase, we don’t think the pricing is outrageous. Indeed it’s still very much in keeping with the MX-5’S affordable sports car mantra. Oh, and there’s a kit on the way for the 1.5-litre mk4, which promises 210bhp–220bhp, and BBR is developing Heritage Turbo kits for the mk1 and mk2, which we’ll be testing in the next issue.
So would we buy one? Should you buy one? For us, if the stars aligned and we found ourselves with a mk4 MX-5, perhaps secondhand, at a reasonable price, with some man maths, then yes. Mk4 2.0-litre cars can be found at around £17,500. Go on, do the sums... Tempting, isn’t it? And if you’ve already got a mk4? Oh, you’re already on BBR’S website and you now appear to be picking up the phone. Our work here is done.
Quite aside from packing a 250bhp punch, BBR’S demo car looks just right on its slightly lowered suspension and wider rubber Below: Wilwood four-pot calipers hide behind OZ wheels Below right: Recaro option seats worth every penny
Right: installation could pass as factory fitted. Dual-scroll turbo sits under carbonfibre heat shield Left: test car is fitted with slightly wider Yokohama rubber and OZ wheels, plus BBR’S own spec springs, which work a treat with Mazda’s optional...
This is what you get for your £4395
The graphs tell the story – 248bhp and 236lb ft of torque, and a commendable 234bhp per tonne
CONTACT: BBR, Unit 1, Oxford Rd, Brackley, Northants NN13 7DY 01280 700700 www.bbrgti.com