Not a company to stand still for long, Porsche was constantly looking for ways to improve its engines in the ‘60s. Somehow the Type 916 twin-cam 6-cylinder engine always seemed to miss the limelight…not anymore!
The promotional brochure gave the power output of the new Porsche 917 as 520bhp when it was launched at the Geneva Motor Show on 12 March 1969. The engine powering the revolutionary 917 was a 12-cylinder boxer unit of 4494cc capacity, which up until that point, was the largest capacity racing engine that Porsche had built. The Type 912 12-cylinder engine, correctly referred to as a 180 degree V12, was a large lump, and featured gear-driven cams instead of the double chain system that drove the cams on Porsche’s other engines.
‘What’, one might ask, ‘is the link between Porsche’s mighty 12-cylinder 917 engine and their traditional 6-cylinder 911 engine’? The answer lies in a little known but technologically important experimental engine called the Type 916, a twin-cam 2-litre 6-cylinder engine. Very little is known about this unit outside of Porsche’s experimental racing department, and therefore not much has been written on this missing link over the years.
Hans Mezger, Head of Engine Design at Porsche remembers, “It was Ferdinand Piëch’s idea, we worked together in Zuffenhausen at that time. He was in the engine experimental department and I was in the engine design department but we worked together on the original 6-cylinder engine, which by the way was also his idea. But then he wanted to improve the production 911 engine by using four camshafts instead of only two.”
Porsche engineers had been experiencing some problems on both their racing as well as production engines with the cam followers on the two-camshaft version because the cam follower used a rocker arm and not a cup-shaped follower. Improvements to the 6-cylinder engine included trying a number of different surface coatings to address wear problems and to achieve higher engine revs in order to produce more power.
The engineers at Porsche designed the boxer engine in such a way so that by adding cylinders engine capacity could be increased relatively easily. The engineers at Ferrari, Jaguar and others, who, when they wanted to develop a larger capacity engine, would have to basically create a whole new sub-assembly and top end which was a much bigger undertaking. With the cylinders and cylinder heads all being separate units, the Porsche engineers in the engine design department could increase the number of cylinders, and thereby the capacity, by building a longer crankcase (fabricated by either Honzel or Mahle) to accommodate two extra pots, which is how the 8-cylinder engine came about.
According to Hans Mezger, there had been a plan in existence from early on that allowed for a 4-cylinder, a 6-cylinder, and an 8-cylinder engine to be available in this manner. In this way, the 3-litre 908 engine was itself a development of the 2-litre 6-cylinder engine, as Hans Mezger points out, “We had a new project which was the 3-litre 8-cylinder, which we had to develop in a very short time, that’s why we didn’t change anything. Of course, we had to change the crankcase for the 8-cylinder, and some other castings like the camshaft housing, but not the cylinder and cylinder heads because we used separate cylinders. On all our engines, racing as well as the production, they all used singular cylinders and cylinder heads, so we could exchange these on all engines.”
“By adding two additional cylinders to the Type 916 engine, we got the 908 engine, which was just a 3-litre engine,” Mezger explained. Actually, it was a little more complicated than that, because the engineers took the 2-litre engine cylinder dimensions with the standard 80x66mm bore and stroke and increased the bore to 85mm, which with the same stroke, gave the 8-cylinder 908 engine a capacity of 2997cc. However complex an operation that may sound to the average car enthusiast, to a racing engineer it was a fairly straightforward concept. The 12-cylinder Type 912 engine in the Porsche 917 was again a derivative of the same basic 6-cylinder engine, and had the same 85x66mm cylinder dimensions as the 908 8-cylinder engine, but with two extra pots added at each end of the crankcase.
The Type 916 project gathered speed when Ferdinand Piëch approached Valentin Schaeffer, Chief Race Engineer (Engines), for an estimation on how long it would take him to build a 4-cam engine. Schaeffer, who had the privilege of working on every Porsche race engine between 1955 and 1989, recalls, “At first Mr. Piëch asked another engineer from the production side, how long it would take and he said he would need six or seven months. Then he came to me and asked the same question and I said five weeks, so he said ‘make it.’”
Schaeffer remembers that the Type 916 study, to see what could be done with a 4-cam 6-cylinder engine, started in about 1966 or 1967. Actual work, though, only began on this engine in late ’67 and this was then developed at the same time as the 4-cam 908 engine, the latter engine only running on the dyno for the first time in December 1967. A list of what was needed in order to build the Type 916 engine was drawn up and it took some time for Schaeffer to assemble all the components, including the new camshaft housings, before work could begin. Schaeffer, “We used components from the 906 engine including the valves, and I only ordered a few small things but it took about two months before I had all the parts, and then I started. I needed four or five weeks, no more, and we built just one engine in our race shop.” This first engine was a 1991cc 4-cam engine that utilised the standard 911 or 906 crankshaft (made by Alfing of Wasseralfingen), with a 66mm stroke. At this stage, the 2-litre production engine was the largest engine that Porsche could practically use as a base unit for this development. The resultant Type 916 engine, regarded as very much an experimental engine, was then dyno tested and just a few small changes were necessary according to Schaeffer.
