3 stage intake manifold or a varible length intake manifold.
Remember resonance from highschool physics? Yes...especially motorheads should have paid closer attention in physics not just chemistry
the 2 stage system is found on most 128s & 328s, except those produced to meet CARB SULEV standards. Those cars come with a 3 stage manifold.
BMW's DISA (Differentiated Intake System Air) system was first introduced to the N52 V8 engines on 7-Series in 2001. It is the world's first continuously variable length intake manifold.
The principle is simple. The intake manifold of each cylinder is arranged in circular shape and half-recessed into the V-valley. The inner wall is actually a rotor, on which the air inlet is located. When the rotor swivels, the position of the air inlet moves in relation to the outer housing of manifold. This varies the effective length of the intake manifold, from a maximum 673 mm to 231 mm.
Below 3500 rpm, the DISA uses the maximum manifold length to optimize low-end torque. Beyond 3500 rpm, the length is reduced gradually according to rev, keeping the supercharging effect at optimum level.
As the DISA requires a circular construction, it occupies more space (especially height) than other VLIM systems. This prevent it from becoming popular. Even BMW itself was not keen on the technology. When the 4.4-liter V8 was enlarged to 4.8 liters, its extra torque allowed BMW to abandon the DISA for a simpler 2-stage VLIM system. The next generation V8 even switched to turbocharging, so DISA has no hope to return. Today, it remains to be the only continuous variable intake manifold ever made to production.