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E24 M635CSi/M6





Production Versions:

5531: European-spec (LHD), 12/83-12/88
5511: European-spec with catalyst (LHD), 11/86-12/88
5532: European-spec (RHD), 09/84-02/89
5514: North American-spec (LHD), 09/86-09/88
5519: Japanese-spec (LHD), 09/86-03/88




History

What makes the M6535CSi/M6 unique?
The M635CSi and M6 are the BMW Motorsport-developed versions of the E24 6 Series. They use the M88 or S38 twin-cam 24-valve inline-six-cylinder engines first introduced in the M1. They also have a BMW Motorsport-tuned chassis and a few special cosmetic pieces.

What’s the difference between the M635CSi and M6?
All examples of the BMW Motorsport-developed E24 6 Series are known interanlly as the M635CSi. However, all North American versions were officially badged "M6", both to simplify the name and to bring it in line with the other M models, specifically the M3 and M5.

When was the M635CSi/M6 first introduced?
The M635CSi was introduced at the 1983 Frankfurt Motor Show.

Where was the M635CSi/M6 built?
Like all 6 Series, the M635CSi/M6 was built on the normal Dingolfing assembly line, with body shells shipped from the Karmann works in Osnabruck.



Production Data

How many versions of the M635CSi/M6 were developed?
BMW Motorsport developed five different versions of the M635CSi/M6: Two non-catalyst models for the European market (left-hand drive and right-hand drive), plus three distinct catalyst versions for Europe, North America and Japan (all left-hand drive).

How many of each version were produced?
ECE (LHD without cat): 3,283 built from 12/83 thru 12/88
ECE (RHD without cat): 524 built from 09/84 thru 02/89
ECE (LHD with cat): 117 built from 11/86 thru 12/88
NA (LHD with cat): 1,767 built from 09/86 thru 09/88
JAP (LHD with cat): 164 built from 09/86 thru 03/88

What changed during the production of the M635CSi?
There were few major mechanical changes during the five-year period that the M635CSi was produced, though certain items with known mechanical defects (valve springs, two-piece wheels) were updated during the course of production. In addition, the catalyst-equipped S38 engine became available as an option in some left-hand drive European markets starting with November 1986 production (two months after it became the standard M6 engine in North America). Also beginning in 1986, a fixed rear center console with integrated storage compartment and air conditioning unit became available in some markets and Shadowline (dechromed) exterior trim was added to the option list.

The biggest cosmetic changes occurred starting with June 1987 production. At this time, the slimmer chrome-trimmed bumpers were replaced with larger versions featuring body-color end caps. Also, ellipsoid headlights and foglights replaced the halogen units of earlier cars. The latter were part of a reshaped front airdam that was shared with the regular 635CSi. Finally, the shift knob was updated to the ergonomic design introduced a year earlier on the E32 7 Series, and the Highline complete Nappa leather interior, already standard on U.S.-spec M6s, became available as an option in other markets. (Note: All right-hand drive examples of the "big bumper" M635CSi have the Highline Nappa leather interior.) The final change occured in Spetember of 1988 when the power front seat controls were moved from the center console to the base of the seat itself.

How did these changes affect the North American M6?
Though there were no major mechanical alterations during the production of the North American M6, the are a number of cosmetic differences between M6s built before June of 1987 (1987 models) and those built after that date (1988 models). The 1987 models have large, government-mandated five-mph bumpers with black rubber trim and a unique front air dam that is similar to that of the 1985-87 North American-spec 635CSi, but with extra cooling ducts for the engine oil cooler. The 1988 model features the same updated bumpers, ellipsoid headlights and revised front airdam with flush-mounted foglights as the facelifted, European-spec M635CSi. It also has the ergonomic shift knob. U.S.-specification M6s built to 1988 specification are further fitted with a driver-side airbag with knee bolster, but lack the leather dashboard and upper door trim of the 1987 M6 Highline models (though they retain Nappa leather upholstery on the seats, center console, lower door panels, glovebox door, A-pillars, B-pillars, headliner and sun visors).



