1985 BMW M635CSi

The BMW E24 M635CSi was in production from 1983 until 1989. Styled in house by Paul Bracq, it is a front-engine, rear wheel drive coupe seating four adults.

The M635CSi was the first true M-upgrade from the in house Motorsport division – broadly, it took the already powerful 635CSi, and fitted it with a derivative of the M88 engine tuned for high performance – the M88/3. This engine was basically a detuned version of that which had served in BMW’s ate 1970s supercar, the M1. This was coupled to a five speed manual gearbox. It’s important to note that American and Japanese specification cars used a different engine, the S88, with 256bhp instead of the European 282. These cars were also badged as M6, rather than the European M635CSi. The engine difference means that as well as being worth less in Britain for being left hand drive, any US import should be devalued by approximately 10% to acknowledge the power deficit. 5855 were built in total, 1677 of which were to US specification.

Like the 635 upon which it’s based, the cabin is ergonomically very sound – good seats and clear instrumentation make it an easy car to get comfortable with. It’s not noticeably firmer than the base car, though it does feel sharper owing to its larger wheels. It can be upset by mid corner bumps, and the back can be light in the wet but modern tyres have done much to help correct their reputation. But where the M635CSi excels is its performance. As you pass 3000rpm, it feels as if it comes alive, shedding its executive skin in favour of something more sporting. With good steering and an excellent chassis, it’s an absolute riot to drive.

Sills, floors and boot floors are all rust traps, as with the standard 6-series. Likewise, the leading edge of that shark nose bonnet is in the prime position to attract stone chips which can the corrode, leaving an unsightly nose. Metric wheels were standard fitment, with TRX tyres. Many owners have retrofitted imperial wheels from later BMWs – this needn’t necessarily devalue a good car if they’re of a style which suits and remain from within the BMW family. All M635CSis are based on the later 6-series which shared much of its underpinnings with the E28 5-series, better for spares availability than the earlier cars. Check also the timing chain, because in its wisdom BMW specified a simplex chain and when these stretch or snap they can cause untold damage. This was a curious decision given that earlier variants of the engine were fitted with duplex chains. Gearchanges can feel sloppy – it’s a worn shift knuckle and can be rectified. Air conditioning is often fitted but not always functional. An R134a conversion is a good thing – but assume the worst if the owner says it only needs gas. Better to budget for a full system overhaul.

We’d avoid brightly coloured cars and stick to dark metallics and monochrome colours with grey trim. These will be the easiest to resell, and can command a small premium. Cinnabar Red can be a bargain if bought at the right price.

The Jaguar XJ-S V12, or XJR-S, are both clever alternatives to the M635CSi, as is the Audi Quattro if you want something a little more hardcore. The Mercedes 560SEC offers more clout but less dynamism from the chassis, while Porsche’s 944 Turbo is just the ticket for moving those red braces around the country as quickly as possible.