It was the late 1960s, and the Ford Motor Company’s indestructible engine program was on a roll, with the 7.0L-powered GT40 crushing the competition at every curve. Eventually, the trouncing became so intense, that the rulebooks had to be rewritten to allow a more even playing field, immediately extinguishing the GT40’s hopes of seeing another season. This rule change meant engines had to have a displacement of no more than 5,000cc, or 5.0 liters, and Porsche was one of the most eager to make a move.

Underpowered, outperformed, and problematic in regard to vibration from the race-exclusive 8-cylinder Boxer design, the old race car engine program was set aside for spare parts, and Porsche’s engineers quickly got to work. And note the emphasis on the word “quickly” in that last sentence. Porsche needed to have a working, homologated 12-cylinder prototype ready for display and testing within less than a year.

Crafting a bigger, brand-new engine from scratch, while recycling what was known to work well within previous test mules proved to be key, and before long the development of the Porsche 912 engine emerged, along with a legacy that would last for decades to come.

Eventually, this would lead to the spin-off creation of one of the largest, and rarest European race car engines of all time: the Porsche flat-16. An engine that was capable of extreme power figures and was destined for racing in America, but ultimately failed to make the cut at the last minute.

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According to Porsche’s historical annals on the 917, the whole project kicked off when the Head of Development at the time, Ferdinand Piëch, instructed Chief Engineer Hans Mezger with the task of constructing a new 5-liter Le Mans race engine, as well as a car to put it in. The team was only given 10 months to complete the project, as Piëch wanted to reveal the car at the 1969 Geneva Motor Show.

What emerged was a V12 engine blueprint that to the untrained eye, may have appeared all the world like two 6-cylinder 2.2-liter 911 engines slapped together. The powerplant’s overall length was surprisingly short for having so many cylinders, which was due in part to the use of a 180-degree bank angle and a clever “recycling program.”

Since Mezger was all about expounding upon what had been proven to work well, and he didn’t have the time to craft brand-new internals from scratch, the 912 engine was constructed to use internals pulled from the 3.0-liter 908 engine. Some of these include its pistons, cylinder design, and valves. In true Porsche fashion, the engine was also air-cooled via a horizontally mounted top cooling fan. But outside of that, and the recycled parts off the old 908, this engine was unlike anything Porsche had produced to date.

To save weight, the dry-sump oiled bottom end of the engine housing was made out of magnesium, while the heads were an all-aluminum affair. Up top, each cylinder bank utilized gears that spun off the central power take-off, which in turn powered the dual overhead camshafts inside their internal magnesium journal housings. Being that this was a twin-valve, twin-spark configuration, a total of 24 sodium-filled valves and a separate two-dozen spark plugs were implemented, which surely required one hell of a lengthy tune-up.

Now as for the mechanical fuel induction portion of the 912 motor, that was provided by an overhead Bosch pump specifically built for a 12-cylinder V-configured engine and adapted to the flat-12. It may sound and look a bit janky, but those dozen plastic tubes and trumpets delivered fuel extremely well. Slide throttles outfitted with steel ball bearings controlled by a single linkage gave the blend a trapdoor-style drop into the intake ports, and onward to combustion.

Equally odd-looking, but just as effective, were the fiberglass air shrouds that encased portions of the engine. These are those khaki-colored portions of the engine you see, and they were what channeled the cool air pulled in by the crankshaft-driven fan, and forced it upon each cylinder.

Then there were the exhaust manifolds, which saw numerous revisions over the years. What began with four individual short-runner headers, each pumping smoky excrement out of three assigned cylinders, was soon abandoned for more practical and safe performance designs. According to sources, it wasn’t the two exhaust ports jutting out the rear that was the issue, but the duo of tubes dumping smoke in front of the rear wheels that posed a problem.

Blockhead Thinking Redefined

But everything that was the 912 engine, and the 16-cylinder behemoth that was born from it, began in the block. It was here that the crankshaft served as the cornerstone for the entirety of the architecture surrounding it. It may have been a shorter 12-banger, but that one-piece crank is still pretty damn lengthy, and at 55.6 pounds, quite heavy too.

Since this engine was unlike anything else Porsche had done to date, and Mezger had been given both the funding and freedom to build as he pleased, his bespoke crank came outfitted with redesigned, non-split journals for greater lubrication and reliability. These were accompanied by eight ultra-wide main bearings (instead of the typical fourteen) and six crank pins, as well as the use of titanium connecting rods from the old 908.

Regarding the center gear on the crankshaft, that was a design bred out of necessity. Due to the length of the crank, it was unable to withstand continuous exposure to substantial sums of power twisting at its ends. Whereas the center section was far more secure, and absorbed and distributed power in a much more even and linear fashion.

