Summary

From 1980 to 1986, BMW offered a special turbocharged version of its flagship 7-Series sedan called the 745i. The turbocharged six-cylinder engine was supposed to be a more economical substitute for a 4.5-liter V-12 BMW developed in the 1970s, but its fuel consumption was still high, and it performed best at very high speeds. There was also a rare South African version with the normally aspirated (non-turbocharged) 24-valve six-cylinder engine from the M635CSi coupe. The 745i was not officially exported to the U.S. and sold in relatively small numbers. It was discontinued in 1986 and replaced by the 750i and 750iL, which had a non-turbocharged V-12 engine instead of the turbocharged six.

If you’ve looked at a BMW brochure in the past decade, you’ve probably noticed that most of the company’s offerings are now turbocharged. That wasn’t always the case: When the twin-turbo E92 335i was launched back in 2006, BMW hadn’t offered a forced-induction gasoline engine in 20 years. The company’s previous stab at spark injection turbocharging had been the E23 745i, a less-than-successful attempt to beat Mercedes-Benz at its own game.

(Author’s Note: An earlier version of this article appeared in Autoweek magazine in 2013. It has been extensively revised and greatly expanded for Ate Up With Motor.)

(Photo copyright © 2024 Gregory Mazur; used with permission)

From V-12 to Turbo Six

Announced at the Frankfurt International Auto Exhibition (IAA) in September 1979 and launched in mid-1980, the first BMW 745i was the flagship of the then-three-year-old E23 7-Series line, intended to challenge the Mercedes-Benz eight-cylinder S-Class sedan on its own terms.

At the insistence of BMW CEO Eberhard von Kuenheim, BMW had been trying for years to elbow its way into Mercedes territory, but the Bavarian firm had lacked an engine capable of matching the bigger Mercedes V-8s. The 745i promised to change all that, with a turbocharged six that outmatched the most powerful version of the latest W126 Mercedes-Benz S-Class, 252 PS DIN to 240 (185 kW to 177).

The impact of its announcement was somewhat undercut, however, by the awareness that the new flagship’s Turbomotor was really something of a consolation prize, a last-minute stand-in for the 4.5-liter V-12 BMW had originally wanted to build.

Even before returning to the six-cylinder market back in 1968, BMW had been contemplating once again offering engines with more than six cylinders, although it wasn’t until 1979 that officials publicly acknowledged those efforts, perhaps mindful that the previous BMW V-8 (offered from 1954 to 1965) had contributed to the company’s brush with bankruptcy in the early sixties. After exploring the possibility of a new V-8 engine, BMW had opted for a 60-degree V-12 based on the company’s latest M20 six. Despite some exotic features, like dry sump lubrication and Bosch digital Motronic engine controls integrating electronic ignition and L-Jetronic electronic fuel injection, the V-12 had extensive commonality with the small six while offering greater smoothness, prestige, and power: 272 PS DIN (200 kW) and 269 lb-ft (365 N-m) of torque from 4,463 cc (272 cu. in.). The V-12 promised to rival even the vaunted W116 Mercedes-Benz 450SEL 6.9 in acceleration, if not in top speed.

The V-12’s downfall was fuel consumption, which was very heavy by European standards — a meager 16.8 mpg (14.0 L/100 km) DIN “normal consumption” — and flew in the face of the new U.S. Corporate Average Fuel Economy (CAFE) standards. The BMW management board had finally hedged, shelving the V-12 project in 1977.

Its demise left the BMW flagship sedan without a flagship engine. At launch, the top of the new E23 7-Series line was the 733i, with a 3,210 cc (195.9 cu. in.) six making 197 PS (145 kW) in European trim. Compared to the slightly cheaper eight-cylinder 350SE of the W116 Mercedes S-Class, the 733i had a slight edge in acceleration, but not in smoothness or refinement. The German car magazine auto motor und sport (AMS) found the BMW second-best in that league, and BMW had nothing to challenge the pricier 450SEL or 450SEL 6.9. Even the subsequent introduction of the more powerful 735i, with a 3,453 cc (210.7 cu. in.) six offering 218 PS (160 kW), wouldn’t be enough to directly match V-8 rivals.

One possible alternative — and one that would resurface later — was the hot DOHC 24-valve M88 six from the new M1 coupe. This was a good deal more powerful than the SOHC sixes, but it was also a peakier, noisier engine, not really appropriate for the senior executive class, and it was also rather expensive to build.

