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Theory
Model Evolution

1984

Introduction of M635 CSi



Georg Thiele explains his M635 development

Georg Thiele (left) explains his M635 development of the M1 engine to the author at BMW Motorsport in Munich. Note individual throttle butterflies and carefully crafted linkage for the six injection inlet tracts.

D

eveloped by BMW Motorsport a new model made it´s entrance this year — the mighty 635 CSi.

M88/3 engine

The engine, coded M88/3, for the new M-coupe was developed from the 24-valve 3453cc engine that originally powered the mid-engined M1 sports car. The major differences between the M1 engine and the M635 CSi version where in the cylinder heads. The water ways and inlet tracts had to be reworked to suit the 30° slanted installation under the 6 series bonnet (the M1 had it's engine mounted verticaly). The valves, 37 mm inlet and 32 mm exhaust, where the same as well as the 264° camshaft duration. The compression ratio was slightly higher, 10.5:1 compared to 9:1 for the M1. The dry sump lubrication system used in the M1 was replaced with the same wet sump as the standard 635 CSi had.

Together with a refined Bosch ML-Jetronic fuel injection and a Motronic engine management system the M635 CSi got a power source that produced 286 bhp at 6500 rpm and a torque of 250 lb.ft at 4500 rpm.

This is quite amazing since the fuel economy was basicly the same as the 218 bhp 635 CSi, 17 mpg for the 635 CSi and 17.1 mpg for the M635 CSi.

Chassis

The chassis was uprated with 10 mm lower and 15% stiffer springs with specially developed Bilstein gas dampers in all four corners.

1984 M635 CSi. Breaks

Bilstein gas dampers, 300 mm cross-ventilated discs with ATE four-piston calipers.

The antiroll-bars was also a bit thicker to reduce the body roll at the cornering speeds this car was developed for. The front brakes got larger (300 mm x 30 mm) cross-ventilated discs with four-piston calipers from ATE. The rear brakes was basicly the same as of the standard 635 CSi but with pistons with an extra 2mm circumference.

The M635 CSi gearbox was a five speed close ratio Getrag 280/5 with gears arranged in a so called dogleg pattern commonly used by racing cars.

Further back there was a ZF final drive with 25% locking and 3.73 ratio. This final drive was taken from the 7 series and was larger on the outside than the 3.07 used in 635 CSi, so the rear floorplan needed to be reworked to fit the larger final drive. The clutch was basicly the same as on the standard 635 CSi but with a lot stronger springs.

The external differences between the M635 CSi and the standard was minor, a sharp eye could see that the front spoiler was deeper and the fender flares where slightly thinner to accommodate the wider 220/55 Michelin TRX tires on 165 TR 390 alloy wheels or the optional 210 TR 415 BBS three-piece alloy wheels with 240/45 VR Michelin TRX tires.

1984 M635 CSi. Front spoiler
1984 M635 CSi and 635 CSi front spoilers difference

Here the squared off front spoiler and wheel arches are most noticeable, driver's wiper carrying a small aerofiol to complete the conversion!


[an error occurred while processing this directive] BMW Motorsport logotype
1984 6-Series BMW. Headlights

The rear view was the same, except for the M-badge on the trunk lid.

The sporty Recaro front seats was optional for all 6-Series models and also for the M635 CSi. It also had a sportier 3-spoke steering wheel (optional on other models).





1984 M635 CSi. BMW-Sport front seats

INterior improvements include these superb seats with a wide range of adjustment, and a chunky steering wheel to keep them company.


1984 M635 CSi. 3-spoke steering wheel

M635 CSi with it's unique Motorsport three spokes steering wheel. «The harder you drive, the better the M635 becomes...»





Other 6-series models

Only minor changes where made on the other 6-series models. The headlights where new with two-stage reflectors that improved headlight intensity directly in front of the car, optional was a so called dip-beam headlight system that made it possible to change (dip) the headlights from the drivers seat when the car was carrying extra load.

The 635 CSi got the fog lamps integrated with the front spoiler.

1984 6-Series BMW. Fog lamps

New auto-gearbox

New and only available in the 635 CSi was a 4-speed automatic gearbox with a electronic/hydraulic control that allowed the driver to choose individual driving programmes for sport, economy or semi-manual lockup for slippery winter roads.

1984 6-Series BMW. 4-speed automatic gearbox

The programmable 4-speed automatic gearbox. Three programmes available: sport, economy and semi-manual lockup.

Interior

The interior was almost unchanged, except for a new 3 spoke steering wheel and a new 8 function OBC (On-Board Computer), the OBC was still optional in the cheaper 628 CSi.

633 CSi

This was the last year for the US version of 633 CSi.

Production numbers for 1984

Model Units
628 CSi 401
628 CSi A 191
628 CSi RHD 35
628 CSi A RHD 114
633 CSi USA 1173
633 CSi A USA 776
633 CSi A Japan 58
635 CSi 1365
635 CSi A 962
635 CSi RHD 72
635 CSi A RHD 475
635 CSi USA 695
635 CSi A USA 532
635 CSi A Japan 2
M635 CSi 1404
M635 CSi RHD 8
Total: 8263

Source: Bmwcoupe.nu

Content

Home





See also

3453cc engine in M635 CSi


M88 engine in BMW M1


M635 CSi technical information


Check Control panel


On-board computer


Comments

hi, Paul!
I'm sorry but personaly I don't have any special info about turbo. I think the only way to find anything useful is ETK.
// dnd


Hi, I have a U.S. 1984 (built 10 of 1983) 633 csi TURBO, I am having trouble finding any info on this turbo !
it looks factory with a matching Turbo emblem on the back pass side and the unit itself reads CARTECH as well as the boost gauge. Can you give me any info on this car? or its turbo origin? Thank You.
Paul
// Paul Kruger


Hmm.. may be owners have installed them later?
Or may be the point is that september 1983 is actually the new 1984 model year...
By the way i really appreciate you for all your corrections! Unfortunately i don't have your email address to thank you.
// dnd


I'm not sure 1984 was the first year the Euro 635csi had the foglights integrated into the air-dam. I see 3 1983 635csi's in the owner's section with fogs integrated in the air-dam. // Adrian


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