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Mazda MX-5 SP Turbo

The MX-5 to light your fire!

Words by Michael Knowling, Pix by Michael Knowling, Julian Edgar and Mazda Australia

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This article was first published in 2002.
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It's been more than ten years coming, but at last the Mazda MX-5 has power. R-e-a-l power!

The newly released MX-5 SP is bursting with an amazing 39 percent more power and 60 percent more torque than the standard MX-5; it's more than enough to transform the SP into a fully-fledged, drop-your-jaw rocketship.

So where does this incredible power and torque explosion come from, you ask?

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Well, the MX-5 SP (Special Performance) uses a turbocharger kit that's exclusive to the Australian market. Local aftermarket go-fast companies were handed the job of developing the kit under direction of the Sydney-based Mazda Motorsport Division.

The SP turbo kit is built using the standard 1.8-litre MX-5 engine as the platform. The engine requires no internal modification - inside, it remains completely standard, from its variable cam-timed 16-valve head to its 10.0:1 compression ratio.

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Because of this high static compression ratio, turbo boost pressure must be kept relatively mild; the selected Garrett ball bearing turbo is set to produce only up to 8.0 psi boost. Mounting the turbo to the BP's cylinder head is a purpose-cast nickel-alloy manifold, and - like most modern turbochargers - the turbo's centre bearing is water-cooled and engine oil lubricated.

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Once the SP's induction air is compressed by the turbo, it passes through a large front-mount tube-and-fin air-to-air intercooler. A recirculating Bosch blow-off valve is also fitted.

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With the turbocharger forcing increased airflow through the engine, an all-new intake and exhaust was fabricated. This trick-looking carbon fibre and fibreglass airbox (with a massive bell-mouth feed) frees airflow into the turbo, while a larger diameter stainless steel exhaust lets gasses escape.

To meet the demands of the turbo system, the fuel supply and engine management systems needed to be revised. Larger volume fuel injectors are fitted for each cylinder and the standard Mazda ECU is reprogrammed to suit.

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Other upgrades along the development path include different spark plugs and a larger radiator. Interestingly, the standard MX-5's 6-speed gearbox and clutch remains untouched, as does the open-centre diff.

It's claimed that a total of 215 parts have been added or modified to create the SP - yet total vehicle mass has risen only 3 per cent, from 1085 to 1119kg. Yes, you read that right - a power lift of 39 per cent with a weight increase of just 3 per cent...

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The result of the SP's intercooled turbo system is a quoted 157kW at 6800 rpm and 289Nm at 4600 rpm (up 44kW and 108Nm over the standard MX-5). As Mazda's advertising says, "these increases lift the most popular sports convertible to a new level of performance..."

On the road, the turbocharged SP is extremely throttle-responsive. This is backed by strong low rpm torque - it's possible to keep up with traffic by short-shifting each gear and never climbing onto boost.

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Once on boost, torque is delivered very progressively and the engine is happy to spin to its 7000 rpm redline. Boost pressure doesn't fall away after a gear change - the flow of speed continues seamlessly.

Performance times? 0 - 100km/h in just over 6 seconds and the quarter mile in low-to-mid 14s. Pretty bloody quick in our book.

Note, however, the MX-5 SP's turbo package isn't without flaws...

The Shortcomings
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One of the most worrying aspects of the SP turbo conversion can be seen in this photo - the turbine dump pipe is very, very close to one of the metal brake lines. The brake line has a thin protective sleeve around it and the dump pipe has been heat coated, but we're sceptical whether these measures are enough to give effective long-term protection from the searing post-turbine temperatures.

More of the aforementioned heat coating is also applied to the exhaust manifold and turbine housing, but we have to wonder why there are no 'proper' heat shields. Every other production turbocar that we've ever seen has at least one manifold heat shield...

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If you think the route of the intercooler pipes is ugly, things get even uglier when you look closer. As can be seen here, the intercooler pipe leading into the throttle rubs against the top radiator hose...

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Here you can see the SP has no electronic boost control system - there's simply a hose from the compressor outlet direct to the wastegate actuator. You can see the hose is beginning to perish and constrict flow near the compressor output fitting...

At light load constant throttle cruise, we also noticed the SP has a slight jerkiness. This, we are told, is a result of having to move the oxygen sensor away from its original position (ie further away from the exhaust valves). Furthermore, the SP suffers a slight flat spot on the transition to boost and there's also a jolt that occasionally occurs when coming hard off the throttle.

Oh, and the MX-5 SP produces a cacophony of noises.

The exhaust pops and bangs and a loud turbo flutter accompanies every swift gear change. Of course, these noises might excite some people but we found that even over a short time, they became tiresome...

