At the Geneva motor show in March 1990, Mercedes-Benz showed the 190 E 2.5-16 Evolution II to the world, the culmination of seven years' work to create the best racing saloon possible. What had begun as the fairly humble (by comparison) 2.3-16v had evolved into a homologation monster, Mercedes desperate to beat the E30 M3 on road and track.
The engine was a work of art, a further refinement of the Evo I 2.5. An even shorter stroke of 82.8mm and a larger bore of 97.3 made it revvier again, howling all the way to 7,700rpm, with lighter con-rods to withstand the speed. In race spec the M102 was making 373hp, and is notable for being the last Mercedes-designed DTM engine - AMG taking the task on after then. In its most successful season, the Evo II racer won 16 out of 24 races - job jobbed.
Which got us thinking. What are the greatest four-cylinder engines ever? We're not going to get any more without forced induction or hybrid assistance, so time for a trip down memory lane for six more to join that incredible Mercedes 2.5 in the hallowed pantheon of four-cylinder greats. Rest assured, keeping it to just the half dozen wasn't easy...
- Honda B18
Where else could we start than with a Honda VTEC? The B-series was notable for being the first Honda engine to use the fabled variable valve timing technology, and that's what gets it in the list. The numbers back then promised much for the future: the 1989 CRX SiR made 162hp from 1,595cc at 7,600rpm, and would go all the way to 8,200.
And the best was yet to come: In B16B form, it powered the first Civic Type R, making a mesmerising 185hp from 1.6 litres - a specific output record at the time. Then the B-series arguably reached its zenith as the B18 that powered the DC2 Integra Type R; for UK-spec cars that meant 190hp at 7,900rpm on the way to a dizzying 8,600 cut-out and a noise to die for. Light, tough, impossibly exciting and also available in a Civic VTI Aerodeck, the Honda B-series is a four-cylinder icon.
- Cosworth BDA
No list like this would be complete without the legendary Belt Driven A Type engine. Devised more than 50 years ago for FIA Group 2 and Group 4 racing in Ford Escorts, the humble Kent block was given dual overhead cams by Cosworth. The engine first appeared in an Escort in 1970, replacing the Lotus Twin cam unit, but nobody could have foreseen the success from then on...
The BDA won rallies, races, and more; it was used to power some truly memorable road cars; it was immensely adaptable - the BD series stretching from 1.1 Formula C spec to Group B engine - and that Cosworth link made it exceptionally cool. But perhaps more than anything else, it was the BDA's sound that secured it hero status. Instantly recognisable for miles down a stage, the combination of low-rev gurgle with a top end shriek has had rally fans bewitched for generations - long may it continue.
- Subaru EJ20
So we've had one Japanese engine in the list, and one with a reputation forged most successfully on the world's rally stages - how about combining the two?
The EJ20 is the storied 2.0-litre boxer four from Subaru; having originally debuted in 125hp, naturally-aspirated form powering a Legacy in 1989, the engine only went out of production this year with the last Final Edition WRX STI made. Over those three decades it's made fans around the globe, the EJ's combination of turbocharged performance, boxer rumble - thank the 1-3-2-4 firing order, too - and motorsport success a pretty formidable combination.
Think, moreover, of the cars powered by an EJ20 over the years, and their legendary status: RB5, P1, STI, GT-B the S20x cars and so on - they wouldn't have been the same without that engine. We could include the 22B as well, though as that used the EJ22G evolution it's probably not quite cricket... And we'll leave the Subaru EJ debate just there, thanks very much!
- Alfa Twin Cam
Another shoo-in for this list, the difficulty really being which motor to select from Alfa's illustrious four-cylinder back catalogue. The twin spark technology actually has its motorsport roots way back in 1914, only then reintroduced to the Twin Cam engine in the 1960s and then as a road car in the 1987 75 2.0 Twin Spark. Later 16-valve four-cylinder Alfas, cars like the 156 and 147, also used Twin Spark badging, but they were Fiat-derived engines with the technology rather than Alfa's own units.
It's that Busso-designed - yes, him again - original that's the real star of the show, the Alfa Twin Cam powering various Spiders, GTVs and Giuliettas for 40 years. Even at launch in 1954 it featured double overhead cams, an aluminium alloy block and a forged steel crank. The Twin Cam's high point, arguably, was in powering the GTA coupes of the late 1960s, making for some of the most memorable road and track Alfas ever made.
- Toyota 4A-GE
Another one from Japan, but then they have shown the world a thing or two about engines over the years. The 4A-GE was another cut from the same cloth: exotic, thrilling and light, yet also tough and immensely dependable. It's those sorts of characteristics that have earned the 4A-GE such a rep over the past four decades.
Introduced in 1983, with development by Yamaha and some inspiration said to come from the BDA, the 4A-GE was another revved little scamp: it would go all the way to 7,600rpm, which was stratospheric back then. Peak power of 130hp was made at 6,600rpm, the little 1.6 fizzing and snarling all the way.
Toyota knew it was on to something good, so dropped the 4A-GE in everywhere: the AE86s, of course, though also the first MR2 and then the later front-drive Corollas. So that's versatility to add to its long list of favourable traits...
- Mercedes-AMG M139
Bringing things right up to date for the four-cylinder superstars is the latest AMG A45 engine. Yes, more than 400hp had been made from 2.0-litres before this M139 - we're looking at you, Evo fans - but never had it been done in such a cohesive and efficient way. You simply wouldn't know such potency lurks under the bonnet of an A-Class, such is the docile and mild-mannered way it can be driven normally.
Go looking for it, however, and there's no doubt about the M139's 421hp potential - it's a monstrous power unit. There's incredible response for something so heavily boosted, a mighty mid-range and the kind of top end enthusiasm that embarrasses rivals. Mercedes made much of the technology that went into the M139, with Nanoslide-coated cylinders, huge 160-bar combustion pressures and a twin-scroll turbo, and the results are mind-blowing. It's undoubtedly a four-cylinder engine we'll be talking about in another 30 years' time.
No, this list is not comprehensive. Yes, we've made some big calls. Tell us why we're wrong below...