1987-1988 M6Jeremy Walton, author of the BMW 6 Series Enthusiast's Companion, offers two reasons in his book for the delay in introducing the M635CSi to the American market: BMW did not perceive a market for a more muscular 635CSi in the United States, and had difficulties engineering an emissions-certified version of the hellacious twin-cam engine. This explanation comports with what we knew about BMW in the 1980s, which is that the Germans could not understand why Americans would want high-powered cars given the 55-mph national speed limit at the time, which was laughably slow in Europe. The notion that there could be wholesale disregard of the law was inconceivable to the law-and-order Germanic mindset.
The detuning necessary to meet U.S. emissions regulations pared the M88 down to 256 bhp by a reduction in compression ratio to 9.8:1 vs. Europe's 10.5:1, the addition of a catalytic converter, and engine management software tweaking. Thing was, most American Bimmerheads didn't really have a frame of reference for what was lost. Applying a classic trick from the '80s, BMW lowered the U.S. differential ratio to 3.91 to compensate for the lower power output of the smog-compliant engine.
The coil springs were slightly softer, and slightly higher to meet U.S. bumper height regulations. The M6 bumpers were the big aluminum units, BMW's "world bumpers" being one year away. The M6 used firmly-valved BOGE shocks at front in place of Europe's Bilsteins, and the rear used BMW's hydraulic self-leveling shocks. The system was great but complex, and replacement parts are very expensive. When a component fails in the M6 self-leveling rear suspension system, that's often when the car gets converted to Bilsteins and conventional or aftermarket sport springs.
We got more sedate color options here, as always, and gone were the cool European stripes. The exhaust note was quite a bit mellower, and unfortunately the dreaded TRX wheels and tires remained unaltered in the U.S. transformation.
The M6, as it was known in the U.S., was everything the M635CSi was only less. Still, it is still a very hot '80s ride and much can be done to improve power. For example, a Conforti chip bumps power by 48 hp and 32 lb-ft, thus recouping the loss from factory detuning and then some. The chip also affords a 7200 rpm redline, which you are well advised not to use; keep the M88 to 7000 rpm or lower to keep it together, especially the crankshaft balancer. And plan on using at least 93 octane fuel. Live in California? Forget the chip. It's legal, but your gasoline does not have sufficient octane unless you're willing to mix it with racing fuel.
Buying an M635CSi or M6The key thing to remember about buying either one of these cars is that parts unique to the M version of any BMW will cost at least twice as much as those on its non-M sibling. This includes engine parts, exhaust parts, the manual gearbox, clutch parts, body parts and brake parts. The M88 engine is a thinly disguised race plant, and it requires high maintenance. A minor tune-up is recommended every 15,000 miles, including replacing the special Bosch X5DC spark plugs and a shimmed valve adjustment. If the gearbox and differential oil were never changed, you may be looking at very expensive rebuilds. Rebuilding the engine will cost a minimum of $10,000.
Service information for both cars is contained in the BMW Mobile Tradition E24 6 Series Repair CD, BMW part number 01 56 0 030 285. Parts information can be found in the BMW Mobile Tradition Historic Vehicle and Historic Motorcycle Parts Catalog CD, BMW part number 72 00 0 301 255.
The M635CSi requires extra care when purchasing. Installation of a functioning catalytic converter to "pass emissions" usually means the engine will be on its last legs; the high compression and rich mixture, combined with the early engine management system, are incompatible with a catalytic converter over the long term. And paying for the rebuild is sometimes easier than finding a qualified technician to perform it. But if you talk to an owner of one of these cars, including our own Dan Erwin, he'll tell you that, in the end, it's all worth it because nothing quite compares to an M635CSi... unless you have an M1.
Recommended ReadingBMW 6 Series Enthusiast's CompanionBentley Publishers (www.bentleypublishers.com)
The New BMW M6Munich builds a better JaguarDuring the tenure of former Cosmopolitan editor Helen Gurley Brown, the concept of sex found its way onto each cover. Brown believed (and correctly so) that sex would help sell the issue, even if it was bad sex (if there is such a thing).
That said, you will find the new M6 on the cover of this mag. It is hands down the sexiest car in BMW's aresenal. The new M6 will make you more attractive to the opposite sex and improve your love life tenfold. It will whisper words that every man and woman wants to hear and unlock secret passions within (desperate newsstand trick).
While I'm sure BMW could sell more than a few M6s based on the car's aphrodisiacal qualities, the sexiest component of this car is how well it drives. Imagine a supermodel, quantum physicist and decathlete all rolled into one. That is the new M6.
Although it is no fluke the M6 makes 507 bhp (remember the gorgeous BMW 507s of yore?), a quick stab of the throttle reveals a car nothing like its older sibling. Seated within the deep confines of the body-contoured M sport seats, the sensation is more like being in an F-14 cockpit complete with a heads-up display. Whereas the 507 provided a more visceral experience (screaming engine, wind-in-hair, etc.) the M6 is all about powerful understatement. You become acutely aware of the physics of high speed-forward thrust, lateral g-forces and brutal deceleration. More often than not, I heard my own heart beating on the Ascari Race in Spain, a 2.5-mile playground for the rich and very rich.
It takes a lot of chutzpa for a manufacturer to loose luxury street cars on pavement made for Spartan racers. I doubt very few M6 cars will ever see this type of activity and that's a shame, because they behave as though they were bred for it.