These three modern inline-sixes are keeping the layout alive
The inline-six engine was the go-to engine for years across many manufacturers before the V design took over every market from the luxury sector down. The humble inline-six was relegated to workhorse applications and faded from popularity. However, in recent years the design has seen a resurgence, and this year three inline-six engines from three different manufacturers were included on the Ward’s 10 Best Engines list. What does this design have that others don’t? Jason Fenske of Engineering Explained lays it all out in his latest video.
The three engines discussed are from BMW (B58), Mercedes-Benz, and GMC (Duramax). Each has features that make them unique, but they all share a few key components: the inline-six layout (duh), turbocharging, and the use of air-to-water intercoolers. The Chevrolet is the only diesel engine discussed.
The BMW engine discussed is the B58 found in the 2020 BMW Z4 and Toyota Supra. The integrated turbocharger housing combines with the use of the Valvetronic system to keep the intake pressurized and controls air into the combustion chamber by varying the lift of the intake valve. The arrangement helps keep pumping loss and turbo lag to a minimum, creating a more efficient and responsive package.
Even with all that going on in the BMW engine, the Mercedes motor is the most complicated of the three. It uses an integrated start-generator to provide electric boost at low rpm, which can add up to 184 pound-feet of torque. The engine also includes an electric supercharger to augment the turbocharger. Capable of 6 psi of boost, that electric supercharger helps eliminate turbo lag by pressurizing the intake and helping spool the turbo.
The most straightforward engine, in contrast, is the GMC diesel. The Duramax uses a standard 15:1 compression ratio to provide compression ignition, but one of the things that stood out to Fenske when researching the engine was the massive fuel pressure—over 36,000 psi. This is seven times higher than the BMW’s, and for good reason. The higher pressure allows the use of smaller nozzles in the fuel injector to create a finer mist. That finer mist ignites and burns better, increasing both efficiency and power.
These three engines represent only 30 percent of Ward’s top ten list, but we are just happy to see the inline-six coming back. Is this your favorite engine layout or do you prefer a different arrangement or cylinder count? Tell us in the comments below.