B58 Tuning Guide: Supra, M340i & Beyond

B58 Tuning Guide: Supra, M340i and Beyond

Platform: A90/A91 Supra | M340i | M440i | M240i | 340i | 440i | 540i | X3 M40i

The B58: BMW's Most Versatile Modern Engine

The B58 is a 3.0-liter single-turbocharged inline-six that BMW has put in just about everything — from the A90 Supra to the M340i, M440i, M240i, and even the X3 M40i. It is not the motorsport-derived S-series engines, but do not let that fool you. The B58 is an incredibly capable tuning platform that responds well to modifications and has a robust bottom end that handles serious power.

Stock output varies slightly by application, but expect roughly 340-380 whp at the wheels across the lineup.

Gen 1 vs. Gen 2 B58

There are two versions of the B58, and they matter:

• Gen 1 (B58B30M1): Found in the 2020 A90 Supra and earlier 340i/440i/540i models. Open-deck block design, slightly different exhaust manifold integration.
• Gen 2 (B58B30O1): Found in the 2021+ A91 Supra, M340i, M440i, and M240i. Closed-deck block, integrated exhaust manifold in the cylinder head, and slightly revised turbo.

Both generations tune similarly and make comparable power at most stages. The Gen 2's closed-deck design gives it a slight edge in durability at extreme power levels, but for the vast majority of builds — tune through FBO — the difference is academic. Stock power output between the two is nearly identical.

Power Stages

Downpipe + Tune: The Best Bang for Your Buck

A downpipe and tune is one of the best bang-for-buck upgrades in the entire BMW world. On the B58, the factory downpipe is extremely restrictive — it houses the primary catalytic converter right at the turbo outlet, choking exhaust flow significantly. Replacing it with a high-flow downpipe (catted or catless) and pairing it with an ECU tune picks up 60-90 whp over stock on 93 octane alone.

For many B58 owners — especially M340i and Supra daily drivers — a downpipe and tune is the entire mod list. It transforms the car from "quick" to "fast" without any compromise to drivability, reliability, or daily-driver comfort. The car still starts perfectly, idles smoothly, and passes through traffic without attracting attention. But when you get on it, the difference is unmistakable.

Ethanol: Not Optional, Game-Changing

Adding ethanol to a tuned B58 is a major step forward in power. E30 on top of a full bolt-on setup is a big, noticeable jump — the kind of improvement you feel in your seat without needing to look at a dyno sheet. The higher octane rating of ethanol lets the tuner advance timing and increase boost without risking detonation.

A flex fuel sensor is required for running any ethanol blend. This is not optional. The sensor mounts in the fuel line and reads the actual ethanol content in real time, sending that data to the ECU so the tune can adjust fueling and timing on the fly. Without it, the ECU has no way to know what is in the tank. Running ethanol without a flex fuel sensor is a recipe for a lean condition and potential engine damage.

Most B58 owners who run ethanol use an E30 blend — roughly 30% ethanol, 70% pump gas. It is easy to mix at the pump, does not significantly increase fuel consumption, and works fine in cold weather. E50 and E70+ push more power but come with higher fuel consumption and potential cold-start challenges in winter climates.

Stock Turbo Ceiling

The factory B58 turbocharger tops out at approximately 530-560 whp. You can push it to the upper end of that range on aggressive E70+ tuning with full bolt-ons, but beyond that the turbo is out of airflow. It is done. No amount of additional tuning will extract more — the compressor wheel is the bottleneck.

This is actually a generous ceiling for a stock turbo. Many B58 owners live happily in the 450-530 whp range for years without needing more. But if you want to go further, a turbo upgrade is the only path.

Turbo Upgrades: Pure800 and KLM SAVAGE

When the stock turbo runs out of breath, the two most popular upgrade paths are:

• Pure800: A drop-in turbo upgrade that uses the factory turbo location and mounting. Targets 550-700+ whp depending on fuel and supporting mods. Excellent spool characteristics for a street car — the power delivery is linear and predictable.
• KLM SAVAGE: A more aggressive turbo option targeting 700-1000+ whp. This is the choice for dedicated track cars or high-power street builds. Requires more supporting modifications — upgraded fuel system, intercooler, and potentially built internals at the top of the power range.

Both options are well-proven in the B58 community with extensive tuner support.

Platform-Specific Notes

A90/A91 Supra: The Supra uses the B58 with a ZF 8-speed auto (A90) or a manual gearbox option (A91 2023+). The ZF trans handles B58 power levels well through the FBO range. The Supra is the lightest B58 platform at roughly 3,400 lbs, so it feels the most dramatic at any given power level.

M340i / M440i: Slightly heavier than the Supra at 3,800-3,900 lbs with AWD. The xDrive system provides excellent traction for putting power down. A tuned M340i is a legitimate fast car that nobody sees coming.

M240i: The newest and smallest B58 platform. Similar weight to the Supra, available in both RWD and xDrive. An absolute sleeper — most people do not even know what it is, and a tuned one will walk cars that cost twice as much.

The Build Path That Makes Sense

1. Downpipe + ECU tune. Start here. The single best modification you can do on a B58, period. Immediate, dramatic improvement.
2. Intake + charge pipe. Feeds the turbo better air and replaces the failure-prone factory plastic charge pipe.
3. Front-mount intercooler. Keeps intake temps consistent, especially in warm weather or during spirited driving.
4. Flex fuel sensor + E30. Unlocks the ethanol advantage without going extreme. Big power gain for low cost.
5. Turbo upgrade (Pure800 / KLM SAVAGE). When 530-560 whp is not enough and you want to play in the 700+ whp range.

Start Your Build

Ready to tune your B58? Check out our packages page to explore pre-built packages and parts for your platform.