The 916 engine differed from the 2-litre 906 engine only insofar as it had 4-cams, but it was otherwise the same, a full race, open engine with no filters on the intake system. However, the intakes and mufflers were different from the 906 because the engine was located at the rear and not in a mid-engine position. About the 906 camshaft Schaeffer recalls, “It was very heavy in the first 916 engine, I think it was about 3kg [per cam], and so we made different camshafts, and the inside was hole-bored to make it lighter.”
The motivation behind this project, however, was not to develop a twin-cam six, but to explore Piëch’s dream of having bigger and more powerful engines to power his crop of revolutionary ‘plastic’ race cars. Schaeffer recalls, “Mr. Piëch said to me, ‘how long do you think you will take to find out how much horsepower you can get?’” The power developed by the Type 916 engine was little more than the 906 unit, as Jo Siffert commented. Valentin Schaeffer again, “One time I remember in Mugello, Italy, Siffert said at this time that it was not much better than a normal  engine. But of course, this engine was not tested or developed and I didn’t make a proper injection cam for it.”
Driven by Ferdinand Piëch’s ambition to rise to the top of the world of endurance motor racing pyramid, he pushed the race engine development team to come up with the horsepower numbers on the 916 engine. The idea of the Porsche 917 was already developing in his mind, and he knew that he wanted a twelve-cylinder engine, and what better way to get an accurate idea of power potential than to extrapolate the output achieved by a 4-cam engine of half the desired 4.5-litre capacity. Schaeffer then proceeded to increase the capacity of the Type 916 from 2-litre to 2.25-litre, exactly half the capacity of the 917’s Type 912 engine.
In order to cut down on time, the development team used the standard stroke 66mm crankshaft and so the increase in the capacity of the Type 916 engine came by way of an increase in the bore. Pistons and cylinders were supplied by Mahle as normal, and the same valves were used, just slightly larger in size and the Bosch fuel injection was carried over from the 906. The 2.25-litre engine certainly showed some potential but this was before any development work had been done. This experimental engine was developed in his spare time, as Schaeffer explains, “I had to attend all the races and do all the dyno work, and so I had a lot of work do, this [Type 916] engine was just built on the side.”
Egon Alber, Master Mechanic in charge of rally cars at Porsche, designed the tailpipe of the rally 911 R using parts from the 904 exhaust. It was so effective that with just a few minor changes, homologation for road use would have been possible as well.
In principle, the 917’s engine used much of the experience and lessons learned from the development of the Type 916 six-cylinder engine and that of the 3-litre 908 eight-cylinder engine. Hans Mezger again, “The  engine itself was completely new because we had a central internal driveshaft with gears in the middle of the engine for the camshaft drive instead of chains. It was completely different, but to save time we used the same units in principle such as the cylinder heads and Mahle pistons and liners. In both the 908 and the 917 we used titanium conrods, and these were also used in the experimental [Type] 916 engine which of course came from the 906.”
To save time and development costs on the 917 twelve-cylinder engine, and in accordance with Piëch’s instruction, Valentin Schaeffer tested the 2.25-litre Type 916 engine treating it as half of the Type 912’s full 4.5-litre capacity. Mezger recalls that they had a very short time in which to develop the 917 engine, and so the development of the Type 916 engine was critical to the 917. Mezger explains, “We used the 6-cylinder 916 because if you put it on the dyno you could tune the engine as half, or 50 percent, of the displacement of the 917 engine. We did a lot of testing with the 4-cam 6-cylinder 2.25-litre engine on the dyno to find out what power it developed, and to save time.”
The importance of this work becomes apparent when, at the Geneva Motor Show on 12 March 1969, the Porsche 917 was shown to the public for the first time. On the dyno, the Type 916 2.25-litre engine had shown a power output of 260bhp, and this was significant for Ferdinand Piëch’s overall motorsport plans. Hans Mezger explains why, “260bhp was very important because all the brochures for the Geneva Motor Show, where the 917 car was shown to the public for the first time, announced that the engine produced 520bhp. This was derived from the power we had seen on the 6-cylinder engine, but the first actual power reading on the 12-cylinder engine showed exactly 542bhp, I will never forget it, and this showed that it was a very successful design. In any case, we expected more power on the 12-cylinder engine, because we implemented many improvements to reduce friction losses.”
For the 1968 season, Porsche wanted to push the 911 on the motorsport front, in particular on the rally scene, but not before Schaeffer had the fuel injection system correctly adapted for the 916 engine. The factory also entered one race with the 916 engine, which powered a 911 R at Mugello in 1968. Schaeffer remembers that the car performed well in that race, but as there was not a real need or specific application for them in endurance racing. Schaeffer admits, “It was not really fully developed, we only made it on the side, and after that nobody needed this engine. We built four or five engines at this time and then I handed them over to the rally shop.”