Much like their counterparts at Buick during the same period, the engineers in Munich turned instead to turbocharging the “big” M30 six, which promised to combine V-8 power with six-cylinder fuel economy and emissions. This was not entirely new territory, since BMW had been building turbocharged racing engines since 1969, but the company’s only previous turbocharged production car had been the short-lived 2002 Turbo in 1973–1974, which was a high-performance homologation model, not a flagship Autobahnkreuzer aimed at the senior S-Class Mercedes.

(Interestingly, while BMW management decided to develop diesel engines at the same time the V-12 was canceled, the company’s first M105 turbodiesel engine, a 2,443 cc (149.1 cu. in.) six produced by a joint venture between BMW and Steyr-Daimler-Puch, wouldn’t arrive until the 1983 model year, three years after the turbocharged petrol six.)

M102 Turbo Engine

Despite the suggestive badge, the turbocharged M102 engine of the initial 745i actually displaced 3,210 cc (195.9 cu. in.), just like the M30B32 six from the cheaper normally aspirated 733i and 732i. BMW justified the loftier badge based on the Fédération Internationale de l’Automobile (FIA) equivalency factor for turbocharged engine, which at that time was 1.4:1, meaning that a turbocharged 3,210 cc engine was considered to have an equivalent displacement of 4,494 cc (274.2 cu. in.) for classification purposes. At the time, this prompted a certain amount of eye-rolling from the automotive press, but it was at least more grounded than modern BMW practice, where model identification numbers that once indicated engine displacement in deciliters have become increasingly arbitrary.

To prepare it for turbocharging, the 3.2-liter six was modified with stronger connecting rod bearings, Nimonic alloy exhaust valves, and a new exhaust system. As with the normally aspirated engine, fuel delivery was by Bosch L-Jetronic electronic fuel injection. Unlike the canceled V-12, the M102 engine did not use the new Bosch Motronic integrated digital engine computer, a curious choice that to us suggests a rather short development timetable.

Boost came from a single air- and oil-cooled KKK K27 turbocharger, made by Frankenthal-based Kühnle, Kopp & Kausch (now owned by BorgWarner), which also made the turbochargers used by the Porsche 924 Turbo and Porsche 930. Maximum boost was set at 0.6 bar (8.7 psi), although BMW said peak power was achieved with slightly lower 0.5 bar (7.3 psi) boost, in the interests of better fuel economy.

Unlike the contemporary Buick 3.8-liter (231 cu. in.) turbo V-6 or the Saab Automatic Performance Control (APC) system, the M102 engine did not have knock sensors, but it did have an air-to-air intercooler to reduce the temperature of the compressed intake charge by up to 104 degrees Fahrenheit (40 degrees Celsius) before it reached the intake manifold. (Since the M102 six had L-Jetronic injection, the manifold was “dry,” with fuel injected at the intake ports.) As a further safeguard against detonation under boost, the engine’s compression ratio was reduced significantly — initially to 7.0:1, compared to 9.3:1 for the normally aspirated engine.

As with the old Oldsmobile F-85 Jetfire engine, the turbocharger controls were designed to reach maximum boost early (from as little as 2,500 rpm) and maintain peak torque output, rated at 280 lb-ft (380 N-m), through much of the rev range, up to 4,800 rpm. The redline was 6,300 rpm, but peak power — rated at 252 PS (185 kW), 20 PS (15 kW) less than the stillborn V-12 — was achieved at 5,200 rpm.

The M102 had two pressure-controlled bypass valves. A conventional wastegate opened if intake manifold pressure exceeded 0.6 bar (8.7 psi), limiting boost by allowing some exhaust gas to bypass the turbocharger. There was also an overrun control valve, which BMW called the Umluftventil, or return air valve, that opened in response to manifold vacuum, allowing some of the compressed and cooled intake air to flow from the intake pipe back into the turbocharger’s compressor inlet. Its purpose was to keep turbine speed from dropping abruptly if the driver lifted off the accelerator.

