ND MX-5 Forced Induction: Supercharger vs Turbo at 7 psi

A complete bolt-on supercharger or turbo kit for the ND 2.0 lands roughly $5,000–$6,700 in hardware and makes around 225–250 hp at the crank on stock internals. The hard limit is the connecting rods: BBR, who builds kits for this engine, calls the SkyActiv 2.0 rods “the weakest connecting rods we have seen,” and every in-house failure they logged happened at 10 psi or higher even with correct fueling and no knock (BBR). That is why every reputable kit caps Stage 1 around 7 psi. Past that you are rebuilding the bottom end.

Supercharger or turbo: pick by how you drive

Both make similar power on stock internals. The split is character, install complexity, and what else they stress.

	Supercharger (Rotrex / Eaton)	Turbo (BBR / Garrett)	Verdict
Power delivery	Instant, linear, builds with rpm	Bigger midrange, more peak, some lag	SC for street feel, turbo for the dyno number
Stock-internals power	~225–250 hp crank	~248 hp crank @ 7 psi	Effectively tied at the safe limit
Install	Simpler, fewer stock parts touched	More plumbing, downpipe, manifold	SC is the easier weekend
Parts count / reliability	Fewer parts, slight edge	More heat, more drivetrain stress	SC, marginally (Reddit)
CARB-legal path	Edelbrock E-Force, ND1 2.0	BBR via Flyin’ Miata, ND1 only	SC if you live in California

Owners debating the two give the supercharger “the slight edge on reliability… because it has less parts involved,” while the turbo trades that for more area under the curve (r/Miata). The stock-internals ceiling is so close that the decision is rarely about the peak number.

What the ND engine you have starts at

Forced-induction math depends on which engine is under the hood.

• ND1 2.0 (2016–2018): 155 hp, 148 lb-ft at the crank (Motor1).
• ND2 2.0 (2019+): ~181 hp, higher redline, revised, reinforced internals. See ND1 vs ND2 vs ND3 for what changed.
• 1.5 SkyActiv-G: never sold in the US. If you have one, you are in Europe, Japan, or Australia.

The ND2’s reinforced internals matter here. Owners running boost prefer the ND2 short block precisely because “it has had more reinforcement done to it,” and cite reliable 250-hp ND2 builds (r/Miata). The rod weakness BBR describes applies to the SkyActiv 2.0 broadly, but the ND2’s added reinforcement makes it the safer starting point at the top of the stock-internals band.

Realistic power, and why the big whp claims run hot

Vendor crank figures from the kit makers themselves:

• Turbo (BBR Stage 1): 248 bhp at 7,150 rpm, 236 lb-ft at 3,250 rpm, with over 200 lb-ft from 2,750–6,500 rpm, on a “conservative” 7 psi (BBR). That is 0–60 in 5.0s against a ~7.3s stock car.
• Supercharger (BBR Rotrex): Stage 1 225 hp / 200 lb-ft, Stage 2 245–250 hp / 216 lb-ft (Motor1).
• Turbo, 1.5: ~210 hp / 197 lb-ft at 7 psi, a gain of +81 hp and +86 lb-ft over stock (tiremeetsroad).

You will see higher numbers quoted: 250–280 wheel hp for superchargers, 280–300 wheel hp for an HKS turbo (Worth Driving). Treat those as best-case ceilings. They run well above the kit makers’ own crank dynos, and wheel figures past the safe boost limit imply built internals, E85, or both. The realistic stock-internals band is roughly 225–250 hp at the crank, about 200–225 at the wheels.

The rods bend at 10 psi, so 7 psi is the wall

This is the one fact that governs every ND forced-induction build. BBR’s testing is blunt: stock rods bend at 10 psi or higher, and “all in-house failures have been experienced at 10psi or higher” even with a correct air-fuel ratio and no detected knock (BBR). The failure is mechanical, not a tuning mistake you can dial out. Practical safe ceiling: below ~230 lb-ft and ~7 psi.

The high 13.1:1 compression ratio is not the disqualifier people assume. Direct injection, the piston geometry, and aggressive closed-loop knock control let the engine tolerate mild boost, comparable in spirit to the S2000’s 11.7:1 or the BRZ’s 12.5:1 running boost (TurboSource). One test car ran +70 rwhp / +100 rwtq over stock for ~3,000 hard miles including track without failure (TurboSource). But high compression shrinks the knock margin, so fuel quality, intake air temps, and tuning matter more here than on a low-compression engine.

