Rascal's 1999 Miata NB1 Track Spec Build
NB1 Track spec build - stock thru to C30-84'd
Read the full write-up at NB1 Track spec build - stock thru to C30-84'd ↗
Photo: NB1 Track spec build - stock thru to C30-84'dA 1999 NB1 Miata track car built from stock to a C30-84 supercharged setup
Owner rascal has run this 1999 NB1 Miata as a dedicated time-attack track car since 2009, progressing from stock suspension and bolt-on power mods through naturally aspirated head work and ITBs, before settling on a Rotrex C30-84 supercharger kit to hit a class power limit of 185hp. The thread documents over a decade of reliability lessons, dyno chasing, and mounting failures and fixes.
Specs
As stated in the original write-up.
- Induction
- Rotrex C30-84 supercharger with TDR mounting kit, Cooling Pro intercooler, standard NB1 inlet manifold
- ECU
- Adaptronic E420c
- Ignition
- COP system using Toyota coils from a 2000 Corolla
- Cooling
- 42mm alloy radiator, relocated engine oil cooler and Rotrex oil cooler in front fenders
- Suspension
- TEIN coilovers, local sway bars, poly bushes, offset front lowers for camber (later refreshed with new coilovers, 863 bronze bushing kit, new ELBJs)
- Brakes
- New rotors, Hawk Blue pads, hi-temp brake fluid
- Tyres
- R888s
- Wheels
- Kosei 15x7 +17 (later 8 inch rims fitted)
- Roll cage
- Welded in half cage with race seat and harness
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
- Ported head with bigger valves and heavier springs
Head work intended to raise power, later found not to flow as expected
- TrackDog Racing Rotrex mounting kit
Replaced failure-prone local mounting kit after belt shredding and pulley failure
- Supertech pistons and Manley rods
Used in the rebuilt bottom end for the supercharged setup
In the shops
MANLEY H BEAM RODS ↗
MiataSpeed· $457.20 USDManley Performance Piston Ring Set (95.5mm Bore) ↗
JDMuscle — Mazda MX-5· $66.61 USD
Manley 99.50mm STD Bore Piston (04-14 WRX/STI EH257) ↗JDMuscle — Mazda MX-5· $202.15 USD
Fuel & Ignition 3
- Adaptronic E420c ECU
Controls fuelling and tuning for bolt-ons and later forced induction
- Toyota Corolla coil-on-plug coils (2000 Corolla)
Replaced failing factory coil packs with a custom COP conversion
In the shops
Toyota Corolla Panasport Z-Light Wheels ↗
Sports & Classics· $0.00 USD
Toyota Corolla AE86 4AGE Oil In Assembly ↗
C Bradley Motorsport· £91.90 GBP
Starter Motor for Toyota Corolla AE86 4AGE ↗C Bradley Motorsport· £193.90 GBP - Techno ToyTuning manifold with AE86 Silvertop throttle bodies
Installed as an individual throttle body setup, later removed
In the shops
Throttle Body Seal to Inlet Manifold | Genuine Land Rover LR040241 ↗
Moss Motors – Triumph TR6/TR250· $13.25 USD
Cooling 2
- 42mm alloy radiator
Replaced failing factory radiator to cope with added power
In the shops
Alloy Radiator by Ron Davis ↗Moss Motors – Triumph TR6/TR250· $2,261.25 USD
Alloy Radiator by Ron Davis ↗Moss Motors – Triumph TR6/TR250· $2,418.55 USDAlloy Radiator (Pre-1990 Mini) ↗
bpnorthwest.com· $725.00 USD - Cooling Pro intercooler
11x12x3 inch intercooler fitted ahead of the radiator for the supercharger setup
Gearbox & Drivetrain 1
- Forged rods and high compression pistons
Built into a new bottom end for a bulletproof rebuild
In the shops
Forged Turbo Pistons by Wiseco (1.8L NA/NB) ↗
Flyin' Miata· $1,099.00 USD
Forged Turbo Pistons by Wiseco (1.6L NA/NB) ↗Flyin' Miata· $869.00 USD
Piston Set, 020 (Jaguar 4.2 High Compression) ↗bpnorthwest.com· $679.59 USD
Suspension & Steering 5
- TEIN coilovers
Fitted as first suspension upgrade for track use
In the shops
Coilover, flex-z, Tein ↗Moss Europe (UK)· £1,608.00 GBP
Coilover, flex-z, Tein ↗Moss Europe (UK)· £1,703.75 GBP
Coilover, flex-z, Tein ↗Moss Europe (UK)· £1,421.00 GBP - Poly bushes (all round)
Replaced factory bushings for sharper handling
In the shops
Tie Bar Kit with Poly Bushes and Hardware ↗bpnorthwest.com· $99.94 USD
Rear Radius Arm Bushes Pair, Poly (To Body, Driveshaft Models) ↗James Paddock Ltd· £32.50 GBP
Exhaust Mounting Poly Bushes (Rear Subframe Arm) - Set of 8 Pairs ↗ - Offset front lower control arms
Added for extra front camber
In the shops
Front Control Arm Lower-Inner Rear Bushing Kit - Double Offset ↗
Moss Miata· $86.99 USD
Front Upper Control Arm Inner Bushing Kit - Camber Adjustable Double Offset ↗Moss Miata· $79.99 USD - Goodwin Racing heavy duty sway bar mounts
Fitted, later complicating radiator mount relocation
In the shops
Heavy Duty Sway Bar Mounts (NA/NB) ↗Flyin' Miata· $189.00 USD
Heavy Duty Sway Bar Link Set (Sprite/Midget) ↗bpnorthwest.com· $59.90 USD
ACT Heavy Duty Pressure Plate ↗MiataSpeed· $311.99 USD - 863 bronze bushing kit
Fitted during suspension refresh
In the shops
Bronze Shifter Bushing ↗Moss Miata· $39.99 USD
Upgraded Bronze Shifter Bushing (5X Racing) ↗Moss Miata· $0.00 USD
Bronze Bushing 1st/3rd Gear - Triumph TR ↗Betaset (France)· €61.18 EUR
Brakes 1
- Hawk Blue brake pads
Fitted with new rotors and fresh fluid before first track event
In the shops
Hawk DTC-60 Race Rear Brake Pads (Escort/Miata) ↗MiataSpeed· $178.99 USD
Hawk DTC-50 Race Front Brake Pads (94-05 Miata) ↗MiataSpeed· $174.99 USD
Hawk DTC-60 Rear Race Brake Pads (Escort GT/Miata) ↗MiataSpeed· $182.99 USD
Wheels & Tyres 2