A Heavy-Drinking BMW Flagship

BMW was keen to emphasize that the turbocharged 745i was an executive car, not a sport sedan. There were no hood scoops, cooling vents, racing stripes, call-out decals, or special instruments (to the annoyance of some critics, who wanted a boost gauge). Although there was an available sport suspension with a hydro-pneumatic self-leveling system, low-profile Michelin TRX tires, and metric alloy wheels, it was initially an optional extra. Standard 745i fare was the same relatively soft suspension and 205/70VR14 tires as other 7-Series cars, although 745i did come standard with a Bosch four-channel antilock braking system (ABS), a new addition to the 7-Series line.

Another telling point was that the 745i turbo was available only with automatic, initially the ZF 3HP22, a three-speed Simpson gearset transmission optional on other 7-Series models. BMW built a handful of pilot production turbo cars with five-speed manual gearboxes, but that option was never offered in production. The company offered several rationalizations for standardizing the automatic — its torque converter helped to compensate for the turbocharged engine’s weaker torque between idle and the arrival of boost, and power-shifting a relatively wide-ratio automatic kept the turbo on the boil through the rev range — but we assume the principal reason for not offering a five-speed was that it would have risked sending the wrong message about the car’s intended mission.

To some, standardizing the automatic suggested an interest in adapting the 745i for American sales, but while BMW said the turbocharger arrangement was compatible with three-way catalytic converters and lambda feedback control, the E23 745i was never officially certified for U.S. sales (and was never offered with a catalytic converter even in Germany). Nonetheless, there were some gray-market importers, who combined the turbo package with the emissions equipment from the U.S. 733i, reducing output by about 20 horsepower (15 kW) and creating some uncomfortable ambiguities with regard to warranty coverage; BMW was reluctant to accept responsibility for gray-market cars. The E23 745i would also be a rare sight in the UK and Australia, since the turbocharger and its bulky intercooler installation precluded right-hand-drive (RHD) conversion.

In any case, the turbocharger package was really optimized for the unrestricted Autobahn. Until the tachometer needle approached 3,000 rpm, the 745i was actually a bit sluggish compared to a normally aspirated 732i or 735i, and it was hampered by the transmission’s reluctance to downshift at part-throttle. BMW claimed 0–62 mph (0–100 km/h) in 7.8 seconds, which was good but hardly spectacular for the era (and 0.4 seconds slower than the abortive V-12 car). Once the tachometer needle crossed 3,000 rpm, however, the 745i would soon leave its normally aspirated brethren for dead: From 62 mph (100 km/h), the 745i would reach 112 mph (180 km/h) more than 10 seconds quicker than a 735i Automatic. Manually holding second gear as long as possible also gave the 745i an edge in highway passing over the latest W126 Mercedes-Benz 500SE, which had the advantage at lower speeds. The BMW turbo couldn’t match the top speed of the taller-geared Mercedes, which in AMS tests topped out at 144 mph (232 km/h) to the Bavarian car’s 140 mph (226 km/h), although the latter was still 2 mph (4 km/h) faster than the BMW factory claim.

This impressive high-speed performance had its costs. The first and most obvious was fuel consumption: Even on paper, the M102 engine was only marginally more economical than the 4.5-liter V-12, with DIN normal consumption of 17.4 mpg (13.5 L/100 km) against the 12-cylinder engine’s 16.8 mpg (14.0 L/100 km). In the real world, it was easy to push fuel economy below 12 mpg (20 L/100 km), closer to a 5.3-liter (326 cu. in.) Jaguar XJ-12 than a normally aspirated 7-Series. The first AMS full road test of the 745i returned a grim overall test average of 10.9 mpg (21.6 L/100 km) on German low-lead premium fuel, dipping to a mere 10.4 mpg (22.5 L/100 km) in 100 mph (160 km/h) Autobahn cruising, and as low as 8.9 mpg (26.5 L/100 km) with a lot of full-throttle acceleration. By comparison, the taller-geared, significantly more aerodynamic Mercedes 500SE managed a comparatively thrifty 13.1 mpg (17.9 L/100 km) on the Autobahn, although the 500SE was a bit thirstier than the 745i in urban driving. Tellingly, BMW increased the size of the turbocharged car’s fuel tank from 23 to 27 U.S. gallons (85 to 100 liters) to compensate for its thirst.

