B58 without question. Its everything the N55 is but better. More power stock, better fuel economy, stronger internals, and it responds incredibly well to tuning.
The N55 is great but the B58 is a generational leap. The closed deck block alone makes it significantly stronger.
B58 for reliability, N55 for simplicity. The B58 has more electronic complexity which means more potential failure points down the road. But mechanically its superior.
For a stage 1 tune the B58 makes silly power. Like 380-400 hp with just a flash. The N55 tops out around 340-350 hp on stage 1.
I've tuned both extensively. The B58 is the better engine in every measurable way. But the N55 has a certain character that the B58 lacks - the turbo spool, the exhaust note, the rawness.
If youre buying with your head, B58. If youre buying with your heart, N55.
went from N55 335i to B58 340i. zero regrets. the B58 is smoother, more powerful, more efficient, and just as tuneable. plus the 340i has the updated interior and tech which makes a big difference for daily driving.
