B58-Swapped BMW i8 (AWD)

Build by Trevor Elam

Donor car: 2017 BMW 340i · B58 3.0L turbo I6 + full xDrive · Target ~700 hp

The concept

So I found out about the craziest BMW build ever — someone's ripping the entire hybrid system out of an i8 and swapping in a B58 with xDrive. The donor is a 2017 340i. They're pulling the B58 3.0 turbo six, the whole xDrive setup, and all the electronics. Endgame is around 700 hp — insane compared to stock.

Here's the wild part: the i8 normally has that little 3-cylinder in the back, plus an electric motor up front, plus a battery running down the middle of the car. All of that's getting deleted. The B58 goes up front where the electric motor used to live, and they're using the old battery tunnel space to fit the transmission, transfer case, and everything needed to keep AWD.

The real challenge: a custom subframe

The real challenge isn't even the engine swap — it's building a subframe from scratch, since nothing about this chassis was made for a drivetrain like this. They're fully fabricating a custom front subframe to hold the B58 at the right angle, keep the suspension geometry correct, clear everything, and tie into the i8's existing mounting points. Not a stock 3-series subframe — full custom work to play nice with the carbon/aluminum tub.

Keeping full xDrive

Drivetrain-wise they want to keep full xDrive instead of going RWD. So it's B58 → ZF 8-speed → transfer case → front diff/axles → rear shaft → rear diff. That old battery tunnel ends up being clutch — it gives them a channel to run everything through.

Cooling & packaging

Cooling is a whole thing too, since cramming a turbo six up front messes with weight balance. The plan is to put cooling components in the back where the old 3-cylinder and hybrid gear used to sit — custom lines, intercooler piping, heat shielding, exhaust running front to back, all of it.

Still to finish

Right now they're still in the mockup/fab stage. Still on the list:

• Mounting the engine / trans / transfer case for real
• Custom axles and driveshaft
• Rear diff and subframe integration
• Cooling routing and radiator placement
• Fuel system upgrades
• Full exhaust build
• ECU, trans control, and CAN bus wiring
• Suspension and brake upgrades plus alignment
• Tuning everything to hit that 700 hp goal

The i8 was built around hybrid tech from the jump — not a turbo inline six — so this is less of a swap and more like reinventing the whole car as a B58-powered AWD monster wearing the i8 body. Wild project.

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