One could argue that fuel consumption was a trivial point for the intended clientele of these relatively rare and very expensive cars. At launch in June 1980, base price of the 745i in West Germany was DM 54,200, 8,600 marks more than the 735i and 73 marks more than a Mercedes 500SE. The 745i was not quite as audaciously priced as it appeared at first blush, thanks in large part to its standard antilock brakes (ABS was an extra DM 2,370 on other 7-Series models, and around 2,500 marks on the Mercedes S-Class), but this was still a costly prestige model intended to compete in the upper tiers of the European executive market. On the other hand, given that fuel consumption had been the principal reason for dropping the V-12 in favor of the turbo six, the fact that the turbocharged M102 engine was thirstier than a 4,973 cc (303.4 cu. in.) V-8 was none too impressive, and the Mercedes M117 V-8 was both more flexible and more refined than the BMW M102 six.

The turbocharged engine brought some other compromises as well. Much as it relished Autobahn speeds, the M102-powered 745i wasn’t much for slowing down: The overrun recirculation valve effectively eliminated engine braking, so lifting off the throttle at speed gave a disorienting sense of uninterrupted momentum. ABS improved braking control, but not swept area or brake cooling, which were no different than on lesser 7-Series models, and could be overtaxed with the higher velocities on offer.

As for handling, BMW in the early eighties still clung to MacPherson struts in front (with the company’s novel double-pivot lateral links, giving a dynamically variable scrub radius) and semi-trailing arms in back. Steering was more precise and handling more neutral than was customary for luxury sedans of this era, but the 20-degree semi-trailing arms made it easy to bring the tail out with the throttle, either by applying too much power when existing a turn, by lifting off the accelerator after entering too fast, or by triggering a mid-corner automatic downshift. Contemporary attitudes about this behavior were mixed: American drivers who fancied themselves highly skilled found it delightful, since it was flattering if properly managed, while British testers, faced with generally higher speeds on narrower, wetter roads, regarded it as worryingly skittish; German reviewers tended to fall somewhere between these extremes. There was little serious debate, however, that the penchant for tail-happiness could get an unprepared or unwary driver into a lot of trouble.

Some testers, like Paul Frère, felt the early 745i was less prone to trailing throttle oversteer than its naturally aspirated relatives, since the overrun air return valve blunted the torque reaction that would otherwise be caused by lifting off the accelerator. However, semi-trailing arm suspensions did not suffer nonlinear power delivery gladly, and the transition from off-boost to on-boost power could make the turbocharged car a handful, especially in the wet. The Swiss magazine Automobil-Revue (AR) found that the presence or lack of a limited-slip differential made a significant difference; with an open differential, a sudden kickdown was more likely to set the inside rear wheel spinning than kick the tail out, but the opposite was true with limited-slip. The sport suspension and TRX package offered on the 745i didn’t change the car’s basic dynamics, but they did usefully expand the limits of adhesion and made the rear end’s sideways-seeking tendencies easier to manage short of the limit.

Ride was not the E23’s strongest suit, in any case. Even with the softer standard suspension, it wasn’t terribly absorbent at around-town speeds, and some testers felt it was under-damped at higher speeds. The TRX package had better high-speed damping, but was even stiffer than the standard setup at low speeds. AMS was also none too keen on the front seats for longer drives, although their testers thought the 7-Series had a more comfortable back seat than did the contemporary S-Class. Wind noise was another sour point, a sign of an aging platform for which aerodynamics had ranked relatively low on the original list of design priorities.

In sum, the 745i was a narrowly focused car, aimed at the kind of well-heeled, aggressive driver who would weigh the fuel costs of a road trip against the price of an airline ticket rather than the fuel economy of some milder sedan; who was more concerned with maintaining high trip average speeds than with wind noise or around-town ride comfort; and who might actually learn to program the car’s complicated trip computer, a standard 745i feature optional on other senior BMW models. The turbocharged 745i wasn’t really an all-arounder like the senior S-Class models, and it didn’t do much to challenge Mercedes leadership in this class, in either sales volume or prestige.

Improvements

To their credit, BMW engineers were obviously aware of the limitations of both the E23 7-Series generally and the 745i in particular, and mitigation was not long in coming. At the 1981 Frankfurt show, less than a year and a half after launch, the company announced that the turbocharged engine had received a variety of detail changes aimed at improving fuel economy, in particular a half-point higher compression ratio (7.5 rather than 7.0:1).

