B58 Racing

Buying guide · Gleb Blekher

BMW G20 M340i / G22 M440i Mods Guide: The Best B58 Upgrades, In Order

Short answer: Tune it first. On a G20 M340i or G22 M440i, a tune is the biggest gain for the money. Then add a downpipe and a Stage 2 map, an aluminum charge pipe, and better cooling. Fuel upgrades and ethanol come after that. Suspension, brakes and tires should keep pace with the power. Before you spend anything, check whether your car's DME can be flashed. Newer cars are the catch.

Parts and tunes in this guide are for off-road / competition use only. Not legal for use on public roads in the United States, including California.

I'm Gleb Blekher. I run B58 Racing out of Dallas, TX. My own B58 builds are an M240i (F22) and a 540i (G30), so most of my hands-on time is on the older cars. The G20 M340i, G22 M440i and G42 M240i share a lot of parts with each other, and the mod order is the same idea. This is the order I'd tell a G20 or G22 owner to follow.

First: what engine and DME do you have?

The 2020–2024 M340i, the M440i and the G42 M240i use the Gen 2 B58 (B58TU). The high-output version in these cars is coded B58B30O1. Gen 2 uses different charge pipes, fuel pumps and turbos than the older F-series cars. If you're not sure, read our B58 Gen 1 vs Gen 2 guide.

Newer cars are where it gets tricky:

  • Cars built after mid-2020. MHD says cars produced after 06/2020 can only be tuned after a special FEMTO unlock, because of BMW's newer tuning protection. That means pulling the DME and sending it out for a bench unlock. MODE, an unlock provider, warns that the DME's production date is not the same as the car's build date. Check the DME itself.
  • Dealer updates. MODE also warns a dealer software update can re-lock the DME. Then you pay for the unlock again. Tell your service advisor you're tuned, or skip the update.
  • 2025+ cars. BMW updated the B58 again for the 2025 M340i, with a 48V mild-hybrid system. Burger Motorsports calls the newer engine B58TU2 / Gen 3 and says it needs its separate Gen 3 B58 JB4.

Our shop-by-car page for the G20 M340i filters parts to your car. For the 4 Series, use /shop?car=g22-m440i. For the G42, use /shop?car=g42-m240i.

The M340i / M440i mod order at a glance

StepMain partsWhat you need firstHonest takeShop
1. Tunebootmod3, MHD or JB4, fresh plugsDME unlock checkBest value on the carbootmod3 tune, Tuning
2. DownpipeCatted downpipe + Stage 2 mapTuneBig midrange jump; louderDownpipes
3. Charge pipeAluminum Gen 2 charge pipeNothingInsurance at higher boostCharge pipes
4. CoolingHeat exchanger, oil cooler, trans coolerNothingA must in Texas heatCooling
5. Intake / exhaustInlet pipe, intake, valved axle-backNothingMostly soundIntakes, Exhaust
6. FuelUpgraded HPFP, flex fuel, E-blendStage 2Where the stock fuel system runs outFueling
7. ChassisTires, pads, springs or coilovers, sway barsNothingDo it as power goes upSuspension, brakes, wheels

Step 1: the tune

The tune is the mod. Everything else supports it. For a full breakdown, see bootmod3 vs MHD vs JB4.

  • bootmod3. Flash tune with off-the-shelf maps and a big custom-tuner network. We sell it: bootmod3 B58 tune. For 2020+ high-output B58 cars like the M340i, bootmod3 lists up to 25% HP and 35% torque for Stage 2 on 93 octane. That's their claim, not our dyno number.
  • MHD. Flash tune with a lower entry price. MHD lists the G20 M340i and G42 M240i as supported. You still need the unlock on newer DMEs.
  • JB4 (Burger Motorsports). A piggyback. It doesn't rewrite the factory software, and it comes off. Burger lists its Gen 1/Gen 2 JB4 for the 2020–2024 M340i and 2021–2024 M440i. It claims up to 120 hp and 120 lb-ft at the wheels on a stock B58 on pump gas. On a car that can't be flashed yet, this is often the answer.

Do fresh plugs before you tune. Gen 2 cars use a different plug than Gen 1, so match the part to your engine.

Step 2: downpipe and a Stage 2 map

A downpipe opens up the exhaust right after the turbo. Stage 2 maps are built around it.

On a G20 or G22, I'd stick with a catted downpipe. It's quieter, it smells better in traffic, and it's kinder to your neighbors. Active Autowerke makes a catted B58 downpipe listed for the G20 and G22.

