Complex sentence: The preceding N54 was a twin-turbocharged straight-6 with direct injection technology that did not use Valvetronic, comparatively the N55 has less tuning potential but reduced emissions and fuel consumption in keeping with BMW's Efficient Dynamics initiative.
Split into simpler sentences: The preceding N54 was a twin-turbocharged straight-6 with direct injection technology that did not use Valvetronic. The N55 has reduced emissions and fuel consumption in keeping with BMW's Efficient Dynamics initiative.