Drivetrain

What makes the M88/S38 engine unique?
The M88 and S38 engines are evolutions of the 24-valve inline-six developed for the mid-engine M1 supercar. Like that engine, both the M88 and S38 have a four-valve crossflow cylinder head (with 37mm inlet valves and 32mm exhaust valves) designed for better breathing at high rpm and a pair of 264-degree camshafts. They also share a displacement of 3,453cc via a bore of 93.4mm and a stroke of 84mm. However, for their application in the M635CSi/M6, the M88 and S38 have unique pistons and connecting rods, as well as a more advanced Bosch ML-Jetronic fuel injection system. To save costs, both engines utilize the standard steel M30 crankshaft and wet-sump lubrication system. Many other smaller items, such as the ignition system, are shared with the regular 6 Series as well.

How do the M88 and S38 engines differ?
The M88 is the non-catalyst version of the S38 engine. With a 10.5:1 compression ratio and a single-row timing chain, it is identical to the one found in Euro-spec E28 M5 sedans. Power is rated at 286 hp (DIN) at 6,500 rpm with 251 lb/ft of torque at 4,500 rpm. The M88 can be identified by the inscription on its cam cover: the propeller Roundel plus the words “BMW” or “M Power.”

The S38 is the “clean” version of the engine, introduced for North America but later offered in other markets as well. It utilizes a duplex (double-row) timing chain and lower 9.8:1 compression designed to work with catalytic converters. This reduced the horsepower to 256 hp (SAE) or 260 hp (DIN) at 6,500 rpm and torque to 243 lb/ft at 4,500 rpm. The S38 has the inscription “BMW M Power” on its cam cover but no Roundel.

What kind of gearbox does the M635CSi/M6 have?
All M635CSi/M6s have the Getrag 280/5 five-speed manual gearbox. Gear ratios are as follows: 3.51 (1), 2.08 (2), 1.35 (3), 1.00 (4), .81 (5). A 3.73:1 final drive is fitted to all but the North American M6, which uses a 3.91:1 rear end. All have limited slip differentials with a maximum locking of 25 percent.



Chassis

How is the M635CSi/M6's suspension different from the standard 6 Series?
All M635CSi/M6s use the MacPherson strut/semi-trailing arm suspension design common to all E24 6 Series. However, it has been tuned by BMW Motorsport in the following ways:
-Ride height reduced by 0.4 inches
-Increased steering caster
-Spring stiffness increased by 15 percent
-Progressive rate rear springs
-Specially-tuned Bilstein shocks

A self-leveling rear suspension was optional in some markets and standard on all North American-spec M6s.

How is the M635CSi/M6's steering different from the standard 6 Series?
The M635CSi/M6’s recirculating ball steering with ZF power assist is identical to the one used in the regular 635CSi and has an overall ratio of 15.7:1. Like the 635CSi, cars built for the final 1989 model year have vehicle-speed sensitive Servotronic power steering made by ZF.

What size brakes does the M635CSi/M6 have?
The M635CSi/M6 has enlarged vented front rotors that measure 11.8-inches (300mm) in diameter. These utilize four-piston calipers. The solid rear rotors, measuring 11.2-inches (284mm) in diameter, are the same as those found on the 635CSi. ABS is standard.

What are the factory wheel and tire sizes for the M635CSi/M6?
There were two available wheel and tire sizes for the M635CSi. Early European-spec cars used the standard 6 Series metric-sized wheels (390mm x 165mm) with 220/55VR390 Michelin TRX tires. However, optional from the start of production (standard in some markets) were larger, two-piece alloys in a cross-spoke design measuring 415mm x 195mm (16.3-in. x 7.7-in.). Cars with these wheels carry 240/45VR415 Michelin TRX tires. After the two-piece wheels showed signs of cracking, BMW switched to a similar one-piece cross-spoke design in the same size as part of the June, 1987 facelift. However, these wheels were also fitted to all North American M6s from the beginning of production.



Cosmetics

What distinguishes an M635CSi’s exterior from a regular 6 Series?
The M635CSi has few visual clues to distinguish it from the normal 6 Series. Almost all body panels are shared with other E24s, including the body-color rear spoiler with black rubber lip. The only exception is the deeper front airdam fitted only to pre-facelift models, which is ribbed on the lower portion. There are also two M badges, one on the trunklid and one on the grille, though these could be omitted upon request. In addition, the rear-view mirror housings are painted in body color instead of the chrome finish used on all other pre-facelift 6 Series. Finally, cars with the BBS-style cross-spoke wheels (in either the early or later version) have body-color fender lip extensions. After the mid-1987 facelift, the front airdam was changed to the same one fitted to all 6 Series, so the M635CSi could only be identified by its M badges (where fitted) and 415mm (16.3-inch) cross-spoke alloys, now standard and in a one-piece design. As with the 635CSi, Shadowline (dechromed) exterior trim became optional on the M635CSi during 1986 but only with limited exterior colors.