Expect more drone on the highway. Shop downpipes and ask us about fitment for your build date.

Transmission (ZF 8-speed)

Every M340i and M440i in the US is an automatic. A tuned ZF 8HP feels best with a transmission tune. xHP is the common tool for this. It removes factory torque limits and can speed up shifts.

Step 3: charge pipe

Honest take: at stock-turbo boost, a factory charge pipe failure isn't common. But it's plastic, and it's cheap insurance once you're running a Stage 2 map. Gen 1 and Gen 2 pipes do not swap, so buy the Gen 2 / B58TU version.

Step 4: cooling (do not skip this in Texas)

A tuned G20 in a Dallas summer heat-soaks fast. Intake air temps climb and the tune pulls timing. Cooling won't add peak numbers on a cool day. It keeps you making power on the second and third pull.

Step 5: intake and valved exhaust

On a stock turbo, intakes are mostly about sound. You'll hear the turbo more. Don't expect big power.

The exhaust is the same story: sound, not power. The factory system has valves. Keep them, and you keep a quiet mode for the drive to work.

Step 6: fuel and ethanol

Gen 2 runs a 350-bar direct-injection system, a big step up from Gen 1. Even so, when you push past Stage 2 or run more ethanol, the high-pressure pump becomes the wall. That's when an upgraded Gen 2 HPFP and a flex fuel kit make sense. Talk to your tuner before buying. On Gen 2, more pump can also mean more injector.

Water-methanol is another route for heat and knock. The Snow Performance Stage 3 Boost Cooler kit needs a tune that supports it and a custom install.

Honest take: if you can't buy E85 nearby, a pump-gas Stage 2 M340i is already very fast. Shop fueling.

Step 7: suspension, brakes, wheels and tires

Power is useless if the car can't put it down or stop.

Tires first. A good max-performance summer tire does more for lap times and launches than almost any bolt-on. Get the right size for your wheel and stagger.

Brakes. Start with pads and fresh fluid. EBC Redstuff rear pads are listed for the G20 M340i and G42 M240i. Check your rotor size first.

Springs and sway bars. For a daily, springs and bars are the value move.

Coilovers. Here's the catch: buy for your exact car. Adaptive dampers (EDC) or not, and xDrive or RWD, change the part number.

Wheels. These cars use 5x112. If you want a flusher stance, Dinan 10mm spacers are listed for the M340i, M440i and M240i. Longer lug bolts usually come with spacers.

xDrive vs RWD

xDrive is the launch king. A tuned xDrive M340i or M440i hooks where a RWD car spins. The transfer case uses a clutch pack, and hard launches put heat into it. Fresh fluid is cheap insurance. We carry Red Line MT-LV transfer case fluid and ran it in my M240ix. Always confirm the spec for your car with BMW.

RWD is lighter and more fun on a back road. But a tuned RWD car will spin on the hit. I learned that with my RWD 540i. Plan for tires before power. Red Line 75W85 diff fluid suits stock open diffs on both RWD and xDrive cars.

Where the G42 M240i fits in

The G42 M240i shares the same engine family and a lot of parts with the G20 and G22. Intakes, heat exchangers, the CSF oil cooler, charge pipes and many chassis parts cross over. Always check the listing for "G42" before you buy. Suspension is the big exception: the G42 has its own springs and coilovers.

FAQ

What is the best first mod for an M340i?

A tune. bootmod3, MHD or a JB4. First, check whether your DME needs a bench unlock.

What is M340i Stage 1 vs Stage 2?

Stage 1 is a tune on stock hardware. Stage 2 is a tune built around an aftermarket downpipe.

Should I get a catted downpipe on my M340i?

For a street-driven car, yes. It's quieter and cleaner smelling. It's still an off-road / competition part.

Can I tune a 2025 M340i?

It's harder. The 2025 car uses a newer B58 revision. Burger Motorsports sells a separate Gen 3 JB4 for it. Ask your tuner what's supported for your VIN today.

Do M440i mods fit the M340i?

Many engine parts do. Exhaust and suspension are often body-specific. Check the listing for your exact chassis.

Is xDrive or RWD better for tuning?

xDrive for straight-line launches. RWD if you value lighter steering and a playful car, and you'll budget for tires.

Not sure what fits your car? Shop by vehicle: G20 M340i, G22 M440i, G42 M240i. Or start with our general best B58 mods guide.

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