niterydr's 1990 Miata NA VVT build

niterydr · 1990 Mazda Miata

Mazda MX-5 (Miata)

It's probably time for an introduction and build thread

Read the full write-up at It's probably time for an introduction and build thread ↗

Photo: It's probably time for an introduction and build thread

A 1990 Mazda Miata going from spec-legal autocrosser to a tinkerer's HPDE/time-trial project

Owner niterydr bought a "near spec ready" NA Miata, finished making it Spec Miata legal, then decided to abandon that class to build a more powerful track and time-trial car instead. The thread covers suspension, brake and wiring upgrades, a speed-density ECU conversion, and the start of a VVT 1.8 engine rebuild and aero package.

Specs

As stated in the original write-up.

Rear differential: 4.3 Torsen in an RX-7 housing
Suspension bushings: Energy Suspension bushings throughout
Rear shock mounts: Goodwin Racing extended rear travel rear shock mounts
Bump stops: 36mm bump stops added (car had none)
Shocks: B8 NB shocks
Springs: 700/325 lb spec springs retained
Sway bars: Spec Miata sway bars
Brakes: Gloc pads, 1.8 caliper upgrade, stainless steel lines, Motul 600 fluid, proportioning valve added
Brake ducts: Singular Motorsports brake ducts
Lighting: Popup headlights deleted, projector lights in turn signal housings
Hood vents: Singular Motorsports hood vents
ECU: Megasquirt MS3 with flex fuel, speed density conversion
Injectors: NB2 flowed injectors
Intake: DIY intake routed through fender area
Dash: PI dash planned
Weight: 2,341 lbs with driver and full tank of fuel
Wheels/Tyres (at time of testing): 15x7 wheels with 225 RS4 tyres, 15x9 wheels planned
Engine (spare, in progress): 1990 1.6 engine currently fitted; separate low-mileage 1.8 VVT engine being rebuilt with Wiseco pistons, decked block, polished and magnafluxed crank, RB header

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 3

DIY intake
Fabricated intake routed through the fender area as part of speed density conversion
Wiseco pistonsWiseco
Block set up, decked and boiled for new pistons during VVT engine rebuild
In the shops
Wiseco Seamless Piston Ring Installer ↗Flyin' Miata· $37.99 USD
Wiseco Piston Ring Set ↗Flyin' Miata· $33.99 USD
Forged Turbo Pistons by Wiseco (1.8L NA/NB) ↗Flyin' Miata· $1,099.00 USD
RB headerRB
Acquired along with mounts for the spare VVT engine swap

Fuel & Ignition 2

Megasquirt MS3 ECUMegasquirt
Installed with flex fuel capability for full tuning control and logging
Flowed fuel injectors
NB2 injectors reused in the speed density conversion

Gearbox & Drivetrain 1

4.3 Torsen differential in RX-7 housing
Swapped in as a deal, fitted to the rear end
In the shops
Differential Housing Breather / Vent ↗MazSpec MX-5 Spares & Accessories· £10.83 GBP
Torsen Limited Slip Differential - Mk1 ↗MX5 City· $569.45 USD
Torsen Limited Slip Differential - Mazda MX5 (94-05) ↗Timms24 Classic Ford Parts – Capri Mk1 catalogue· €624.90 EUR

Suspension & Steering 6

Energy Suspension bushingsEnergy Suspension
Replaced worn bushings in all suspension bushing locations
In the shops
Energy Suspension Hyper-Flex Master Bushing Set ↗Moss Miata· $395.00 USD
Polyurethane Sway Bar Bushing Set (Energy Suspension) ↗Moss Miata· $22.99 USD
Energy Suspension Polyurethane Rear Control Arm Bushings ↗Moss Miata· $148.00 USD
Extended rear travel rear shock mountsGoodwin Racing
Fitted while suspension was apart to allow more rear travel
In the shops
Bump Stop Spacers for Fox Shocks ↗Flyin' Miata· $1.49 USD
BLOX Racing Roll Center Adjusters and Extended Front Ball Joints (06-11 Civic) ↗JDMuscle — Mazda MX-5· $152.10 USD
BC Racing Coilovers for Deepal SL03/L07 Extended Range C385 RWD (2021-Present) ↗Paramount Performance· $0.00 USD
36mm bump stops
Added since the car had none fitted previously
In the shops
Improved Bump Stops (Pair) ↗Flyin' Miata· $29.99 USD
Koni STR.T Shock and Bump Stop Set, 1990-97 ↗Flyin' Miata· $549.00 USD
Koni STR.T Shock and Bump Stop Set, 2006-15 ↗Flyin' Miata· $669.00 USD
Torrington thrust bearings
Installed while suspension components were disassembled
In the shops
Mazda Thrust Bearing (2001-05 Engine) ↗Flyin' Miata· $65.99 USD
Performance Thrust Washer/Bearing Set ↗MazSpec MX-5 Spares & Accessories· £5.99 GBP
ACL Race Thrust Bearing (1990-00 Engine) ↗Flyin' Miata· $10.79 USD
B8 NB shocks
Used as interim shock solution
Spec Miata sway bars
Retained front and rear sway bars from Spec setup
In the shops
Flyin' Miata Rear Sway Bar (ND Chassis) ↗Flyin' Miata· $169.00 USD
Flyin' Miata Front Sway Bar (NB Chassis) ↗Flyin' Miata· $219.00 USD
Flyin' Miata Front Sway Bar (NA8 Chassis) ↗Flyin' Miata· $219.00 USD

