MBT stands for Maximum Brake Torque timing. Meaning that the ignition timing is at such an angle so as to provide the highest BMEP (brake mean exerted pressure) on the piston top, and that the crank is at an optimal angle to provide the
most leverage and deliver maximum torque over the broadest range of crank angle. This is measured with an accurate chassis or engine dyno. Ignition too advanced can cause high cylinder pressures and undue stress on rod bearings while not advanced enough timing can cause high EGTs and low torque. There is a book to be written on the topic of ignition timing, so I’ll stop now! Most small turbo, pump-fueled engines will be knock limited at even modest boost levels.