Two other stock parts give out near the same point:

• The clutch. BBR capped Stage 1 partly because “the standard clutch will not take more torque than our stage one conversion” (BBR). Above Stage 1 you need an upgraded clutch and flywheel.
• The transmission. Cup-racing ND transmissions failed at near-stock power, and owners report ND1 gearboxes snapping both stock and boosted (TurboSource). Higher-power turbo builds commonly swap to an NC transmission with an NC or Spyder differential and a Flyin’ Miata adapter plate (r/Miata).

Past ~7 psi the build changes category. Forged rods plus low-compression forged pistons unlock “280BHP+” safely (BBR), but that is an engine-out rebuild, not a bolt-on.

What you have to buy besides the blower

A kit is not just the supercharger or turbo. Required supporting mods, build-dependent:

• ECU tune. Non-negotiable. EcuTek RaceRom is the standard platform the BBR and Flyin’ Miata kits are built around (EcuTek). See ECU tune for how flashing works on the ND.
• Charge cooling. A front-mount intercooler on turbo kits, a charge cooler on superchargers. Both BBR turbo kits ship one (BBR).
• Fueling. Sub-250 hp builds can run the stock pump with larger injectors; higher-power turbo builds need a high-flow pump, lines, and injectors (Worth Driving). One owner documents the injector-plus-pump install for a JDL turbo kit (r/Miata).
• Exhaust and downpipe. A stainless downpipe and high-flow exhaust come with the turbo kit; superchargers benefit from a freer exhaust at Stage 2.
• Cooling and oil. An oil cooler and upgraded cooling are standard recommendations on a boosted, tracked car (Worth Driving).
• Drivetrain, above Stage 1. Clutch, flywheel, and often the NC transmission and differential swap noted above.

Rough cost: budget past the sticker

Complete kits, hardware only:

• BBR 2.0 turbo: £4,395 DIY to £4,995 fitted, ex-VAT (~$5,800+) (BBR).
• BBR Rotrex supercharger: £3,895 parts to £5,990 with Stage 2 software (Motor1).
• Edelbrock E-Force supercharger: $6,650.95, fits under the stock hood with a self-contained oil system rated for a 100,000-mile service interval (MiataSpeed).

That is the part number on the box. Real all-in cost is higher: overseas buyers report $11,000–$12,000 once import and install are added, and one owner called $11–12k “very steep for 50 more Hp” over a tune (r/Miata). Built internals, a clutch, and a transmission swap add thousands more on top if you exceed Stage 1. Resale works against you too: a boosted ND reads to buyers as a “project car,” which lowers what it brings (r/Miata).

Warranty and CARB: read this before you buy

Forced induction will almost certainly void your powertrain warranty. Owners report dealers scrutinizing even a muffler swap, with one 2020 ND going into limp mode and the dealer immediately asking about the aftermarket exhaust (r/Miata). The blunt community read: adding significant power via a supercharger is reasonable grounds to deny a transmission claim, and contesting a denial means hiring a lawyer against corporate Mazda. The CARB-legal Edelbrock kit mitigates this: it is listed with its own 3-year / 36,000-mile powertrain warranty per the vendor (Good-Win Racing).

For California, the legal path is narrow. The Edelbrock E-Force is sold as “50 State CARB Legal” for 2016+ ND 2.0L cars (MiataSpeed). The vendor listing attributes that exemption to P/Ns 1554 and 15540 covering 2016–2018 2.0L cars, paired with an emissions-legal EcuTek tune (Good-Win Racing). The CARB-legal turbo path, a 50-state BBR Stage 1 distributed by Flyin’ Miata, is ND1-specific (Flyin’ Miata). For a 2019+ ND2 in California, a supercharger is effectively your only emissions-legal option. Non-CARB builds fail smog and can trip cat-efficiency codes: one supercharged, tracked ND threw a P0421 and needed a new catalytic converter and an engine drop to fix it (r/Miata).

Verdict: same 225-250 hp window, pick by feel and CARB

If you want a faster ND on stock internals, both paths land in the same 225–250 hp crank window for similar money, and 7 psi is the wall either way. Pick the supercharger for linear street feel, the simpler install, and the only CARB-legal route on an ND2. Pick the turbo for the bigger midrange and the higher numbers if you are tuning past stock internals anyway. If your goal is just a livelier naturally aspirated car, an ECU tune and bolt-ons get most of the street-feel improvement for a fraction of the cost and none of the warranty or transmission risk.

Related pages

• ND ECU reflash / tune: the tuning step every boosted build needs
• ND1 vs ND2 vs ND3: which short block you are starting from
• First mods: where forced induction sits in the mod path
• Exhaust: supporting hardware for a boosted ND