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MTK Archives · Mazda Roadster NA
Joy Fast Yellow Bird NA6C
EngineBP-ZE
Displacement1839 cc
Weight867 kg
Japanese tuning shop Joy Fast presents the Yellowbird NA8C, a dedicated time-attack Eunos Roadster engineered around lightweight precision and total chassis balance. Built to compete at the highest level of naturally aspirated circuit racing, the car prioritizes low weight, aerodynamic downforce, and predictable driver feedback to extract maximum cornering speed.
Car Gallery29 scans
Overview
| Chassis Code | NA8C |
|---|---|
| Drivetrain Layout | FR |
| Vehicle Weight | 867 kg |
| Concept | A purpose-built time attack machine focused on low weight, precise handling, and balance over brute force. |
Engine
| Engine Code | BP-ZE |
|---|---|
| Displacement | 1839 cc |
| Bore x Stroke | 86 x 85 mm |
| Compression Ratio | 11:1 |
| Pistons | high comp |
| Connecting Rods | Forged H-beam |
| Crankshaft | Lightened and balanced |
| Balancing / Assembly | Black Metal |
| Camshafts | TODA 288° |
| Cam Sprockets | TODA adjustable |
| Head Gasket | Metal, 0.8 mm |
| Cylinder Head | Ported and polished, modified combustion chambers, raised compression |
| Valvetrain | Oversized valves, uprated double valve springs, reinforced valve guides |
| Engine Mounts | MAZDASPEED |
| Throttle Bodies | FCR carbs |
Forced Induction
| Exhaust Manifold | Integral Kobe Master Spec EX, 45 to 60 mm |
|---|
Fuel & Ignition
| Fuel Pump | NISMO |
|---|---|
| Spark Plugs | NGK Racing grade 9 |
| Ignition | MSD ignition with ULTRA Blue Point leads |
Engine Management
| ECU | HKS F-CON V Pro 32-bit |
|---|---|
| Management Notes | Rev limiter and ignition timing mapped for throttle response |
Exhaust
| Exhaust / Muffler | full exhaust system |
|---|---|
| Piping | Full stainless, 60 mm main pipe, 80 mm tailpipe |
Cooling
| Radiator | Joy Fast aluminium, twin-layer, increased capacity |
|---|---|
| Oil Cooler | Earls 12-row |
| Oil System | Reinforced oil pump gear |
Drivetrain
| Clutch | Mechadoc OS Super Single, metal facing |
|---|---|
| Transmission | OS Giken cross-ratio gearset |
| Final Drive | 4.4 |
| Differential (Rear) | MAZDASPEED 2-way LSD |
Suspension
| Dampers / Coilovers | JIC |
|---|---|
| Spring Rate (Front) | 13 kg/mm |
| Spring Rate (Rear) | 11 kg/mm |
| Springs | Bestex |
| Sway Bars | Rod-end sway bar links |
| Suspension Notes | Optimized geometry |
Brakes
| Calipers | Maruha Motors 4-piston, front |
|---|---|
| Rotors (Front) | OEM NB |
| Pads | ENDLESS |
| Lines | Stainless braided |
| Balancer | Joy Fast |
Wheels & Tires
| Wheels | ENKEI ES Tarmac |
|---|---|
| Wheel Size (Front) | 15" 7.5J ET15 |
| Wheel Size (Rear) | 15" 7.5J ET15 |
| Tires | Yokohama Advan A048 |
| Tire Size (Front) | 205/50R15 |
| Tire Size (Rear) | 225/50R15 |
Chassis & Rigidity
| Roll Cage | Full |
|---|---|
| Reinforcement | Seam-welded door apertures and subframe, urethane reinforcement in places |
Exterior & Aero
| Front Bumper | Garage Vary |
|---|---|
| Side Steps | Garage Vary |
| Wing / Spoiler | Voltex GT wing |
| Bonnet / Hood | Garage Vary |
| Diffuser / Underbody | Large front splitter |
| Windows | Polycarbonate |
| Exterior Notes | FRP panels |
Interior
| Seats | Race bucket seats |
|---|---|
| Harness | SABELT 5-point |
| Steering Wheel | Personal |
| Interior Notes | Stripped interior, no AC, no sound deadening |
Performance
| Circuit | Tsukuba Circuit 2000 |
|---|---|
| Notable History | Roadster King Battle D Class competitor |
Other
| Thermostat | Billion |
|---|---|
| Damper adjustment | 40-way, Joy Fast and Parts Creator PCR Tsukuba spec |
| Top mounts | OEM NB |
| Suspension arms | Tubular, uniball-mounted, lengths optimized |
| Rear diffuser | Modified RE Amemiya |
| Hardtop | Lightweight, Oyama Auto |
| Canards | Front |
| Shift knob | Joy Fast |
| Status | Currently out of service |