- Kosei wheels, 15x7 +17
Fitted early in the build
- R888 tyres
Fitted for first track outing
Body & Trim 4
- Welded half cage
Installed for safety while keeping the car road registered
- 3D rear wing and spare boot lid
Fitted for class-legal aero after moving up a class
In the shops
Genuine Mazda Boot Lid Weatherstrip Seal (Soft Top) ↗
MazSpec MX-5 Spares & Accessories· £46.98 GBP
Genuine Mazda Boot Lid Rubber Weatherstrip/Seal - PRHT ↗MazSpec MX-5 Spares & Accessories· £77.99 GBP
Boot/Trunk Lid Harness ↗Moss Motors – Triumph TR6/TR250· $21.99 USD - Plywood undertray and front splitter
Fabricated and painted to smooth underbody airflow
- Hardtop
Fitted to smooth airflow onto the rear wing
Interior 1
- Race seat and harness
Installed for track safety alongside the cage
Photos
43 pictures collected from the write-up, in the order they were posted, shown from NB1 Track spec build - stock thru to C30-84'd. A picture opens larger here, with the way through to the page it is on.
rascal · Jan 3, 2021 | 04:12 AM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jan 3, 2021 | 04:34 AM 4this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jan 25, 2021 | 09:36 PM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jan 25, 2021 | 10:12 PM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jan 25, 2021 | 10:14 PM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jan 25, 2021 | 10:18 PM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 15, 2021 | 07:10 PM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 15, 2021 | 08:29 PM 3this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 16, 2021 | 01:28 AM 5this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 20, 2021 | 02:38 AM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 23, 2021 | 07:38 AM 2this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 27, 2021 | 10:39 PM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Feb 27, 2021 | 10:55 PM 2this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jun 11, 2021 | 03:18 AM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jun 12, 2021 | 02:14 AM 1this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jun 18, 2021 | 05:22 AM 4this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jun 21, 2021 | 04:46 AM 6this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jun 25, 2021 | 06:03 AM 2this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Jul 22, 2021 | 10:11 PM 2this post at NB1 Track spec build - stock thru to C30-84'd ↗
rascal · Mar 8, 2022 | 02:56 AM 3this post at NB1 Track spec build - stock thru to C30-84'd ↗
How it was done
Starting condition
Purchased in 2009 as a stock 1999 NB1 Miata with 61,000 miles, bought specifically to become a time-attack track car, replacing a lighter, more powerful nat-asp sprint car the owner had raced for years.
Safety and suspension
A welded half cage, race seat and harness went in first for safety, followed by TEIN coilovers, local sway bars, poly bushes and offset front lowers for extra camber, before any power work began.
Early power mods and first track outings
A cold air intake, headers, 2.5 inch exhaust and an Adaptronic E420c ECU were fitted and dyno tuned to stay under the class power cap. Brakes and tyres were freshened and the car debuted at Phillip Island, beating the club lap record despite a damp track.
Reliability fixes and chasing power
Repeated coil pack failures led to a Toyota coil-on-plug conversion. Later, a move up a class brought mild cams, adjustable cam gears, a rear wing, splitter and undertray, lifting power to about 151whp.
Head work, ITBs and setbacks
A ported head with bigger cams and valves unexpectedly lost power; after much tuning and a failed ITB conversion using AE86 Silvertop throttles on a Techno ToyTuning manifold, the car plateaued around 149hp before a full bottom-end rebuild with forged rods and high-compression pistons was needed when the old motor wore out, complicated by miswired cam gears.
Rotrex supercharger build
During a COVID pause, the owner researched forced induction and chose a Rotrex C30-84 centrifugal supercharger over a turbo or FFS blower, sourcing a DIY kit locally, a Cooling Pro intercooler and fabricating mounts, ducting and relocated oil coolers to fit it all in.
Further issues and current setup
The locally sourced Rotrex mounting kit proved weak, shredding belts and shearing the crank pulley at speed. Switching to TrackDog Racing's mounting kit solved this. The suspension was later refreshed with new coilovers and bushings, and the correct pulley size was fitted to reach the target 184.6hp.
A summary in our own words. The full account, with all its detail, is in the original write-up: read it at NB1 Track spec build - stock thru to C30-84'd ↗
Worth knowing
- Double-check that adjustable cam gear triggering nubs are correctly aligned, not just the timing marks themselves
- A cheap local supercharger mounting kit can cause belt shredding and pulley failure; a proven kit from an established supplier is worth the extra cost
- ITBs added little benefit on a forced induction setup since they must be enclosed in an airbox anyway
- Moving oil coolers and intercoolers into the fenders can free up space in front of the radiator without major bodywork