Despite all that gadgetry, the 8 Series failed to impress as much of a driver’s car back in the day. Though the car’s rakish styling (by Klaus Kapitza) suggested a sports car, the 8 Series was a luxurious grand touring coupe. Those who wanted something more aggressive were left to transform the car themselves, much as Cohen as done with his.
We’ve already mentioned the displacement increase from 4,988cc to 5,944cc in the M70 V12 engine, achieved via a Moldex custom billet crankshaft with an 86mm stroke; lightened, balanced and shot-peened con rods; Wiseco custom forged pistons with 9.36:1 compression.
In addition, the ported and polished cylinder head was given a four-angle valve job and mated with S70 cams and ExtrudeHoned intake manifolds followed by Rinehart custom headers. The throttle bodies were bored out by 3mm and paired with 18.4 lb/hr Bosch injectors. The engine also got custom DME chips from The Powerhouse, a BMW engine oil cooler and a clutch and pressure plate sourced from an 850CSi. At the rear, Cohen installed a 7 Series’ 3.15:1 differential with 50% limited slip. The end result, of course, is that impressive 435 hp and 480.5 lb-ft, up from 295 hp and 332 lb-ft as delivered.
That’s about the limit, Cohen says.
“I think there’s only so far you can go with the V12 because of the exhaust side of the heads. In the head itself, the port comes up and does a 90-degree turn,” he explains. “There was talk of somebody back East building a four-cam set of heads, but it was crazy the amount of money he wanted.”
More power alone isn’t enough to transform an 850i into a sports car, so Cohen made substantial suspension improvements, too: H&R Sport springs, Bilstein shocks, Generation K-Bars anti-roll bars that measure 28.5mm front/19.0mm rear in place of the 24mm/13mm stock bars, M-Wrench camber plates/spring perches and a Strong Strut brace.
When we followed Cohen earlier, it was easy to see that he’d dialed-in the 8 Series about as well as one could. Even at a brisk pace, the car showed very little body roll, looking totally planted through the faster corners as well as the tight stuff. I can’t testify to its balance or agility from behind the wheel, but it was certainly capable of running at speeds that forced the new M6 to earn its keep.