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BMW E24 M635CSi

1986 UK M635CSi from the Orkney Isles.

BMW E24 Six Series - The M6 and M635CSi

There was an E23 745i using the M102 engine, a 3.5 turbo derived from the M30. BMW never fitted this to the six series for two reasons. In the early days the six was seen by many at BMW as more of a luxury car than a powerhouse, the turbo didn't fit this train of thought. Although why the six didn't yet the luxurious seven did is a mystery! Secondly were the engineering costs and the problem of fitting an intercooler into the slightly smaller E24. Personally I find this all fairly surprising. However Alpina and others did build turbo sixes and several individuals have put M102s in their own E24s.

It wasn't until 1984 that the extra power was to come and when it did the result was a BMW legend - the M635CSi. The new car shared it's engine with the E28 M5 saloon. It was derived from the exotic E26 M1 supercar but with more modern fuel injection and a wet sump.

The 286bhp 3.5 litre S38 was an engineering masterpiece. It was BMW's first 4 valve per cylinder production engine and had six individual throttle bodies. The experience to build such an engine had been hard won on the race track in the early 70s with the 3.0CSi. Comparing the power and torque graphs of the S38 and M30 3.5 reveal that most of the gains are higher in the rev range and that torque is actually marginally higher on the M30 at low revs. The fundamental difference is in the change to four valves per cylinder and individual throttle bodies, an engine is basically an air pump and thus the S38 makes it gains above 3500 rpm. Economy was reckoned to be about 15% below that of the 635CSi, not bad for such a race bred engine.

BMW E24 M635CSi

Launch model German M635CSi in glorious Henna Red.

The six was only available as a manual and an LSD was standard fitment. Spring rates were stiffer all round and both anti-roll bars were thicker. It also had larger four pot brakes with ABS, up from the 635CSi's 282mm to 300mm at the front. Visually the only clues to it's identity were a larger front air dam with ribbing at the bottom and a pair of //M badges. 390 TRXs were standard but in practice almost all sold with 415s.

The M car is a usable every day machine when needed, just like the other E24s. It needs a little more in the way of maintenance but nothing excessive. These are not fragile in the way of some Italian exotics and 300,000 mile examples can be found without major engine work. It's not unusual to find cars with 200,000 miles for sale today, they were made to be driven not to be pampered garage queens.

Weight for early examples was listed as 1507kg, around 87 more than a manual 635CSi. But that may include aircon as standard, when I removed the broken a/c from my own 635 I found it weighed a mighty 50kg and was not included in the standard 1420kg figure. Post facelift cars were heavier due to the larger bumpers and Highline trim. In europe even leather was an option.

It's worth noting that racing E24s were based on the 635CSi's M30 engine as the 24 valve S38 was never homologated.

BMW E24 M635CSi S38 engine

S38, the heart of the beast.

Facelift M635CSi

For the big June 1987 facelift the six got the same treatment as the 635CSi, loads of leather and bigger bumpers. It now shared the front bumper with the 635CSi so there were no external differences. Inside it gained a leather dash, door skins and centre console just like the 635CSi Highline. Rear head rests and just about everything else that had been optional became standard fitments.

The Motorsport Edition M635CSi's were rumoured to have perhaps 8bhp more than the usual version but this is hard to verify.

BMW E24 M635CSi

Pre-facelift UK M635CSi, note deeper front spoiler.

The American M6

The Federalised M6 sadly lost a few ponies on the trip across the Atlantic and was sold with 256bhp. It was still a great car and still had the six throttle bodies (on the E36 M3 our American cousins had to make do with one). US deliveries commenced in February 1987 almost three years after europe. 1,767 US examples were produced 252 of which were pre-facelift.

Early cars were heavier than the Euro version (1619kg vs 1507) partly due to the larger bumpers but this difference vanished after the '87 facelift when they were the same on both sides of the pond. In any case quite a few M635CSi's were brought to the States as grey market cars, sacrificing warranty protection in the process for their brave buyers.

US cars didn't get rear headrests as standard in the early years but do seem to have had the rear a/c unit. Standard features on early cars included electric sports seats, heated mirrors, heated door lock, cruise control, stereo (always optional in europe) and ABS. There was no automatic option, quite right too!