What distinguishes the exterior of the North American M6 from that of the M635CSi?
Cosmetically, all North American-spec M6s have unique grille and decklid badges with the “M6” logo. They also have a rear spoiler (not fitted by the factory to other North American 6 Series models) and the later one-piece metric-sized cross-spoke alloy wheels. Cars built for the 1987 model year (before June, 1987 production) have the bulky five-mph bumpers used on all 1978-87 6 Series in North America. The 1987 M6 also has a unique front airdam, with additional cooling slats. Cars built for the 1988 model year (6/87 and later) have ellipsoid headlights and a slimmer 2.5-mph bumper design that is visually identical to the European-spec M635CSi of the same vintage. The front airdam on these cars is also identical to the one used on all 1988-89 6 Series. All North American M6s have chrome (non-Shadowline) exterior trim.

What distinguishes an M635CSi’s interior from that of a regular 6 Series?
The interior of the M635CSi is much like that of all other 6 Series models. The only truely unique item is the instrument cluster, which contains a 280 kph/170 mph speedometer and a special tachometer with the M logo instead of an economy meter. In addition, every M635CSi is fitted with the three-spoke M-Technic steering wheel (unless equipped with the optional driver's airbag) and the same sport seats available in other 6 Series models. In some markets, these could be replaced by the wider "comfort" chairs, also shared with other 6 Series models. Finally, the battery of the M635CSi is mounted in the trunk for better weight distribution.

How does the interior of the North American M6 differ from that of an M635CSi?
The M6 interior differs little from that of the M635CSi. Like the European model, North American examples have the unique instrument cluster with a 280 kph/170 mph speedometer and a special tachometer with the M logo. However, they also have a generally higher level of standard equipment, including leather sport seats with power controls and driver’s side seat memory, power sunroof, cruise control, air conditioning, rear window sunshade and an eight-speaker am/fm cassette sound system. U.S.-spec cars are further enhanced by Nappa leather upholstery with either the Highline (1987 models) or Halfline (1988 models) interior trim and a rear center console/air conditioning unit. On 1988 models, a driver’s side airbag is also standard for U.S.-spec examples. Heated front seats were standard on the Canadian-specification M6 and the sole factory option on U.S models.

How exactly are U.S-specification and Canadian-specification M6s different?
All North American M6s are mechanically identical. They also have the same exterior appearance (with the exception of two additional exterior color choices for Canada). It is only on the inside that the U.S. and Canadian models can be distinguished from each other. The following are all the ways that the two versions differ, aside from having metric (Canada) or non-metric (U.S.) instrumentation:

U.S Specification:
Leather trim: Nappa Highline leather (1987) or Nappa Halfline leather (1988)
Rear console with A/C unit: Standard
Heated front seats: Optional
Driver’s side airbag with knee bolster: Standard (1988 models only)

Canadian Specification:
Leather trim: Regular leather on seats only
Rear console with A/C unit: Not available
Heated front seats: Standard
Driver’s side airbag with knee bolster: Not available

What are the Highline and Halfline interiors?
To add additional luxury to the M635CSi late in its product cycle, BMW introduced a Highline interior option as part of the mid-1987 facelift. It is worth noting that all left-hand drive facelifted examples are not necessarily Highlines, as they are often incorrectly referred to. In other words, there are a small number of left-hand drive facelifted cars without the Highline interior option.

The Highline interior includes hand-stitched Nappa leather on the seats, door panels, center console, glovebox door, headliner, sun visors, door pillars, upper door trim and dashboard. This interior was standard on all U.S-specification M6s built before June 1987, as well as all "big bumper" UK-specification M635CSi examples. In some other markets, the Highline interior could be ordered as an extra-cost option.

