When four is too few and eight is too many.
The straight-six engine has always been a great choice for the driving connoisseur. While a V8 is where you go for raw power with a rumbling soundtrack and the V6 is for those who want a balance between size and power, the straight-6 offers the smoothest way to deliver plenty of bottom-end torque. That's why BMW has stuck with the straight-6 for so long in its luxury sports sedans and coupes, but it's been against the grain in the face of the more compact V6 that allows easier packaging in an engine bay. Mercedes has thrown its hat back in the ring again recently with the 2019 CLS sedan, and we hope that could mean it's time for a resurgence of the straight-6. We won't be holding our breath though.
Over the decades, there have been some fantastic straight-6 engines from all over the world, not just from the premium German luxury. In fact, our list begins right here in America.
The roots of Jeep's inline 6-cylinder lump that powered the Cherokee and Comanche in the late 1980s, and then the Wrangler and Grand Cherokee in the early 90s, goes all the way back to 1964 and the American Motor Company. Jeep's engine was more powerful than its Japanese V6 contemporaries. It was also relentlessly durable while featuring plenty of torque low down in the RPM range, making it perfect for off-road workhorses. When it was laid to rest in 2006, output had reached 190 horsepower and 235 lb-ft of torque.
A common thread through the rest of this list is reliability. However, the in-house developed TVR straight-6 couldn't be accused of being robust. What you could accuse the TVR Speed Six of being is a brutally thrilling and violent 4.0-liter powerhouse. The only inline-6 that came close to its power at the time was the BMW S54 engine as used in the E46 BMW M3. The M3's powerplant was a technically better-engineered piece of machinery, but anyone that got to drive a Tuscan S, Sagaris, or Typhoon with the 400-horsepower version will likely tell you the Speed Six is the craziest straight-6 they've driven. Right up until it broke, anyway.
Outside of Australia, the Barra family of engines is little known. However, Aussies love their powerful cars and particularly their V8s. The Australian Ford straight-6 made a compelling argument for going without the extra 2 cylinders though. Barra straight-6 engines were muscular and brutish lumps and the 325T lump delivered a turbocharged 420 horsepower from four liters of displacement at the end of its run in the Ford Falcon FPV F6. It's worth noting though that there was a persistent rumor that Ford underquoted the Barra 325T's performance figures in order to not lose sales on the V8 models. Tests have put the engines figures closer to 480 horsepower with that same number for pound-foot of torque.
This was the engine that powered Mercedes across the line to win the 24 Hours of Le Mans and the Carrera Panamericana in 1952. Just to add to its status and ability, it was also used under the hood of the legendary 300SL road car. Part of the reason for its success was the use of Bosch's breakthrough mechanical direct fuel injection system and Mercedes' special aluminum head design. Packaging the long engine was a problem that Mercedes solved by mounting it at a 45-degree angle.
When Toyota first wanted to show the world how well they could build a sports car, they brought in Yamaha to help build the engine. Using the Toyota Crown sedan's inline-6, Yamaha created a double overhead cam cylinder head and bolted on three 2-barreled carburetors. It also made sure the engine didn't redline until 7,000 rpm. Only 350 production versions of the 2000GT the engine went into were made, and existing cars are worth serious money. Using the engine, the 2000GT won the Fuji 1000 Kilometers race in 1962 and set endurance and speed records during a 72-hour test. The car also featured in Sports Car Club of America racing under the direction of Carroll Shelby.
The S54 is the naturally aspirated straight-6 that powered the E46 BMW M3 as well as the Z4 M. It was a 3.2-liter powerplant that developed 333 horsepower, so a little over 100 horses per liter. It was the epitome of what a straight-6 can be in how smooth it was while also delivering a big punch, and the distinctive metal rasp heard through the exhaust only added to its character. The M3 chassis is one of the greatest to hit the road in numbers, but it wouldn't be the icon it still is without that engine.
It's worth noting the N54 engine could also have made the list. It powered a good chunk of BMW's lineup for a long time and was so good that it went into the 1-Series M without an S designation. The beauty of the N54 was how it retains the smoothness of the straight-6 despite its twin turbo set up.
More specifically, we're talking about Nissan's RB26DETT that propelled the R32, R33 and R34 generations of the Skyline GT-R here. The Skyline GT-R is the stuff of legend both in racing and on the public roads. The engine featured a cast-iron block with an aluminum head and a 6 throttle body intake system. The agreement between Japanese manufacturers at the time meant the RB26DETT didn't gain in advertised horsepower over its lifespan, but torque did rise from 260 lb-ft to 289 lb-ft. However, it was reported often that the R34 Skyline was making 400 horsepower on the dyno by the end of its run.
The alphanumeric combination 2JZ became a legend in the late 1990s/early 2000s for car enthusiasts. Even now, many younger enthusiasts are convinced that with a few bolt-on goodies, the twin-turbo 2JZ-GTE will make 1,000 horsepower reliably. That's not quite the case, but there is a reason the engine has become a legend in turbocharged form. Stock, from 1993, the twin-turbo version made 320 horsepower and 315 lb-ft of torque but the key was in the fact the cast iron engine block was as close to indestructible as we've seen yet. That meant building an 11-second Supra was possible by pushing the boost and minimal mechanical modification, and 10-second cars became a common sight at drag strips for those with the know-how and cash to spend.
The M88 has some real pedigree to justify a second BMW entry into the list. It began its life in the ill-fated M1, and was a powerhouse of its time. With a dry sump and double overhead cam, it cranked 272 hp at 6,500 rpm and 243 lb-ft of torque at 5,000 rpm to outpower larger V8's at the time. After the debacle that was the M1, BMW knew the engine was special so they pumped the horsepower up to 282, then dropped it in the 6-Series coupe to create the M635CS in 1983, also known as the M6. In 1985 though, BMW added a couple of doors to the M6 and created an icon in the shape of the first best performing sedan in the world at the time: The first M5.
Jaguar's XK6 engine didn't just power the icon that was the E-Type. In various states of tune, it also powered the C-Type, D-Type, S-Type, XK120, XK140, XK150, the XKSS, and the XJ sedans and coupes. It also won at Le Mans in 1956, 1957, and 1958. The XK6 engine was a work of art that evolved and remained in production from 1949 until 1992. It was built for durability as well as power using a cast iron block and an aluminum head with a seven-bearing crankshaft at its heart.
It was also tunable and garage mechanics and race teams weren't afraid of increasing the compression and adding carburetors. The XK6 engine's durability, tune-ability, it's use in the E-Type, and its triple success at Le Mans marks the XK6 out as an absolute legend.