As for where this crazy crankshaft sent all that power, that was a tale of two very different directions. All of the juice sent to the upper intermediate shaft kept accessories like distributors and alternators firing properly and doubled as an assistant when engine timing was being determined and/or adjusted. The lower, stubbier output shaft on the other hand had the sole purpose of sending power to the pavement.

That magnesium crankcase was quite the complex affair as well, at least from a metallurgy standpoint… All of the bolts used to hold the block housing together may have been titanium, but the internal bolts were a bigger concern, for they had to play nice with the magnesium crankcase too. Use of the wrong metal could potentially mean expansion, contraction, and/or corrosion in race-temperature situations when coming into contact with the magnesium.

This proved to be a significant stumbling block and one that was only remedied when bolts containing a steel alloy known as “Dilavar” were implemented. Formed with 6 percent manganese and as much as 13 percent nickel per bolt, these specialized Dilavar bolts handled head bolt duties and other internal affairs and proved to be extremely capable once equipped with spherical washers.

While finned outer cylinder walls allowed greater cooling capacity, chrome-plated bores filled with forged aluminum pistons pushed the tempo. Domed and valve cut, each piston came loaded with two compression rings near its crown and an oil ring below the gudgeon portion of the connecting rod pin.

Gear-driven oil pumps came in threes on these engines, with the first playing the position of chief pressure pump, with its two siblings scavenging whatever was left for crankcase cooling and oiling recirculation. All three were crankcase positioned, and driven by the same output shaft that sent power to the clutch, with one pump running off the exhaust camshaft. This allowed the hot oil to be sent to the oil cooler as necessary once thermostatic control thresholds were breached.

However, being that the crankshaft was completely devoid of a drive system, Mezger had to come up with a plan for getting oil to those hulking bearings on each end of the crankshaft and up underneath the domed pistons. Fortunately, testing found that this design could run just fine on lower oil pressure, and therefore did not need engine speed to keep things oiled as long as the jets beneath the pistons were spraying as designed.

First incarnations of the Porsche 912 engine came with a 10.5:1 compression ratio, creating 580 horsepower at 8,400 rpm, and 376 pound-feet of torque at 6,800 rpm. This rocketed drivers to over 210 mph, but came with a very genuine concern of crashing due to the vehicle not having enough downforce. A danger that was hammered home when a 917 killed a driver on lap one of the car’s first outing.

American Aspirations of Porsche Racing

Since displacement came in at just a tick under 4.5-liters, Porsche’s engineers were left with plenty of wiggle room in case the 12-cylinder motor required further revision for more power or homologation requirements. This would eventually lead to the development of 4.9-liter and 5.0-liter versions of the 912 engine, and Porsche’s shift to racing on the other side of the pond.

Looking to compete in the American Can-Am Series, but still underperforming in the power department, Porsche came to the conclusion that its 12-cylinder 912 required some additional oomph. And being that this was the early 1970s, the whole “bigger is better” mindset was still very much a thing.

So a 16-cylinder prototype was developed, which Mezger made fully scalable anywhere from 6.0 to 7.2 liters. Genetically, this engine’s overall design was pretty much just an upsized version of the 912 engine, but with an extra four cylinders on board.

Measuring in at 7.2-liters, Mezger’s flat-16 generated 880 horsepower at 8,000 rpm without the use of boost. Upon completion, the massive flat-16 was dropped in a tweaked 917 chassis with an expanded rear engine compartment, and away it went. As best as anyone can tell, Porsche only made four of these prototype engines, all of which were intended to compete in the American Can-Am Series.

Testing was primarily completed with race legend Mark Donohue behind the wheel, who after exiting the car from one of its first shakedowns, decreed that the 917 flat-16 was “a monster,” and that he could easily see the motor reaching 2,000 horsepower with a couple of turbos on board. Unfortunately, this engine also weighed a whopping 80 kilograms (176 pounds) more than the normal 912 and required additional redesigning of the chassis for extension, support, balance, and safety.

Sadly, this additional weight and the extensive redesign requirements that came with it led to Porsche’s massive flat engine going absolutely nowhere, and not once did it enter a race. Instead, the entire 16-cylinder Porsche program was axed in favor of a lighter and smaller turbocharged 912. An engine that by today’s standards still reigns as one of greatest race engines ever constructed, as it absolutely trounced the field. So much so, that the Can-Am rulebook had to eventually be modified to level the playing field, which subsequently put the potent 912 out to pasture.

So what of those four 16-cylinder screamer prototypes Porsche created? Today, only two are documented to still be in existence. One of which you will find at the Porsche museum in Stuttgart, Germany, where to this day it still sits inside the white 917 prototype car it had originally been mated to in 1971.