These refinements reduced fuel consumption by about 10 percent, although the results were not so much “more economical” as “incrementally less profligate.” AMS reported a test average of 12.0 mpg (19.5 km/L) with the latest 745i, which was still harrowing by European standards. Their test of a 1982 Mercedes-Benz 500SEL, which also incorporated various changes aimed at reducing fuel consumption (known in Stuttgart as the Energiekonzept, or “Energy Concept”), managed 20.1 mpg (11.7 L/100 km) overall, although the Mercedes sacrificed a bit of power and some acceleration in the process.

Although BMW reported no changes to the power or torque output of the revised M102 engine, the more economical 745i was also quicker than before: 0–62 mph (0–100 km/h) in as little as 7.2 seconds and 0–100 mph (0–160 km/h) in 17.4 seconds, again per AMS. Taking full advantage of this extra performance required manually holding the automatic’s lower gears, which was not ideal (the transmission didn’t always respond swiftly to manual selections, which risked encountering the injection system’s 6,300 rpm fuel cutoff), but it gave the 745i impressive performance for 1982.

These improvements, alas, were not free. Base price of the 745i had risen to DM 56,150, and a limited-slip differential, which had initially been standard on West German cars, was now an extra 683 marks. Adding the TRX package (DM 1,281), sunroof, power seats, metallic paint, headlamp washer system, and newly available cruise control brought the price to a hefty DM 63,738, enough at that time to buy a 323i sedan and a 520i. Even this price did not include air conditioning, which was rarely standard on European executive cars of this era. Automatic climate-controlled air conditioning had been optional on the 745i since launch — for an extra 3,830 marks, thank you very much — but by 1982, there was also a conventional manual system, offered for a mere DM 3,215.

Despite the turbocharged 7er’s high price and unseemly drinking problem, BMW had built 6,193 turbocharged 745i sedans by the end of 1982, a modest but respectable total obviously constrained by the lack of North American or RHD exports. By comparison, Mercedes-Benz built 29,234 500SE and 500SEL sedans in the same period, although the Mercedes was much more widely available.

The lack of a RHD 745i was especially galling for BMW South Africa, which in this era was doing good business selling locally assembled 7-Series sedans to some of that nation’s worst people. The E23 7-Series was then a favorite choice of senior officials of South Africa’s apartheid government, including prime minister P.W. Botha, whom The Guardian later described as “one of the most evil men of the 20th century” (a ranking with much stiff competition, to be sure). Rather than deprive these worthies of the opportunity to own the company’s flagship model, BMW South Africa contrived its own locally built and engineered RHD 745i, powered not by a turbocharged engine, but rather by the latest M88/3 version of the DOHC 24-valve engine from the BMW M1, the same version subsequently used in the M5 sedan and E24 M635CSi coupe. (There was no attempt to rationalize the “745i” badge, which was probably just as well.)

With 290 hp DIN (213 kW) and an available five-speed gearbox (although many likely had the optional ZF 4HP22 automatic), the South African 745i was faster than the turbocharged car — the factory claimed 0–100 km/h (0–62 mph) in 7.0 seconds and a top speed of 240 km/h (149 mph) — and somewhat harder-edged. With a lofty price tag of 65,000 rand plus VAT — then the equivalent of around DM 150,000 in West Germany, although many features that were optional in Germany were standard fit on the South African cars, including automatic air conditioning — the 24-valve 745i was strictly for the few, and, presumably, the white. (AMS, in an embarrassing example of the cultural insensitivity that too often characterizes buff books, pictured the South African 745i with a Black chauffeur behind the wheel while wondering longingly whether such a car might eventually be available in Germany.) Production was very limited, amounting to no more than 209 cars between 1983 and 1986.

A Facelift and the M106 Turbo Engine

For 1983, BMW gave the entire E23 line another round of significant revisions intended to keep the 7-Series viable until its replacement, which wouldn’t be for at least three more years. The 7er had actually gone through a weight-reduction program shortly before the 745i debuted; the latest changes trimmed a bit more weight while tidying up the dated aerodynamics with a lower grille and ugly black filler panels in the A-pillars. This improved the drag coefficient from 0.44 to a still-lackluster 0.41, which was as much as the BMW board deemed they could afford on a flagship model whose basic tooling and development costs hadn’t yet been fully amortized.

