The Mazda MX-5 Miata (NA/NB, BP 1.8) is rated 142 hp (SAE net (142 hp, 2004 Miata) · US market) at 7,000 rpm and weighs 2,447 lb (US curb, 5MT (6MT 2,440 lb; automatic 2,473 lb)), or 17.2 lb/hp. On enthusiast estimates its stock internals are taken to about ~280 hp, the fuel system to around ~190 hp, and its naturally aspirated setup is taken to about ~155 hp before forced induction. Below: the sourced spec sheet, the limit sheet carbuildcheck analyzes against, and the platform's community-documented weak points.
Units
01 Spec sheet sourced
EngineBP · 1,839 cc · I4
Engine codeBP (1.8 DOHC VVT)
Bore × stroke83 × 85 mm
Compression10:1
Inductionnaturally aspirated
Fuel systemport
Rated power142 hp · SAE net (142 hp, 2004 Miata) · US market @ 7,000 rpm
GenerationNB2 (2001–2005, the sourced car: 142 hp); NB1 1999–2000 and NA 1.8 (1994–1997, 128–133 hp) and NA 1.6 (116 hp) share the chassis · 2001–2005 (NB2); NA 1989–1997; NB 1999–2005 · facelift (facelift / MC, Mazda’s term)
rotating assembly ceiling · fails first: pistons and head gasket past ~8 psi · 91 AKI · no named source: site planning estimate · site planning figure ~280 hp; the community recipe of 6–8 psi on stock internals was not found on a fetched page
Induction ceiling~155 hp
naturally aspirated ceiling (bolt-ons and cam) · fails first: NA ceiling: header, intake, cams · 91 AKI · no named source: site planning estimate · site planning figure ~155 hp
Fuel system~190 hp
stock fuel-system ceiling · fails first: stock injectors on boost · 91 AKI · no named source: site planning estimate · site planning figure; no named source in this audit
Clutch (manual)~180 hp
stock clutch torque capacity · fails first: stock clutch slip · no named source: site planning estimate · site planning figure; no named source in this audit
Transmission (automatic)~220 hp
gearbox / driveline rating · fails first: gearbox at torque · no named source: site planning estimate · site planning figure; no named source in this audit
Cooling (sustained)~240 hp
thermal ceiling for sustained load · fails first: radiator capacity on track · no named source: site planning estimate · site planning figure; no named source in this audit
Tuning limitsenthusiast estimates, crank hp on the stated fuel; sources: none named yet; method: the analyzer plans on the lower bound of each range
⚑The community recipe holds: 6 to 8 psi on stock internals with a proper tune. Greed is what kills these engines.
⚑Check sills and frame rails for rust before spending a dollar. The chassis is the platform.
04 The typical path
Intake → headers → tune → cams or forced induction. NA gains are modest on most platforms; the big unlock is boost, and boost starts at the fuel system.
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