The main market for BMW vehicles with the N62 engine in our Plus 8s was the USA. Unsurprisingly, there are web posts on tuning these engines: in our cars they produce 362 bhp, at the high end of the output range for the N62
I believe there have been efforts to produce a 4 into 2 into 1 manifold, but there simply isn't room.
Alpina developed, with BMW, the H1, a version of the N62B44: Changes to the engine include an Alpina specific block, a forged crankshaft and high strength Mahle pistons and the addition of an ASA centrifugal supercharger. The motor's combustion process was optimized by changing the camshaft. This resulted in a significantly lower exhaust gas temperature, which is the basis for the performance increase. The power of the 4.4-liter V8 was thus increased by 22 kW (30 PS; 30 hp) to 390 kW (530 PS; 523 hp). The torque increased by 25 N⋅m (18 ft⋅lbf) to 725 N⋅m (535 ft⋅lbf). The B5 S takes the sprint to 100 km/h (62 mph) in 4.6 seconds; The top speed increases to 317 km/h (197 mph)
But in the light weight Plus 8 the 0-62 mph time is about the same as the H1 version in a heavy BMW 5 series.
Such engines are not cheap, and to be honest, why would anyone want that amount of power in a Plus 8 with no traction control or stability control?
I also wonder if the engine would fit into the S4 Aero Chassis as used on the Plus 8.
