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slug_dub's Red NA Miata Build

slug_dub · Mazda MX-5 (NA)

Mazda MX-5 (Miata)

Red NA, and another red NA, and another red NA...

Read the full write-up at Red NA, and another red NA, and another red NA... ↗

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Forum log of an Australian owner's built NA Miata track car

slug_dub documents ongoing maintenance and small upgrades to his third red NA Miata, a car originally built by a friend (tbro) for Production Sports racing. The thread covers track-day fixes like diff seals and radiator mount noise, plus later work addressing oil temperature spikes, interior bracing, and idle issues. It also recounts the history of his two earlier red Miatas before this one.

Specs

As stated in the original write-up.

Differential
Torsen Type 2, 4.44 final drive
Intake
Cowl-fed intake, ITB-like character
Fuel
Runs E85

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 1

Cooling 1

  • Oil cooler

    Used unit given by a friend, fitted with custom AN10 lines, brackets, sandwich plate and spacer to fix oil temp spiking

Gearbox & Drivetrain 2

Body & Trim 2

Interior 2

Electrical 2

Other 1

Photos

71 pictures collected from the write-up, in the order they were posted, shown from Red NA, and another red NA, and another red NA.... A picture opens larger here, with the way through to the page it is on.

Red NA, and another red NA, and another red NA, and another... - Miata Turbo Forum - Boost cars, acquire cats. 39this post at Red NA, and another red NA, and another red NA... ↗

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Red NA, and another red NA, and another red NA, and another... - Miata Turbo Forum - Boost cars, acquire cats. 32this post at Red NA, and another red NA, and another red NA... ↗

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How it was done

The car's background

This is the owner's third red NA Miata. It was built by a friend, tbro, for Production Sports racing and acquired by slug_dub in November 2015. He does not claim credit for the original build and uses the car as his daily driver as well as for track days.

Earlier red Miatas

Before this car, the owner had a 1991 NA he modified and painted himself, finding he disliked painting. A road trip from Brisbane to Melbourne cemented his love of driving Miatas, leading his friend to later buy him an NA8 with air conditioning.

Routine track-day fixes

Ahead of a track day the owner replaced diff seals, serviced brakes and oil, and tracked down a squeak from a radiator mount bolted to the chassis with spot welds. He drilled it out, swapped in a stock radiator to gain clearance, and discussed options for heavy-duty radiator box mounts like AWR or Racing Beat kits without committing to one yet.

Oil cooler and wiring fix

After noticing spiking oil temperatures at the track in 2021, the owner fitted a used oil cooler given by a friend, making brackets, AN10 lines, a sandwich plate and spacer. While removing the exhaust manifold for coating and wrapping, he found the oil temp sensor wire had melted near the exhaust, likely the real cause of the false readings. He also fitted an inexpensive short shifter with an extension.

Interior bracing and vents

The owner fitted vented quarter windows and new door lining, made plastic covers for empty speaker holes, and installed FM rails and a butterfly brace that had been stored for years, after removing an old bashed cross bar. He noted a modest stiffness improvement from street driving.

Idle hunting issue

The owner diagnosed an idle hunting problem, initially suspecting the idle air control valve. A cheap aftermarket IACV from Aliexpress partly worked but grew erratic, so he refitted the original. A friend later found the coolant temperature sensor was intermittent, pointing to the likely cause.

A summary in our own words. The full account, with all its detail, is in the original write-up: read it at Red NA, and another red NA, and another red NA... ↗

Worth knowing

  • Spot-welded radiator box mounts need the radiator removed for drilling, so plan ahead before a track day
  • Running a wire near the exhaust can heat-damage it and cause false sensor readings
  • A cheap aftermarket IACV from Aliexpress did not reliably fix idle hunting

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