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Despite its humongous power-up, the SP gets its grunt down exceptionally well. Using just the standard MX-5's open-centre differential, it will light up its inside back tyre when booted around a tight corner, but - overall - the extra power is effectively put to use.

With a twisty mountain pass laid out before it, the SP handles with all the finesse MX-5s have become renown for - nothing's been spoiled by the extra power.

Turn-in is precise and there's very good cornering grip from the 205/45 16 Bridgestone Turanzas. The chassis is extremely alert to mid-corner driver inputs, enabling almost mind-reading changes to attitude.

In short, the only thing altered in the SP is its ability to rush from corner to corner with tremendous pace.

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The platform for the SP's handling is a rigid monocoque chassis. In late 2001, the MX-5 design was revised to give 22 percent more torsional rigidity and 16 percent more bending rigidity. Part of this increase came from the fitment of a front suspension tower brace.

Bolted to the rigid chassis are front and rear swaybars and double wishbone suspension. The springs and dampers are carried over from the standard MX-5, so - despite its high level of performance - the SP's ride is quite supple.

The rpm-sensing power-assisted steering is wonderfully direct, communicative and nicely weighted. Our only criticism in this area is the ongoing - though only slight - steering correction required over bumpy roads.

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Curiously - despite making 39 percent more power - the MX-5 SP shares the same brake package as the standard model. This initially appears to be a huge oversight, but we didn't experienced any fade during our road test. Apparently - again, in late 2001 - Mazda equipped the MX-5 with larger brakes (270mm ventilated at the front and 276mm solids at the rear). They seem to do the trick on the SP - on the street, anyhow.

Thankfully, Mazda hasn't added any outlandish add-ons to 'distinguish' the body or interior of the SP.

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Onboard, the turbo MX-5 receives only a few token changes - alloy air vent and gear lever surrounds, a polished aluminium knob, a grippy Nardi leather wheel and new scuff panels. These extras combine with the usual MX-5 equipment list - power windows, mirrors and aerial, rear window demister, double-DIN CD/tuner (with two full-range door speakers and tweeters), remote central locking, immobiliser and dual airbags. The instrument cluster is clearly laid out, comprising a 240 km/h speedo, tacho, temperature, fuel and oil pressure gauge.

All of the SP's features are easy to operate and perform well - the only exceptions being the aluminium gear knob (that conducts gearbox heat) and the fan speed switch that's too small.

Note that air conditioning is a $2500 option, as Mazda claims "some buyers are likely to race the SP".

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The MX-5's cabin, as always, is tight but bearable. There's enough headroom and legroom for people up to around 186cm tall, but there's not a lot of space for movement. The driving position is very good and the seats are comfortable and supportive.

The MX-5's manually operated soft-top has two large grab-locks that hook the front of the soft top onto the windscreen header rail. Opening the roof is easy - release both grab-locks and lift the front of the roof back over your head. A detachable hardtop is available as an option.

Externally, there are few give-aways to the 'hot rodded' MX-5. Aside from the usual 16-inch 5-spoke alloys and fog lights, the only additions are a fatter exhaust tip, the front-mount intercooler, Mazda Motorsport stickers on the front quarter windows, SP badge on the rear and a polished fuel filler cap gracing the left flank. Oh, and make sure you only ever put 95+ RON fuel through the filler - very important to remember!

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Paint quality is excellent, but - surprisingly - panel margins are in places quite wide.

Okay, so the MX-5 SP carries all the positive attributes of the standard MX-5 and - despite the aforementioned shortcomings - offers a whole lot more zoom-zoom. The big question is, howmuchizzit?

Well, minus the optional air-con, a beastie like this will set you back $55,540 (which includes Mazda's 3 year/unlimited kilometre warranty).

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The nearest competition for the SP is the MGF VVC (for 50-odd grand) and Toyota MR2 Spyder (at around $46,000). Both of these cars are similar in size and design, but they are brutally outgunned in the power stakes by the turbo Mazda.

In performance terms, nearest competition comes from the likes of the BMW Z3 3.0-litre Roadster and Porsche Boxster S - costing about 88 and 133 grand respectively...

If your one-and-only criterion is straight-line go for the dollar, note that the current Subaru Impreza STi is almost line-ball with the SP and costs within a few hundred dollars - kinda puts things into perspective, doesn't it?!

Finally - if you are interested in purchasing an SP - make sure you act quickly. Mazda has only 100 vehicles slated for production - another batch may follow, depending on demand.

Mazda MX5 SP Fast Facts...
  • Fantastic performance increase over MX5
  • Driveable, linear power
  • Handling and ride still near-perfect
  • Not quite factory quality in the additional componentry
  • Some minor engine management stutters

The Mazda MX5 SP was supplied for this test by Mazda Australia.

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