Given the MX5 chassis's ability to easily handle more power, it's no surprise that the little Mazda has been the subject of a lot of aftermarket power-up tuning. We've seen MX-5s sporting anything from an owner-fabricated cold-air induction set-up to mega-buck Japanese off-the-shelf turbocharger kits. No matter what the budget or power goal, it's likely there's something to suit...
The Low Cost Basics
Air Intake
In the original 1.6-litre MX-5s, the air intake arrangement appears particularly restrictive. There's a small diameter snorkel (incorporating a resonant pipe) feeding the lower section of the airbox and there's a right-angled bend into the airflow meter that is particularly nasty in terms of flow. The vane-type airflow meter also causes considerable restriction. Note that induction air is all sucked from within the left-hand side of the engine bay.
Reasonable flow improvements can be made by fitting a larger diameter snorkel into the airbox, but - really - you'll find bigger gains by getting rid if the top section of airbox. This invariably calls for an adapter and a pod filter (complete with heat shielding) or an off-the-shelf intake kit (such as the Loch Stewart airbox at http://www.miata.net.au/loch.htm).
Note that the airflow meter can also be swapped for a less restrictive, larger one from a '86 - '88 RX-7 - but it does not fit the standard MX-5 1.6 airbox and some detailed electronic changes are necessary.
In 1.8-litre models, the intake is reputedly not as restrictive as in the 1.6s. The top of the airbox was significantly improved and a hotwire type airflow meter employed. Still, gains can be found by improving the airflow into the lower half of the airbox (by fitting a large diameter snorkel) and we believe the Mazda hot-wire airflow meter is fitted with two wire mesh screens - these can be plucked out for an easy potential improvement in flow.
In many instances - and depending on other mods - a free-flowing cold air intake will give a MX-5 around 5 percent more power and improved throttle response.
Exhaust
Reducing the backpressure of the exhaust system (downstream of the factory extractors) is essential for making good power. Depending on the model and depending on your selected pipe diameter and choice in cat converter and muffler(s), you can enjoy a power improvement in the vicinity of 5 percent.
Note - to keep exhaust noise and 'rasp' to a minimum you should fill the rear muffler cavity with the largest free-flow aftermarket muffler possible.
While changing the exhaust, many owners also swap to an aftermarket set of extractors. Depending on design and the rest of the exhaust system, an extractor/exhaust combo can give around 10 percent more power - most of this being a top-end gain.
Rolled together, the usual bolt-ons - air intake, extractors and exhaust - can give a total power increased of around 17 percent on 1.6 and 1.8 models (claimed).
Other Tricks...
Another cost effective mod - it's free actually - is to alter ignition timing. Many owners of first generation MX-5s suggest going from the standard 10-degrees advance angle to a more aggressive 14-degrees advance. This improves throttle sharpness, drivability and can also give a top-end power gain - note, though, you may need to fill with high-octane unleaded at all times to avoid detonation. This mod is said not to have much effect on second generation vehicles, which use a knock sensor.
Once a MX-5 has been fitted with an aftermarket intake, extractors and exhaust system there is some scope to pick up extra response, torque and power with revised fuelling and timing. A custom chip can be burnt for some models, but the common approach is to fit an interceptor device (such as a UniChip) or a replacement ECU. Link, for example, have a plug-in programmable ECU replacement that allows you to also get rid of the relatively restrictive airflow meter. Link products are available in Australian through AVO (Advanced Vehicle Operations), as mentioned below.
The gains associated with altered fuelling and timing very much depends on existing modifications and the as-is tune of the car. In almost all instances, however, you can expect improved response and greater torque throughout the rev range - the factory air-fuel ratios are quite rich.
Serious Power-Ups
The most common approach to extracting 50 or more percent extra power from an MX-5 is to fit a turbocharger; the B-series engine is factory proven very compatible with an exhaust driven huffer.
One of the most popular turbo kits in Australia is produced by AVO.
Avalable is a Stage One turbo kit for 1.8s (for a 80 percent increase in power) and you can go all the way to a Stage Three off-the-shelf kit capable of invigorating your Mazda with a massive 140 percent power increase! Stage One prices start at approximately AUD$5200 and Stage Three runs to over AUD$7000.
All kits come complete with an AVO bar-and-plate air-to-air intercooler, cast alloy intercooler pipes, a ball-bearing Garrett turbocharger, stainless steel heat shielding, auxiliary fuel and ignition retard computer with plug-in loom, 92 site computer controlled extra injector, K&N air cleaner system, 2.5-inch stainless steel dump pipe, all fittings and hoses. A Link engine management system, a bigger turbo and injectors and other options are also available.
For 1.6s, you can go all the way up to a Stage Three turbo kit, which lifts rear-wheel kilowatts from 55 to 152 (as measured on a DTS chassis dyno) on a relatively mild 13 psi of boost! Again, you get a bar-and-plate 'cooler, cast alloy plumbing, Garrett roller-bearing turbo, stainless heat shielding. You also get a programmable Link management system, 440cc injectors, upgrade fuel pump, adjustable fuel pressure regulator, K&N filter, 2½-inch dump pipe and an optional 2½-inch exhaust system.
AVO can be contacted on +61 9584 4499 or visit their website at AVO Performance.
Another turbo kit for late-model MX-5 1.8s is offered by South Australian company, MiataSport. For around AUD$11,000 including fitment, you can treat your Mazda to a Garrett roller-bearing turbocharger, manifold, intake, exhaust, intercooler, programmable management, upgrade clutch and more. With 12 psi being pushed into a 1.8-litre mill, you can expect 150kW at the back wheels (on a Dyno Dynamics chassis dyno). And that's with brilliant drivability and assured reliability.
MiataSport can be contacted on +61 8 8443 8299.
Japanese aftermarket giant HKS also has a turbocharger kit suited for the second-generation 1.8 MX-5s. The kit includes a cast exhaust manifold, HKS T25G turbocharger, dump pipe, a piggyback Mini F-CON computer and a crossover pipe into the throttle body - no intercooler, curiously. You'll need to add your own 'cooler, high-flow exhaust and air intake to 'properly' finish the job. With everything in place, you can expect around 123kW at the wheels (on a Dyno Dynamics chassis dyno) on up to around 6.5 psi boost; a tidy 50 percent power gain over a 106kW-spec 1.8.
BD4s Service Centre - +61 2 9879 3322 - is an Australian HKS agent.
Note that we have heard of some supercharger kits for MX-5s (produced by Jackson Racing for example), but it doesn't appear there are any presently sold in Australia.
If you're not interested in forced induction, you're fairly limited.
Using traditional hot-up techniques - head work, bigger cams and a bit more compression - you might find up to 20 percent more peak power with the appropriate management changes, but it's quite likely the bottom and mid-range rpm torque will suffer to a degree. This isn't a huge concern for a free-spinning circuit racer, however.
BD4s stock HKS camshafts, adjustable sprockets and more to suit '5s.
If you want to get really creative, why not look at slipping in a different engine? The MX-5 has been forced to swallow everything from rotaries to Lexus V8s. How much do want to spend?
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