6 Reasons Porsche Uses Flat-Sixes (And 4 Reasons BMW Uses Inline-Sixes)May 19, 2020
Porsche and BMW are two German automotive manufacturers that routinely push the entire industry forward with technology innovations that improve performance in their vehicles. They’re also two companies that are largely connecting to an iconic engine layout, as Porsche has employed a flat-six since the 911’s introduction back in 1963 and BMW has built the inline-six for which it is famous since 1977.
Porsche’s flat-sixes have undergone radical changes over the years. Where early 911 variants started out with a 2.0-liter powerplant producing only 130 horsepower, today’s beastly GT2 RS displaces nearly as many liters and employs a twin-turbocharger setup to produce 700 horses.
BMW, meanwhile, has had an on-again-off-again relationship with the inline-six in its highest-performance cars, like the iconic M3. Today, the M3 once again has an inline-six, though it, too, has received forced induction to keep up with the competition.
As the automotive industry has evolved over the years, why have Porsche and BMW remained so committed to their long-tenured engine designs? Here are seven reasons Porsche uses flat-sixes and four reasons BMW uses inline-sixes.
11 Porsche’s Flat-Six: Low Center Of Gravity
Probably the main reason Porsche uses flat-sixes to this day is because the layout allows for a low center of gravity, which is an essential feature in sports cars. And this becomes even more of a concern given that Porsche’s flagship model, the 911, still hangs its powerplant out behind the rear axle—a low center of gravity helps the feeling of a 911 “squatting” during cornering, rather than fishtailing disastrously.
10 Porsche’s Flat-Six: Opposing Pistons
One of the main mechanical advantages of the flat-six engine is that three pistons on one side move directly in the opposite direction from those in the other bank of three. This means that the engine’s forces are more evenly balanced, which translates to less of a need for counterbalancing, aggressive mounting or bracing, and fewer moving parts—all of which are good things to avoid when it comes to engine development.
9 Porsche’s Flat-Six: Lightweight
Having fewer parts and better orientation of opposing forces means that Porsche can reduce the number of parts in the flat-six engine, which thereby reduces overall weight. And of all the automotive manufacturers on the market not named Lotus, Porsche has probably the longest track record (pun fully intended) of keeping each sporty model in the lineup as lightweight as possible, though the recent Panameras, Cayennes, and Taycans break from this tradition. But note, none of those models use a flat-six engine.
8 Porsche’s Flat-Six: Luftgekühlt
One of the premier automotive events in the world is Luftgekühlt, which celebrate’s Porsche’s air-cooled cars, from the 356 to the 911, 912, and 914. When Porsche switched to water-cooling in the 911 and the Boxster generations, known internally as the 996 and 986 gens, fans of the company were disheartened. There are pros and cons to both air-cooling and water-cooling, though Porsche would never have been able to keep air-cooling running until the late-1990s without the flat-six engine design. (Another bonus was Porsche’s commitment to dry-sump oiling, which has fallen by the wayside in anything other than Mezger-engined models like the 911 Turbo, GT3, and GT2 variants.)
7 Porsche’s Flat-Six: Easy To Service
Porsche likes to brag that over 70% of the cars ever to roll out of Stuttgart are still on the road today. While the stat definitely sounds good in marketing material, the reasons behind it are numerous. First, Porsches have always attracted a specific type of buyer or collector that wants to keep their car running. Values, meanwhile, don’t seem to suffer as much depreciation as other brands’ cars. Plus, the sporty characteristics of a Porsche make it less likely to feel obsolete only a few years later. And finally, Porsche is known for high build quality and reliability, part of which comes down to the fact that the company’s iconic flat-sixes are easy to service and maintain.
6 Porsche’s Flat-Six: Rear And Mid-Mounted
Porsche has long maintained a commitment to selling a lower-spec sports car that’s more attainable than the 911 flagship. This started with the flat-four-powered 912 and 914 in the 1960s, and was continued with the 944’s inline-four in the 1970s. The 914’s direct descendants are today’s Boxsters and Caymans, which use a similar flat-six as the 911 but smaller, producing less power, and mounted ahead of the rear axle for perfect balance. And the flat-six is a perfect engine for a mid-mounted layout, in addition to being great behind the rear axle on the 911.
5 Porsche’s Flat-Six: Tradition
Once upon a time, Porsche intended the 928 to replace the 911 altogether, as the automotive industry moved towards water-cooling, front-mounted powerplants, and grand tourers. Porsche purists grated at the idea, though, so the 911 remains in the lineup as almost a statement of Porsche’s commitment to tradition, even if it does have some inherent flaws that are solved in the Boxster and Cayman mid-engined layout. Regardless, the flat-six will almost certainly remain part and parcel of the 911 forever, as Porsche has clearly learned its lesson.
4 BMW’s Inline-Six: Perfect Balance
Much like Porsche’s flat-sixes, BMW’s inline-six engines have perfect balance due to opposing forces creating by moving pistons. As each piston in a combustion stroke is counterbalanced by a matched cylinder in an induction stroke, all symmetrically oriented around a crankshaft, there’s no need for a balance shaft or counterweights. This contributes to the straight-six’s smooth revs and great sound.
3 BMW’s Inline-Six: Lightweight
Again, like Porsche’s opposing cylinders and how they reduce the number of parts in the engine’s construction, BMW employs inline-sixes because they can be lighter in weight than a V6 producing the same power output. And for a company that prides itself on creating “The Ultimate Driving Machine,” keeping curb weights low should be a priority (even if BMW has somewhat lost sight of this fact across the lineup).
2 BMW’s Inline-Six: Weight Distribution
Take a look at any BMW on the market (other than the utter disappointment that is the new, front-wheel-drive 2 Series), and one thing that stands out about the company’s designs is how close to the front of the car the front wheels are. This contrast is especially notable when compared to cars from rival German manufacturer Audi, which tends to mount engines ahead of the front axle. But BMW keeps the inline-six behind the front axle to help maintain as close to a perfect 50:50 front-to-rear weight distribution as possible.
1 BMW’s Inline-Six: Tradition
In the end, BMW became famous for its straight-six engines, going all the way back to the E21-generation 3 Series. When the E36 M3 took on a straight-six and the E46 followed suit, the tradition had become ingrained in BMW culture so much so that the E92’s V8 was met with ridicule and revulsion. Today, the M3 once again features an inline-six, though it has received some forced induction to produce massive power figures, as well.
Sources: Porsche, BMW Guide, Lotus Cars, and Wikipedia.
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