Renowned for its mk3 supercharger conversion, the Lincsbased tuner has many other strings to its bow
Best known in MX-5 circles for its 300bhp supercharger conversion for the mk3, Corten-miller puts great store in thoroughness and exceptional quality tuning work Brett Fraser
For a second or two, we’re caught off guard. From behind us comes a slightly sinister snarling and whooshing sound, reminiscent of a wild animal, and it startles us. There is, however, nothing to worry about. It’s just Corten-miller’s mk3.5 demonstrator being backed into the workshop by the family-owned company’s Sales Director, Tom Cortenmiller: the primal soundtrack is courtesy of the engine’s Rotrex C30-94 centrifugal design supercharger hungrily sucking in air and compressing it, and while the Rotrex blower is one of the quietest available, when it sneaks up on you the noise is quite menacing. Menacing in a good, strangely exciting way.
This is the very car that we at Total MX-5 drove back in our Winter 2016/17 issue. Managing Editor Bennett, our man behind the wheel for that test, was much impressed by the Cortenmiller supercharger conversion, which in the case of the demo car produces 300bhp. Yes, it’s true, we’d all be pretty stoked to be driving a mk3.5 with 300bhp under the bonnet, but it wasn’t just the 85% increase over the standard power output that Bennett found so appealing, it was the quality of the installation.
As he said at the time: ‘The biggest compliment that can be given to a modified car is to liken it to driving a standard factory machine. And that is exactly how the Corten-miller supercharged MX-5 feels.
There’s no lumpy idle or strange blips in the power delivery. The idle is rock steady and the clutch, despite being stronger, is still easy on the leg. What is different, however, is the power delivery and how it’s delivered.’
To date Bennett has been the only one of us to visit Cortenmiller, so we’ve decided to rectify that situation with a daytrip out to the flatlands of Lincolnshire. Much like the countryside of the Suffolk/norfolk border where several of the Total MX-5 team are based, CM’S Friskney headquarters – north of Boston and south of Skegness, right out on the east coast – isn’t really
on the way to anywhere, so it has to be your final destination and not a place you pop into on a journey elsewhere. Which means you have to have a rock solid reputation for quality in order for non-local customers to make the effort to come.
Amusingly, most satnavs conspire to make the final leg of the trip more taxing than it need be. Rather than taking you along the obvious route, the
A52 between Boston and Skeggers, you’re diverted across the Fens and over narrow roads surfaced like a rumpled duvet. Only harder. And with bigger pot-holes. In our somewhat poorly suspended mk1 we have to weave around as though we’re steering through invisible cones to miss the worst of the creases and crevasses, occasionally emergency braking for bigger obstacles. Keeps us on our toes…
When we regale Tom Cortenmiller with this tale he just laughs. ‘Most satnavs seem to believe that that’s the quickest way here, even though there’s a main road very nearby,’ he tells us. ‘On the other hand, we’ve sold a lot of our suspension kits by getting customers to nip back along those fen roads in one of our demo cars to compare against their own.’
The Corten-miller family has always lived locally, and the performance tuning business was set up by Tom’s father, John, in 1979. ‘Next year will be the 40th anniversary of my father establishing his workshop on the same site that we’re still on,’ Tom explains. ‘Back then he was preparing rally cars, plenty of mk2 Escorts, and he was into high performance cars all his life. Sadly he passed away in 2004, but both my brother Ben and I inherited his car-loving gene. Ben has always been in the car industry, and although I went away to university to study business information technology, it wasn’t too long before I was back here. Our mother, Lynette, works here, too, as managing director.’
Although CM is known amongst enthusiasts as a national tuning outfit, it’s also run as a local garage. ‘There are two elements of the business,’ reveals Tom, ‘the tuning operations and the servicing and MOT side. With the latter we cover about a 30-mile radius from here and it brings us in a good, steady flow of work.’
Sure enough, on the day of our visit there’s an elderly Mitsubishi Shogun in for attention, and a Porsche
Boxster up on one of CM’S three ramps that’s having a cooling issue sorted. But there’s also a very serious-looking Honda Civic Type R race car gracing the workshop, together with an immaculately restored and uprated mid-engined Renault Turbo 2 rally car. ‘Despite what it might look like today, we don’t really do much motorsport prep,’ reveals Tom.
‘However, the Civic represents the absolute peak of what we’re capable of here. We’ve taken it from a standard EP3 Type R into a 500bhp frontwheel drive beast that competes in the Civic VTEC Challenge and have done everything ourselves bar the
painting. We also provide support at the race meetings.’ Even if you’re not a great motorsport fan, spend a few minutes examining the standard of workmanship on this car and you’ll have no hesitation in handing over your own road car to CM for a few upgrades.
