Confessions of an Automationeer, Part 13: The Myth of the Straight-Six Supercar

Confessions of an Automationeer, Part 13: The Myth of the Straight-Six Supercar

As described my the previous post, the straight-six engine is making a comeback in the real-life automotive industry after decades of being overshadowed - and replaced - by more compact and supposedly cheaper-to-develop V6 engines. Having described the benefits of inline sixes compared to equivalent V6s, I set myself a challenge involving the use of such an engine, but it wouldn't be for a mass-market volume model. Instead, I would attempt to prove that a supercar or hypercar powered by a straight-six engine could be a competitive offering.

The SMG Hissho: Rolling proof that inline sixes still belong in the engine bays of supercars and hypercars... contrary to popular belief.

To complicate matters even more, I had decided to prioritize light weight and high efficiency over outright performance for this build. Fortunately, the body I chose had excellent aerodynamics, which helped greatly during the engineering phase. The design phase was quite simple, though; I ended up building a car with relatively clean, uncluttered styling in which the side intakes were placed next to the rear window, rather than on the car's flanks. Eventually, I called my car the SMG Hissho LS; Hissho is Japanese for "certain victory" and LS is short for "Lightweight Spec".

500 horses, plenty of torque and not too thirsty for a turbo six... what's not to like about this engine?

The Hissho's turbocharged straight-six had a magnesium block and ran 1.25 bar of boost on premium unleaded. Careful tuning yielded a fairly flat, wide torque curve and 500 horsepower at 7600 rpm, with a redline of 8000 rpm. And with its undersquare dimensions, the engine still weighed less than 200 kilograms even with the turbo hardware included. Having finalized the engine specs, I was now ready to focus on the rest of the car.

In keeping with my aim of making a light car, the body, chassis and wheels were made out of carbon-fiber, while the interior was relatively pared back and covered in lightweight materials. To harness the engine's considerable torque output, the Hissho had an electronically controlled differential, rear spoiler, and dampers. These advanced technologies, combined with the low curb weight of 1.3 metric tons, ensured that the Hissho's dynamics were excellent, with minimal body roll. Moreover, it achieved 30 mpg (US) on the combined cycle - an unusually high figure for a supercar) thanks to careful selection of gear ratios and spacing. And yet, against all odds, at its pre-markup price, it achieved a competitiveness score of over 100 in the two regions in which it could be sold.

Immediately, however, I began wondering how good the Hissho was. As it turned out, I had already built many similar designs to the Hissho over the past few months; this one, though, didn't rely too heavily on quality sliders, as some of those builds did. Even so, I secretly believed that, for a car like this, 500 horsepower wouldn't always be enough. For this reason, shortly before I began work on this economy-oriented build, I decided to take the idea to its logical conclusion. The result was surprising, to say the least.

A concept build of a more extreme six-cylinder hypercar, with ~700 horsepower.

Unlike the Hissho, this earlier build was created with the aim of determining how much power could be squeezed from a straight-six engine given the small engine bay in the body I had chosen. It seemed easier said than done, given the fact that a straight-six is much longer than an equivalent V6, but eventually, I managed to extract a whopping 700 horsepower from a highly undersquare 3.5-liter straight-six. The resulting engine is shown below.

700 bhp from a 3.5L turbo I6? Incredible!

By most objective performance standards the Hissho would have been no match for the bright orange wedge I had made, although the extra torque (and the additional turbo lag that comes with it) made it far less drivable. Nevertheless, it seems fair to consider this test build as a great car in its own right. This is especially apparent when one takes into account the fact that the trim shown here was derived from a less powerful version, aimed at the lower end of the market, but I chose not to show it here because I felt that the Hissho was more deserving of a place on this blog.

That concludes my discussion of straight-six-powered, mid-engined supercar builds, but I won't be done with this engine configuration for some time yet. In the next post, I will explain my plans for the UE4 release of Automation, which is already in open beta.