From a driver’s standpoint, a more worthwhile change was a revised rear suspension with the semi-trailing arms angled at 13 rather than 20 degrees, which, combined with a stiffer front anti-roll bar, promised to reduce acceleration squat, camber change, and the propensity for hanging out the tail on a trailing throttle. This it did, although the difference was one of degree rather than general trajectory, particularly on wet or slippery roads.

Across most of the line, the three-speed ZF 3HP22 automatic was also replaced by the four-speed 4HP22, with a lockup torque converter, 0.73:1 overdrive top gear, and an array of different automatic and manual modes. It was electronically controlled and integrated with the Bosch Motronic system, which automatically retarded the spark timing during gear changes for greater smoothness.

This new transmission became standard on the updated 745i, which arrived in mid-1983, sporting not only the new automatic, but also a new turbocharged engine, designated M106. The M106 was based on the M30B34 engine in the 735i and displaced the same 3,430 cc (209.3 cu. in.). (Had BMW been serious about the FIA equivalency factor, the new engine would have been considered the equivalent of 4,802 cc (293.0 cu. in.), making the car a 748i, but the “745i” designation remained.)

The M106 had higher compression, now 8.0 rather than 7.5:1, and a Bosch Motronic II digital engine computer rather than the simpler L-Jetronic system of the M102. On the M106 engine, the Motronic system managed boost pressure as well as fuel delivery and ignition timing, taking input from two knock sensors in the cylinder head and from pressure sensors in the compressor outlet and the intake manifold aft of the throttle butterfly. The previous return air system was deleted, and the Motronic system now managed the wastegate to control boost pressure based on a series of preprogrammed digital maps. Knock was controlled by retarding the ignition timing, opening the wastegate valve to reduce boost, or both.

We were unable to obtain copies of contemporary German technical papers describing the new boost control system in detail, and the BMW press kit’s technical description is vague on several points, but it appears that the M106 had a more effective intercooler — it was now said to reduce charge temperature by up to 131 degrees rather than 104 degrees Fahrenheit (55 rather than 40 degrees Celsius) — and that peak boost pressure was functionally lower than before; peak turbine speed was said to have been reduced by over 30,000 rpm. This allowed leaner mixture settings and more spark advance for better fuel economy, but meant that the M106 was no more powerful than the M102 despite its higher compression and larger displacement. BMW claimed the same 252 PS (185 kW) and 280 lb-ft (380 N-m) of torque as before, albeit at slightly lower RPM (now 4,900 and 2,200 rpm respectively).

Since the new 745i was about 80 lb (37 kg) lighter than before and had greater low-end torque, one might expect it to be quicker than its predecessor, but even BMW admitted it was not. The factory now claimed 0–62 mph (0–100 km/h) in 7.9 seconds and the standing kilometer (0.63 miles) in 28.2 seconds, compared to 7.8 and 28.3 seconds, respectively, for the original low-compression M102 car. An early AMS test car with the new engine could manage no better than 0–62 mph (0–100 km/h) in 8.7 seconds and the standing kilometer in 29.2 seconds, due mainly to traction problems that made it difficult to get a good launch; the 3.4-liter car took 1.3 seconds longer than its predecessor to reach 37 mph (60 km/h) and couldn’t make up the difference at higher speeds. Cars tested by both AMS and AR a year or so later did better, managing to equal or better the factory acceleration claims, but this only underscored the fact that there had not been any progress in this area since 1980. The second AMS test car did beat the factory’s claimed 141 mph (227 km/h) top speed, reaching nearly 144 mph (231 km/h), an achievement that probably reflected the lower numerical axle ratio (reduced on four-speed cars from 3.07 to 2.93:1) and slightly lower drag.

The more immediate point of the exercise was to reduce fuel consumption by a further 9 percent, making the latest 745i nearly 20 percent more efficient than the original edition. It still wasn’t very good in absolute terms — between 13.4 and 14.1 mpg (16.7 to 17.5 L/100 km) overall in AMS and Automobil-Revue tests — and it was still worse than the 500SE. Moreover, achieving even these unimpressive figures required enduring the finicky behavior of the 4HP22 transmission’s Economy mode, in which the automatic was reluctant to downshift without a full-throttle kickdown and tended to hunt annoyingly between third and fourth. The overdrive fourth gear was also of little help at higher Autobahn speeds; top speed had to be achieved in third because the transmission would not stay in fourth gear at full throttle even if a 4–3 downshift risked hitting the fuel cutoff.

