Rich's 1990 Eunos Roadster ("50 Shades of Silver") build

Rich · 1990 Eunos Roadster (NA MX5)

Mazda MX-5 (Miata)79-page write-up

50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum

Read the full write-up at 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum ↗

Photo: 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum

A 1990 Eunos Roadster being rebuilt with a drysump, multiplate clutch and swapped drivetrain

Zed. documents a long-running, still unfinished project on his 1990 Eunos Roadster, moving well beyond restoration into a heavily engineered build: throttle bodies, a drysump oiling system, a multiplate clutch, custom wiring, a relocated radiator and reworked brakes and diff. The thread is notable for its workshop-level detail on fabricating brackets, adapters and plumbing from scratch, though progress is intermittent and many ideas are tried, abandoned or left pending.

Specs

As stated in the original write-up.

Front brakes: Wilwood Forged Dynalite Internal (120-13839) calipers with Supermiata Boxmount brackets and 280mm ND Mx5 discs
Throttle bodies: Jenvey TBP45I 45mm throttle bodies on a Jenvey DCOE-pattern inlet manifold
Exhaust: Cobalt stainless exhaust system fitted by the previous owner, retained with new tailpipe

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

Pace 3-stage drysump oil pumpPace
Used to build a drysump oiling system for the engine

Fuel & Ignition 2

Jenvey TBP45I 45mm throttle bodiesJenvey
Fitted to the inlet manifold replacing smaller 42mm units for better bore/tuning match
In the shops
Jenvey Dynamics 45mm Twin Throttle Bodies ↗C Bradley Motorsport· £499.90 GBP
Jenvey Throttle Bodies 2L Pinto TBP45 Kit ↗C Bradley Motorsport· £780.00 GBP
Jenvey Double Linkage Kit for Throttle Bodies ↗C Bradley Motorsport· £189.80 GBP
Speeduino plug-and-play ECUDIY-EFI
Bought to learn Tunerstudio and run standalone engine management
In the shops
Haltech Elite 750 ECU with Plug'n'Play Harness (Mazda Miata 01-05) ↗MiataSpeed· $1,495.00 USD
Haltech Elite 750 ECU with Plug'n'Play Harness (Mazda Miata 90-95) ↗MiataSpeed· $1,495.00 USD
Haltech Elite 1500 ECU with Plug'n'Play Harness (Mazda Miata 01-05) ↗MiataSpeed· $1,793.00 USD

Cooling 1

VW Polo radiator
Fitted into a modified Mazda radiator frame for a more efficient crossflow cooling setup

Gearbox & Drivetrain 2

Quartermaster/Superclutch concentric release cylindersQuartermaster/Superclutch
Used for the multiplate clutch release system
In the shops
Factory Concentric Slave Cylinder Tube, 07-20 350Z-370Z ↗Motorsport Auto (The Z Store)· $88.87
JWT Upgraded Concentric Slave Cylinder (07-20 350Z-370Z) ↗Motorsport Auto (The Z Store)· $246.87
Factory Concentric Slave Cylinder Assembly, 07-20 350Z-370Z ↗Motorsport Auto (The Z Store)· $239.87
Kia Sportage front differential
Sourced to give a 4.78:1 final drive ratio for the project
In the shops
BC Racing Coilover Kit - Kia Sportage QL (2016-2022, AWD) ↗Paramount Performance· $1,068.17 USD
BC Racing Coilover Kit - Kia Sportage NQ5 (2023-Present, AWD/FWD) ↗Paramount Performance· $1,068.17 USD

Brakes 1

Wilwood Forged Dynalite Internal calipers (120-13839)Wilwood
Front brake calipers bought to replace earlier Dynalite design
In the shops
Wilwood Flexline Kit for Forged Dynalite Front Caliper - Black (90-99 Civic) ↗JDMuscle — Mazda MX-5· $79.94 USD
Wilwood Flexline Kit for Forged Dynalite Front Caliper (00-03 Civic Si, 94-01 Integra) ↗JDMuscle — Mazda MX-5· $78.11 USD
Wilwood Front Forged Dynalite Brake Kit - Red Calipers, Drilled Rotors (92-95 Civic, 93-97 Civic del Sol) ↗JDMuscle — Mazda MX-5· $1,043.20 USD