A special variation of the Highline linterior was introduced on all U.S.-specification M6s beginning with June 1987 production (1988 model year) after BMW of North America was forced to replace a significant amount of 1987 M6 leather dashboards that had been warped by the sun in warmer parts of the United States. Unofficially known as the "Halfline" interior, it included all the Nappa leather trim of the Highline interior except for the leather dashboard and leather upper door trim.

What features were optional on the M635CSi?
In general, the level of standard equipment increased on the M635CSi from year to year. Depending on the market and production date, options included: cross-spoke alloy wheels, metallic paint, Shadowline (dechromed) exterior trim, headlight washer/wipers, leather upholstery, air conditioning, rear air conditioning and storage unit, power front seats with driver's side memory, heated front seats, power sunroof, rear window sunshade, rear headrests, and various audio systems.



Special Versions

Were there any special editions of the M635CSi/M6?
There were no official special editions of the E24 M635CSi or M6. However, BMW United Kingdom offered an unofficial "Motorsport Edition" of the 1989 M635CSi in three special color and trim combinations: Misano Red (236) with Black Nappa Highline leather upholstery, Nogaro Silver metallic (243) with Black Nappa Highline leather upholstery and Macao Blue metallic (250) with Lotus White Nappa Highline leather upholstery. Produced in one consecutive batch of 23 examples between October of 1988 and February of 1989, the "Motorsport Edition" included all of the standard UK M635CSi equipment, plus Shadowline exterior trim and M stripe lapels on the front and rear seats.

Though not technically a special edition, the last two examples of the North American M6 ever produced are unique in that they were the only two made for the 1989 model year. Both VIN 2561766 (Alpine White II with Black leather) and VIN 2561767 (Salmon Silver with Black leather) were equipped to Canadian specification and feature the later E34-style power seat controls mounted directly to the seat instead of on the center console.




Color and Upholstery Selections

Exterior Colors (M635CSi):
Alpine White (146), Alpine White II (218), Henna Red (052), Cinnabar Red (138), Lapis Blue (173), Saturn Blue (176), Atalantis Blue (207), Mineral Blue (231), Crimson Red (172), Wine Red (224), Black (086), Polaris Silver metallic (060), Salmon Silver metallic (203), Bronzit metallic (139), Sable Brown metallic (196), Luxor Beige metallic (219), Burgandy metallic (199), Burgandy II metallic (214), Graphite (087), Delphin Grey metallic (184), Saphire Blue metallic (149), Baltic Blue metallic (178), Cosmos Blue metallic (185), Cirrus Blue metallic (189), Royal Blue metallic (198), Emerald Green metallic (182), Malachite Green metallic (205), Diamond Black metallic (181)

Note: Availability of colors varies by market and production date

Interior Colors (M635CSi):
Pearl Beige cloth, Nutria cloth, Natur cloth, Anthracite cloth, Silver cloth, Pacific Blue cloth, Indigo cloth, Pine Green cloth, Pearl Beige leather, Lama leather, Nutria leather, Black leather, Pacific Blue leather, Silver leather, Cardinal Red leather, Nutria Buffalo leather, Anthracite Buffalo leather, Simagrey Buffalo leather, Havanna Buffalo leather, Lotus White Nappa leather, Black Nappa leather, Silvergrey Nappa leather, Natur Nappa leather

Note: Availability of colors and materials varies by market and production date

Exterior Colors (M6, U.S.-specification):
Black (086), Cinnabar Red (138), Royal Blue metallic (198)

Interior Colors (M6, U.S.-specification):
Lotus White Nappa leather, Natur Nappa leather, Silvergrey Nappa leather
NOTE: Black Nappa leather offered on very late-production 1988 models

Note: Cars produced before 6/87 (1987 model-year) are equipped with a complete (Highline) leather interior including hide on the seats, dashboard, center console, glovebox door, A-pillar, sun visors, headliner, upper door trim and door pulls. Cars produced after 6/87 (1988 model-year) have an extended (Halfline) leather interior which does NOT include hide on the dashboard or upper door trim.


Exterior Colors (M6, Canadian-specification):
Alpine White (146), Cinnabar Red (138), Black (086), Royal Blue metallic (198), Salmon Silver metallic (203)

Interior Colors (M6, Canadian-specification):
Black leather, Silvergrey leather, Pearl Beige leather (thru 5/87), Natur leather (from 6/87), Indigo leather