In other respects, the latest 745i was a cautious step forward. A rear anti-roll bar and hydro-pneumatic self-leveling struts were now standard, and the 13-degree semi-trailing arms reduced the likelihood of kicking the tail out abruptly when the boost came on. Wind noise was better muffled, and eliminating the return air valve served to mitigate the earlier car’s vertiginous lack of engine braking.

“Vertiginous” was nonetheless an apt word for the escalation of the 745i sedan’s base price, which rose from DM 63,204 in mid-1983 to DM 65,700 by January 1984; by the end of the line in mid-1986, it was a lofty DM 73,100. From 1984, there was a new 745i Executive trim level, with additional standard equipment, walnut wood trim, and buffalo leather upholstery. This started at DM 83,760 in 1984, rising to 90,900 in 1985, when it was joined by an even pricier Highline grade that slathered the cabin in soft Nappa leather. In factory list price terms, the 745i Highline was the second-most expensive contemporary BMW model (after the M635CSi coupe), starting at DM 94,350 in 1985 and DM 96,750 in 1986. Although that was enough to buy three E30 320i sedans, these prices still didn’t include air conditioning, which could push the retail price above 100,000 marks.

(Author’s Note: If you’d like to get an approximate sense of what these West German prices represented in contemporary U.S. dollars, Werner Antweiler of the University of British Columbia Sauder School of Business maintains a Pacific Exchange Rate Service that has tables of historical exchange rates for different currencies from 1950 on, based on International Monetary Fund data. Because the relative value of the Deutschmark fluctuated so much during this period (the rates presented for 1972 on are annual averages) and didn’t necessarily have any direct relationship to the prices of German products sold in other markets, actual conversion is left as an exercise for the interested reader.)

Nonetheless, the 745i continued to sell about as well as before. BMW production figures are by calendar year rather than model year, so the 1983 figures don’t distinguish the late M102 and early M106 cars, but total 1983 to 1986 production was 9,838, which includes the South African 24-valve cars. Mercedes-Benz W126 500SE and 500SEL sedan production for the same period totaled 60,167, plus a further 18,696 560SEL sedans built in 1985 and 1986. Grand total for E23 745i production, including pilot production cars built in 1979, was 16,031 units.

V-12 Return

Neither the turbocharged six nor the twin-cam M88 engine would return for the subsequent E32 7-Series line, as BMW began having second thoughts about the 745i even before the introduction of the M106 engine. The turbo six had been expedient and cheaper to build than a V-12 (although that wasn’t necessarily something one wanted to brag about in this rarefied class), but its fuel economy benefits had proven more notional than practical, and had come with too many compromises. It had developed a certain following — the 745i accounted for about 5.6 percent of all 1977–1986 E23 7-Series production, a respectable fraction, all things considered — but it appealed most strongly to a particular subset of existing BMW fans, which we suspect was simply not enough, given Von Kuenheim’s preoccupation with matching Mercedes-Benz.

In early December 1982, BMW engineers began serious work on a new V-12 engine. Development proceeded rapidly and in great secrecy: The design was mostly finalized by June 1983, and the first prototype engines were running on test stands that October. Dubbed M70, the new V-12 was based on the architecture of the latest M20B25 small six (although the commonality was primarily in production tooling and transfer equipment rather than in actual parts), but the block was aluminum rather than cast iron, keeping dry weight to 529 lb (240 kg), some 77 lb (35 kg) lighter than the stillborn 4.5-liter V-12, but only a few pounds lighter than a cast iron Chevrolet V-8. Many of the V-12’s components were identical between both banks, with each bank having its own distributor and Bosch Motronic injection system, which was obviously more expensive on a unit basis, but helped to reduce tooling costs. Like contemporary BMW small sixes, the M70 had single overhead camshafts (chain- rather than belt-driven) and only two valves per cylinder.

