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A Turbo'd Green NB Project

Mazda MX-5 NB (2.5)

Mazda MX-5 Mk2 (NB)

A Turbo'd Green NB Project – MX5 Nutz

Read the full write-up at A Turbo'd Green NB Project – MX5 Nutz ↗

Photo: A Turbo'd Green NB Project – MX5 Nutz

Sorting out a turbo NB Miata bought mid-build, fault by fault

ShawLovelock bought a turbocharged Mazda MX-5 NB as a cheap weekend project and spent months chasing issues left by the previous owner, from a stuck turbo actuator and brake line failure to a persistent idle droop traced to an ECU firmware quirk. Along the way he confirmed the forced actuator, radiator and a few trim parts, while rust repair and a wheel change remain on the list.

Specs

As stated in the original write-up.

Engine
Forged bottom end (Bofi Maxspeeding kit)
Turbo
TD04 19t hybrid turbo
Exhaust manifold
Kraken manifold
Radiator
M2 Motorsport radiator (Bofi), replacing a Japspeed radiator
ECU
ME221 (Gen 1)
Fuel injectors
RX8 Injectors
Fuel pump
Walbro 255 fuel pump
Clutch
Stage 4 clutch
Exhaust
Malian straight through exhaust
Suspension
Tein coilovers
Front brakes
Corrado front brake upgrade with braided lines
Wheels
OZ e30 Alpina wheels (planned for replacement)
Interior seats
SVT leather seats & steering wheel
Roll bar
5 Race Bars roll bar
Power output
Around 255whp / 300hp at the flywheel on a dyno run

Parts used

Parts named as used in the original write-up, grouped the way the Parts page groups them. Where one of the shops we index lists the same thing for this car, it is shown underneath with a link to the shop.

Engine 2

Fuel & Ignition 4

Cooling 2

  • Japspeed radiator with twin fans

    Original uprated radiator, later replaced after wear and a coolant leak

    In the shops
    Fan Switch for Lower Bypass/Radiator Pipe ↗TRGB· £10.95 GBP
  • M2 Motorsport radiatorBofi

    Replacement radiator fitted along with new hoses

Gearbox & Drivetrain 1

Suspension & Steering 1

Brakes 2

Wheels & Tyres 1

  • OZ e30 Alpina wheelsOZ

    Current wheels, owner planning to replace them

Body & Trim 4

Interior 1

Electrical 1

  • Replacement turbo actuator

    Fitted by garage after original was found stuck closed causing over-boost

Other 1

  • Malian straight through exhaustMalian

    Exhaust system fitted with a 'bung' quieting the note

Photos

14 pictures collected from the write-up, in the order they were posted, shown from A Turbo'd Green NB Project – MX5 Nutz. A picture opens larger here, with the way through to the page it is on.

ShawLovelock · 2023-02-15T04:50:23-0500 4this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Automotive parking light Car Wheel Tire VehiclePhoto: A Turbo'd Green NB Project – MX5 Nutz
Car Tire Wheel Vehicle Automotive parking lightPhoto: A Turbo'd Green NB Project – MX5 Nutz
Motor vehicle Automotive design Vehicle Automotive fuel system Auto partPhoto: A Turbo'd Green NB Project – MX5 Nutz
Rectangle Slope Font Line HandwritingPhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-02-16T12:14:47-0500 1this post at A Turbo'd Green NB Project – MX5 Nutz ↗

ImagePhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-03-03T04:59:29-0500 2this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Wheel Automotive parking light Tire Vehicle CarPhoto: A Turbo'd Green NB Project – MX5 Nutz
Motor vehicle Hood Automotive design Automotive fuel system VehiclePhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-03-03T06:23:19-0500 2this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Font Auto part Screenshot Machine MetalPhoto: A Turbo'd Green NB Project – MX5 Nutz
Motor vehicle Automotive tire Automotive fuel system Plumbing valve GasPhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-03-05T16:32:51-0500 1this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Automotive tire Motor vehicle Wood Tread RimPhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-04-06T12:50:29-0400 1this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Rectangle Slope Font Parallel PatternPhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-04-11T12:00:30-0400 1this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Wood Automotive tire Gas Audio equipment RimPhoto: A Turbo'd Green NB Project – MX5 Nutz

ShawLovelock · 2023-05-05T04:54:06-0400 2this post at A Turbo'd Green NB Project – MX5 Nutz ↗

Plant Wood Grass Rectangle GasPhoto: A Turbo'd Green NB Project – MX5 Nutz
Mesh Grille Grey Wood Road surfacePhoto: A Turbo'd Green NB Project – MX5 Nutz

How it was done

Starting condition

The car arrived with initial electrical and idle problems, which improved after replacing the battery, coilpack, leads and plugs and cleaning engine grounds. The owner listed an extensive existing spec sheet and a long list of planned work, including rust repair, wheel changes and a bigger turbo.

Early fixes and ongoing gremlins

A front numberplate bracket and a Ramair air filter were fitted. Rust repair quotes for sills and arches came in expensive, so patch repairs and over-fenders were considered instead of full replacement. A brake line failure caused loss of pedal pressure and needed professional repair.

Turbo actuator and dyno discovery

At a garage for new brake lines and a PAS belt, the dyno revealed the actuator was stuck closed, over-boosting a standard TD04 that the previous owner had fitted in place of the original hybrid unit. A new actuator transformed the car, giving roughly 255whp and smoother, more controllable boost.

Cooling trouble and radiator replacement

Shortly after, the coolant tank ran dry with a suspected leak near the intercooler piping. After weeks of rain delaying diagnosis, a new M2 Motorsport radiator and hoses were fitted, replacing the worn Japspeed radiator, restoring reliable running.

Idle fault resolved by remapping

A long-standing idle droop under electrical load was eventually traced to a firmware limitation in the Gen 1 ME221 ECU. A remote tuner supplied a revised map that stabilised idle using ignition timing, though a full Gen 2 ECU upgrade was ruled out on cost grounds.

A summary in our own words. The full account, with all its detail, is in the original write-up: read it at A Turbo'd Green NB Project – MX5 Nutz ↗

Worth knowing

  • A stuck closed turbo actuator can cause dangerous over-boost that may be mistaken for normal performance
  • The Gen 1 ME221 ECU has a known idle droop firmware limitation that cannot be fully fixed, only remapped around
  • Cheap rust repair quotes vary hugely, so it can be worth patching and covering arches short term rather than paying full repair cost immediately

A Turbo'd Green NB Project – MX5 Nutz

forum thread: 1 of 1 pages and 37 of 42 posts inspected; 19 unquoted updates by ShawLovelock used; 18 replies excluded; coverage is partial on 3 November 2026. The original write-up and photographs remain with their creators. This page is a catalogue in our own words, and a signpost to the source.

Read the full write-up at A Turbo'd Green NB Project – MX5 Nutz ↗

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