1988 635CSi

Buyer's Guide: BMW E24 6 Series
For many, the big coupe is the ultimate of Munich's driving machines
From the February, 2009 issue of European Car
By Mike Miller

Finally, Vindication
BMW enthusiasts danced in streets all across America for the 1987-88 model year. In a one, two, three punch, BMW of North America brought us the M3, M5 and M6 in rapid succession. Investments were sold. Mortgages were assumed. Work hours were increased. Marriages were dissolved. Power-starved Americans needed M cars.

While in what by then had become true to form, the U.S.-spec M6 represented a severely detuned version of the fire-breathing European M635CSi, but the fact remained that we now had the real double overhead cam engine. We lived with the fact that it was reduced to 9.8:1 CR, producing 256 bhp at 6500 rpm and 243 lb-ft of torque at 4500 rpm versus the 10.5:1 European version's 286 bhp and 251 lb-ft of torque at the same engine speeds. Later, Mr. Conforti would help our numbers out quite a bit with the simple addition of a chip--and Sunoco 94 octane gasoline in those fortunate areas of the country that have it.

The final 635CSi version marks the pinnacle of non-M U.S. E24 performance. Advances in Bosch Motronic technology allowed a compression ratio increase to 9.0:1, resulting in 208 bhp at 5700 rpm and 225 lb-ft of torque at 4000 rpm. U.S. enthusiasts were finally vindicated with something at least approaching rest-of-the-world performance as the venerable M30 engine soldiered on into the 1990s, durable and dependable as ever.

But the hard edge present in the 1985-87 635CSi was softened for 1988-89. The E24 took a decidedly luxurious turn in the U.S., a marked departure from its road-burning personality elsewhere. Almost all had automatic transmissions, even though the L6 was nixed in favor of universally increased leather content. Rear seat air conditioning and a cigarette lighter coddled passengers, while the center armrest became an air conditioning-cooled beer cooler that was perfect for those long road trips through Texas. A 3.64 differential ratio helped even things out.

Outside, the big news was BMW's switch to "world" bumpers for the 1988 model year, relegatingwThe second-generation (E-28) U.S. 635CSi and among the most common 6ers still found on the road. This example junked its TRX wheels and tires in favor of Hartge alloys. the previous big aluminum units to the history books. The TRX scourge continued unabated, but ellipsoid technology headlights allowed a slight improvement for U.S.-legal headlight efficiency. Unfortunately, U.S.-spec ellipsoid halogens still fell far short of the Hella H1/H4 headlights used in the rest of the world and commonly fitted by those in the know here as well. Double unfortunately, H1/H4s did not fit in the ellipsoid headlight buckets.

BMW's self-leveling rear suspension now found its way into the U.S.-spec 635CSi, using a complex electro-hydraulic system to maintain rear ride height regardless of squat, dive or vehicle load. The system works quite well but is very pricey to repair in its old age. Confronted with the need for new rear shocks or a hydraulic pump, many owners simply convert the car to a conventional rear suspension. This involves capping the hydraulic lines, disconnecting the electrical harness and fitting "normal" rear shocks and non-self-leveling rear coil springs. Many unknowing or simply cheap owners and techs leave the self-leveling rear springs in place. This results in very strange handling and inordinately low rear ride height.

All in all, though, the 1988-89 635CSi remains the enthusiast sixer of choice, save for the M6, for the simple reason of its higher compression engine.

A beefier Getrag 280 five-speed overdrive manual gearbox graced the M6, as did a lower 3.91 limited-slip differential. Larger brakes augmented grip from 240/45VR-415 Michelin TRX tires mounted on lovely-but-worthless-today BBS RS three-piece alloy TRX wheels. Inside, sport seats were standard. Outside, a Motorsport rear spoiler provided downforce on the rear suspension.

The M6 is the ultimate U.S.-spec E24 6 Series although still overshadowed in collector appeal by European-version 6ers.