Brakes 6

Brake padsGloc
Fitted for improved stopping power
1.8 brake calipers
Upgraded from 1.6 calipers for better braking
Stainless steel brake lines
Retained from prior setup
In the shops
Extended Stainless Steel Clutch Lines by Cobalt ↗Moss Miata· $19.99 USD
Stainless Steel Brake Line Kit ↗Moss Motors – Triumph TR6/TR250· $431.50 USD
Stainless Steel Braided Brake Lines ↗Moss Motors – Triumph TR6/TR250· $115.75 USD
Brake fluidMotul 600
Used for improved high-temperature performance
In the shops
Motul Transmission Fluid 80W90 (1L) ↗Moss Miata· $15.99 USD
Proportioning valve
Added to balance front/rear brake bias
Brake ductsSingular Motorsports
Added for cooling while working on the brakes

Body & Trim 2

Projector headlight conversion
Popup headlights deleted and projectors mounted through turn signal housings to stay legal for some event classes
In the shops
Spec-D Halo Projector Headlights (Miata 2001-2005, Black) ↗Roadster360· $255.00 USD
ANZO Projector Headlight Set with Halo (06-11 Civic) ↗JDMuscle — Mazda MX-5· $435.00 USD
Black Classic HID Projector Headlight Kit (84-86 300ZX) ↗Motorsport Auto (The Z Store)· $479.87 USD
Hood ventsSingular Motorsports
Added for cooling/aero
In the shops
Locking Clip for Hood Lift Kits ↗Flyin' Miata· $1.49 USD

Photos

59 pictures collected from the write-up, in the order they were posted, shown from It's probably time for an introduction and build thread. A picture opens larger here, with the way through to the page it is on.

It's probably time for an introduction and build thread - Miata Turbo Forum - Boost cars, acquire cats. 39this post at It's probably time for an introduction and build thread ↗

Picking up the Miata in CressonPhoto: It's probably time for an introduction and build thread

Original interior condition after purchasePhoto: It's probably time for an introduction and build thread

Car in the garage after bringing it homePhoto: It's probably time for an introduction and build thread

Car home from a track day in stock specPhoto: It's probably time for an introduction and build thread

Hood vents fitted to the carPhoto: It's probably time for an introduction and build thread

DIY intake built for speed density setupPhoto: It's probably time for an introduction and build thread

Megasquirt MS3 wiring preparationPhoto: It's probably time for an introduction and build thread

Leave a poscatPhoto: It's probably time for an introduction and build thread

Leave a negcatPhoto: It's probably time for an introduction and build thread

It's probably time for an introduction and build thread - Miata Turbo Forum - Boost cars, acquire cats. 16this post at It's probably time for an introduction and build thread ↗

Suspension work during alignment sessionPhoto: It's probably time for an introduction and build thread

Brake duct clearance checkPhoto: It's probably time for an introduction and build thread

Getting quickerPhoto: It's probably time for an introduction and build thread

Goal on session 4 was try to run as consistent as possible. Laps 1 and 4 had point bysPhoto: It's probably time for an introduction and build thread

Its shiny. Im going to wrap it bronze to match my future wheels.Photo: It's probably time for an introduction and build thread

Tweet this threadPhoto: It's probably time for an introduction and build thread

It's probably time for an introduction and build thread - Miata Turbo Forum - Boost cars, acquire cats. 4this post at It's probably time for an introduction and build thread ↗

Block in the left bin. Setup for Weisco pistons, decked, boiled. Crank magna fluxed and polished in right bin.Photo: It's probably time for an introduction and build thread

Nine lives ****Photo: It's probably time for an introduction and build thread

Almost done with the splitter. Need to build ducting next.Photo: It's probably time for an introduction and build thread

Need to build some ducts.Photo: It's probably time for an introduction and build thread

How it was done

Starting condition and purchase

The car came from Cresson Motorsports Ranch as a "near spec ready" 1990 Miata. The owner spent much of the prior year finishing the Spec Miata legal conversion, adding required HVAC and safety gear, and got it track-day legal by August.

Reassessment after a track day

At Eagle Canyon Raceway the car leaked fuel from the cap in left-handers and the left rear suspension bottomed out. Inspection revealed worn-out rear upright bushings. The owner decided Spec Miata rules were not for him and switched goals toward HPDE and time trial under NASA and gridlife rules.

Suspension and brakes

Fitted a 4.3 Torsen differential in an RX-7 housing, Energy Suspension bushings throughout, Goodwin Racing extended rear shock mounts, new bump stops, and Torrington thrust bearings while the suspension was apart. Kept 700/325 springs and Spec sway bars for now. Upgraded brakes with Gloc pads, 1.8 calipers, Motul 600 fluid, a proportioning valve and brake ducts, though a caliper o-ring leak surfaced during bedding and stopped a planned autocross.

Electronics and fuelling

Converted the 1.6 engine to speed density with a DIY fender-mounted intake, installed a Megasquirt MS3 ECU with flex fuel capability, reused flowed NB2 injectors, and planned a PI dash. Early testing included setting camber, toe and caster and weighing the car, followed by base tune work and a faulty coolant fan relay repair.

Engine rebuild and aero

A low-mileage 1.8 VVT engine on a stand showed poor leakdown, so the owner acquired a second VVT head and later had the block decked, set up for Wiseco pistons, and the crank magnafluxed and polished, with the machine work finished by November. Separately, aero parts including a splitter and ducting were being fabricated for the still-running 1.6-powered car.

A summary in our own words. The full account, with all its detail, is in the original write-up: read it at It's probably time for an introduction and build thread ↗

Worth knowing

Should have researched the purchase and other wheel-to-wheel options more before committing to Spec Miata legality work
A worn caliper o-ring can cause sudden brake failure, worth checking carefully after any teardown
Depowered steering feels very light and needs getting used to on rough roads