Wheels & Tyres 1

BBS wheels (from E30)
Fitted to the Eunos replacing the original TSW wheels

Interior 1

Taxi rear heater unit
Compact heater box sourced to free up footwell space for the oil tank

Other 1

Suzuki Cappuccino screenwash reservoirSuzuki
Fitted and mounted centrally in the engine bay as a replacement reservoir
In the shops
Screenwash Reservoir Cap ↗British Auto USA· $4.44 USD
BC Racing Coilovers - Suzuki Cappuccino EA11R/EA12R (1991-1998) ↗Paramount Performance· $1,068.17 USD

Photos

354 pictures collected from the write-up, in the order they were posted, shown from 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum. A picture opens larger here, with the way through to the page it is on.

Zed. · May 31, 2018 22:43:20 GMT 13this post at 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum ↗

Photo: 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum

Zed. · Jul 14, 2018 12:47:40 GMT 4this post at 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum ↗

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Zed. · Jan 8, 2021 22:36:56 GMT 5this post at 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum ↗

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Zed. · Mar 16, 2021 16:29:49 GMT 5this post at 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum ↗

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How it was done

Starting condition

Bought in January 2018, the Eunos had been imported in 2000 and had avoided salted roads early on, but had corroded sills, wheelarches and floors. The previous owner had replaced the clutch, cambelt and waterpump, fitted a mk2 dashboard conversion and a Cobalt stainless exhaust, and done some rust prevention. A cracked pedalbox with a dropped throttle pedal was found on inspection.

Dashboard, wiring and interior strip

Removing the dashboard to investigate the wiring conversion led to stripping seats and carpet, discovering a previously fitted rollcage with cut floors and parcel shelf, and ultimately repairing the original Eunos loom rather than using a donor mk1 dash loom.

Engine and exhaust tidying

The ISV was blanked, a temporary breather catchcan fitted, and a cracked thermostat housing skimmed on the lathe. The previous owner's decat and cobalt exhaust were removed, repaired where a cat sensor had broken, resealed with silicone, and refitted with a new tailpipe.

Drivetrain and clutch development

Zed. sourced a Kia Sportage front diff for a 4.78:1 final drive, a mk2.5 six-speed gearbox to be converted to a close-ratio five-speed, and worked extensively on a multiplate clutch using Quartermaster/Superclutch concentric release cylinders and a modified bellhousing.

Engine build and drysump

Work progressed on a longer-stroke/longrod engine combination using Honda pistons under consideration, a Pace three-stage drysump oil pump, a custom oil tank mounted in the passenger footwell, and comparison of cylinder heads including a 323 turbo B6t head and a Vauxhall XE head and crank.

Cooling, wiring and heater changes

A VW Polo radiator was fitted into a modified Mazda frame for a more efficient crossflow setup. The underbonnet loom was simplified for a standalone engine management system (a Speeduino ECU was acquired), with mil-spec bulkhead connectors, and a compact taxi-style heater box was sourced to clear space for the oil tank.

Progress so far

By the latest supplied updates the build remained incomplete, with ongoing experimentation on throttle body sizing, exhaust manifold fitment, brake caliper selection, subframe weight reduction and gearing, and the 1.6 Mazda engine reported replaced by a Vauxhall 2.0 XE unit, though full confirmation of the final specification is not available from the supplied posts.

A summary in our own words. The full account, with all its detail, is in the original write-up: read it at 50 Shades Of Silver / Projekt Oh God What have I bought now? | Mighty5s UK MX5 Forum ↗

Worth knowing

Silicone sealer works better than conventional exhaust paste or fire putty on slip joints and flanges
Bike throttle bodies from a Kawasaki ZX636 pair are mounted slightly too close together for a DCOE-pattern manifold
Wilwood's newer Dynalite caliper design lacks a thickness-adjusting spacer, removing one possible leak point