‘We’ll tackle pretty much anything from, say, a set of uprated springs and dampers, to a full-on high performance conversion with an extreme and bespoke specification,’ says
Tom. ‘In support of this we have our own dedicated cylinder head shop and engine building facility, a Hunter suspension alignment machine, and we also have, in its own purpose-built room, a Dyno Dynamics rolling
road with four-wheel drive capability. And critically, in this age of advanced electronics, we have Toby, our full-time ECU calibration engineer.
‘We work mainly on German and Japanese marques, and the latter, of course, includes the Mazda MX-5. That said, we’ve never been much involved with the mk1 or mk2 models: because of their age, you can start working on one element of them, the brakes, say, and then uncover a whole other can of worms in the process. They’re wonderful little cars, don’t get me wrong, but they’re best left to the guys who specialise in them. The way we prefer to work is to give our customers a fixed price to carry out a supercharger conversion on a mk3, for example, where we have a pretty good idea of how much work is involved – including installation and VAT it’s £4995 for the Kit Pro 230250bhp conversion, £6195 for the Kit Club Sport 280–300bhp version. With the older cars you keep finding more problems and the price keeps going up: it can be upsetting for customers on a tight budget, and from our perspective can unexpectedly tie up one of the ramps, preventing us from getting on with other jobs.’
But that’s only part of the reason that CM picked the mk3 for its supercharger conversion kit, as Tom explains: ‘Early on we realised the potential for ECU tuning, so when we were looking around for a new project we’d always look at a car’s ECU and work backwards from there. We wanted to access the ECU and tune inside it, rather than develop a piggyback system, and the mk3 MX-5 gave us that capability directly through its diagnostic port: in some ways I still find it incredible that you can tune a car in this way.
‘And the rest of the mk3 is a great platform to work on. Compared with earlier MX-5S it’s a proper car that drives well and benefits from little niceties such as heated seats. Sure, it’s a bit overweight, but it handles well and in standard form simply lacks enough power. In other words it is the perfect base for our supercharger conversion.’
And why a supercharger, rather than the more popular turbocharger? ‘Both types of forced induction have their pros and cons, but we think that the supercharger’s very linear power delivery better suits the character of the mk3.
‘And compared with a turbo, a supercharger has a very low thermal impact on the engine bay. We spent a long time developing and testing our kit, making it a bolt-on installation but to OEM standards, and as a consequence we’ve had no reliability issues.’
For a while, a few years back, mk3s were pilloried by some as being too big, too porky, and insufficiently like an MX-5. Values tumbled. But Tom has witnessed a change in attitudes more recently. ‘Some customers may have bought their car quite cheaply but they’re prepared to invest in it quite heavily because they now realise its potential. We find that many people don’t simply go for the supercharger kit, but they also upgrade the rest of the car, too – clutch, brakes, suspension, exhaust, wheels, tyres, etc.
‘And we can fit whatever brands a customer wants. Although we’re a supplier, and sometimes distributor, for many of the major tuning companies, we’re not tied in exclusively to any one of them, so can be flexible about specific requests for components.’
Tom sees plenty of potential in mk3 tuning. ‘Although people are starting to realise that it’s a much better car than portrayed in earlier reports, mk3s remain very good value and generally are still in good condition and healthy supply.
‘Our supercharger kit – especially when combined with some sensible upgrades of other components – turns them into an awesome little sports car. The mk4 is next on our radar.’
Corten-miller’s geographical location might not be conducive to a casual visit, but Tom and the team’s passion for top quality tuning may well mean that after a bit of phone time with them, you could be jumping into your car to make a special trip.
Corten-miller’s 300bhp supercharged demo car poses in the Lincolnshire workshop alongside a high-tech Honda Civic racer and poorly Porsche Boxster.
Tom Corten-miller, sales director
In 2019 Corten-miller will celebrate being based at its current site for 40 years. As well as a tuner, the company is a general garage and MOT centre.
CM’S reception area is comfortable and lined with temptations…
Showcased in the CM reception area is the company’s supercharger conversion for the mk3’s engine. In top tune it gives 300bhp, which is nice.
The Rotrex supercharger looks as though it might have been placed there by Mazda itself.
CM likes to make its mark on the parts it fabricates.
Polishing the pipe’s interior for swifter gas flow.
Goodies ranging from gifts to, er, ‘essentials’…
CM not tied to any brands, but does stock good ones.