Seeking advice DIY tuning F-Series N55 - Overboosting


New Member
Jan 8, 2020
Hi guys, I'm new to the forum. I've been looking for information on how to properly go about tuning the late N55 motor (version without commanded WG) for a while, I've done some experimentation but still have a few issues to iron out. Some guidance or links to good resources would be greatly appreciated!

For context I'm running a F21 M135i EWG with FBO and the 8AT flashed.

I started off by taking a log of the stock tune to use as my base. I recorded a peak boost of 9psi (oof). Then I set 'Limitation by automatic gearbox' to 3 which is meant to disable TCU torque limits in the DME. I also set 'Torque request ceiling (Auto)' to 510 across the board, as well as 'Modelled torque limit 1, 2' to 510 across the board. Finally I set 'Boost limit multiplier 1, 2' to 3 across the board.

This increased my peak boost to 11psi, but at WOT Boost (pre-throttle) rises above the boost target and causes throttle closure. Do I just need to increase the Boost limit multiplier again, or am I missing something else?
Last edited:


New Member
Jan 8, 2020
Unless you just didnt mention it. You forgot to increase Load Ceiling as well.
In case I'm mislabelling things here's the full extent of my changes, if the table isn't on here I didn't change it. I've tried limitation by automatic gearbox set to 3 too with no difference. Am I missing something?

things I changed.jpg


Jan 23, 2018
I suggest you start with this:
. EcuTek's N55 tuning tutorial is a great intro to N55 tuning. The table names differ slightly between EcuTek and BM3, but they're easy enough to figure out.
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