The M70 shared the M20B25 six’s bore and stroke, giving a total displacement of 4,988 cc (304.4 cu. in.). While the original goal was to match the stillborn 4.5-liter’s 272 PS (200 kW), the production M70 bettered its predecessor’s output by 10 percent, giving 300 PS (220 kW, 296 SAE net horsepower). Unlike the M102 and M106 engines, even the West German version had three-way catalytic converters with oxygen sensor feedback control. In the E32 7-Series, linked to a four-speed ZF 4HP24 automatic (the sole transmission offered), the V-12’s DIN standard fuel consumption was up to 25 percent higher than the M106-powered E23 745i, but BMW claimed that the short-wheelbase E32 750i was a half-second quicker to 62 mph (100 km/h) and 0.9 seconds quicker through the standing kilometer, with a much higher (and electronically limited) top speed of 155 mph (250 km/h). The first AMS full test of the long-wheelbase 750iL returned 15.2 mpg (15.5 L/100 km) overall, significantly better than the old 745i had ever managed, and on regular unleaded gasoline rather than leaded Super.

More importantly, the M70 finally allowed BMW to offer something on its senior models that Mercedes-Benz couldn’t yet match. The latest W126 560SEL had more displacement — 5,547 cc (338.4 cu. in.) — and nearly as much power (although the 5.6-liter Mercedes engine could only match the 300 PS (220 kW) of the BMW V-12 without catalytic converters — but the first Mercedes V-12 engine wouldn’t arrive until 1991, a small but no doubt satisfying moral victory in the ongoing war between Munich and Stuttgart. Moreover, the V-12 cars’ power and snob appeal could be appreciated even by customers who would never exceed 70 mph (112 km/h), and since they posed fewer packaging problems and were catalyzed even in West Germany, they could be certified for U.S. sale without undue difficulty.

In a 1987 CAR comparison of ultra-high-end sedans, the acerbically erudite LJK Setright dismissed the 750iL as inferior to the 735i, “neither quieter nor sweeter … nothing more than a badge of rank among those for whom promotion is essentially stipendiary.” Nevertheless, the E32 750i and 750iL were far more commercially successful than the old 745i, accounting for 48,559 units through 1994 — 15.6 percent of E32 7-Series production. The V-12 returned for the E38 generation, now bored and stroked to 5,379 cc (328.2 cu. in.), becoming the M73. For the stylistically unfortunate E65 7-Series in 2002, BMW replaced the SOHC M73 with the all-new N73, this time a DOHC 48-valve engine displacing 5,972 cc (364.4 cu. in.).

Although most BMW diesel engines had long been turbocharged, BMW didn’t return to petrol turbocharging until 2006, beginning with the twin-turbo N54 six, first introduced in the E92 335i. Turbocharged engines were initially offered on the performance ends of the range, and gradually spread to include less-racy models. For the F01 7-Series in 2008, BMW followed the lead of Mercedes-Benz in turbocharging its latest V-12, dubbed N74, which now had twin Garrett turbos and 544 PS (400 kW). This engine returned for the subsequent G11, initially producing a whopping 610 PS DIN (449 kW) — over twice the output of the original normally aspirated M70. (A version of this engine remains in production for Rolls-Royce, although BMW finally dropped its own V-12 models in 2022.) The modern BMW lineup has become increasingly turbo-heavy, with the battery electric models now the sole exceptions.

Today, more than 40 years on from the turbocharging renaissance that spawned the E23 745i, the technology has finally matured enough to pay off the promise suggested back then. With the addition of variable valve timing, direct injection, and more sophisticated engine controls, it’s now possible to produce tractable and relatively economical turbocharged street engines offering 100 or more horsepower per liter. This has made engine displacement a matter of diminishing importance, not least in the relationship between model designation and actual engine size. (Current BMW petrol models identified as “-30i” generally have 2-liter (121.9 cu. in.) turbo fours.)

BMW could have been ahead of the curve had they continued developing the turbo package beyond the M106 engine (which had made some useful strides in practicality), but it’s clear that the 745i was always more about corporate ego than efficiency or mechanical progress. With the advent of the V-12 750i, BMW finally had the prestige engine they’d wanted in the first place, and it sold well enough to make it seem like they had missed a bet with the E23. (The fact that the company clung to its 12-cylinder engines as long as it did is strong evidence that the snob appeal was not solely for the punters.)

Born of second-guessing, the E23 745i represented not so much a prelude of things to come as a novel example of a kind of car BMW doesn’t really make anymore: rare, eccentric, flawed, and as specialized as it was swift. It was not a car designed for mass appeal — even most 7-Series buyers of the time would have been happier with a 735i (particularly on U.S. roads) — but for those few who saw the point, the eccentricity was part of the trip.

NOTES ON SOURCES

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