It is well known that Vic Elford tried to coax a reluctant Porsche management to enter rallying in the 1960s. But it was only after some encouraging results in 1966/67 in which he entered and ran a 911 S provided by the factory (with no works support), that the factory sat up and took notice.
“I loved the Corsica Rally and I finished third there the first time and then I was third again the second time in 1967. So, for the 1968 Corsica, Porsche said we could take a 911 R, but not just the ‘normal’ 911 R, this one was fitted with the twin cam engine,” Elford recalled with a smile.
The roads making up the Corsica route were typically bumpy being normal public roads, and with the 911 R being so light (830kg versus 1030kg for a 1967 911 S), Elford would leave the ground regularly and come back down with a hefty bump. This harsh treatment placed undue stress on the car’s suspension and Elford remembered breaking rear drive shafts during practice. Fortunately, Elford was given two 911 Rs for the event, one for practice and one for the race itself.
However, even in international motorsport there are some who will go to great lengths to deter the opposition. Elford again, “I was the favourite to win, and I most certainly would have done, but my car was sabotaged in the parc ferme in Bastia. At the start, we came out of Bastia and climbed to the top of the mountain on the other side of the island ready for the start of the first special stage. Suddenly my oil pressure dropped and so we got out, went to the back and lifted the hood to find that there was oil everywhere because the oil filter had been unscrewed!”
With their chances scuppered, Elford turned the car around and coasted back down to Bastia. Nothing could be proven though, and the organisers just shrugged their shoulders saying that the mechanics must have forgotten to tighten it.
During another event in 1968, the Criterium des Cevennes in southwestern France, Elford encountered the same problem with the drive shafts. The route was slightly shorter than the Corsica event, but the roads were similar and the drivers had to do one complete loop of the route at night, have an hour off for breakfast in the morning, and then do the entire loop again in daylight on Sunday morning. Each loop of about 500 miles would take between 7-8 hours to complete, Elford shared. “After the night loop, I was way out in front in the 911 R and in the daytime loop I got about halfway around and ‘bang’, one of the rear driveshafts went,” he recalled.
On the 916 engine itself, Elford had this to say, “It was a phenomenal engine. At that time all 911 engines, both standard and race engines, revved to 7200 rpm, which was the limit for the 6-cylinder engine. But the 4-cam revved to 8200 rpm and it had an almost flat torque curve from about 3000 rpm to 8000, it just had torque all the way through and it was just phenomenal to drive.”
In an interview with the author, Hans Mezger could not remember any specific problems relating to the drive shafts, or why they should have broken as Elford had pointed out. Mezger explained, “The engine was just an experimental engine and we had many new ideas, for instance, we did a lot with titanium parts to make the cars and engines lighter. On the Rally Corsica, we used titanium bolts instead of steel bolts, but on that car we also tested aluminium bolts which were even lighter than titanium, but not as good.” Mezger’s recollections would certainly seem to explain that it was the aluminium drive shaft bolts that gave way when Elford returned to earth each time after flying over a bump.
As Hans Mezger pointed out, the Type 916 engine was just another experimental engine for Porsche, but one which played a vital role in the development of the 4-cam 908 eight-cylinder engine, and later the 917 engine. “But it was always a works engine, all of these engines were from the factory,” Mezger stated.
Unfortunately, when the Race Engine Department moved from Zuffenhausen to Weissach, the area they had occupied was taken over by a new department, the Special Wishes Department. Many of the engineering papers and drawings that Schaeffer had at the time were trashed by the incoming personnel.
Egon Alber recalls, “Ferdinand Piëch also wanted to use this engine in the production 911 but technically that would have been rather difficult to implement. The basic problem with this engine was the camshaft chain because, until the engine had reached its operating temperature the chain was too long, but once the operating temperature was reached, the chain was then too tight.”
The Type 916 engines were eventually sold to a race team in Rosenheim, Bavaria, who went on to use these engines to great effect. The team, KMW, was made up of Jo Karasek (team principal), Hans Müller Perschl (manager and driver) and Manfred Weiß (who built the cars). These KMW Porsches closely resembled the Porsche 908 Spyder of the day, and it was said that these cars regularly embarrassed the highly professional and sophisticated works racers. No longer needed by the factory, perhaps this was the right way for such an important piece of the Porsche’s engineering heritage to see out its days.
Although so few of the Type 916 engines were made, they played a vital role in helping Porsche to achieve its crowning glory just two years later when the 12-cylinder 917 took overall honours at Le Mans. If an engine could speak, it might just tell of its pride in playing a part in helping the company to record this all-important victory, their first of nineteen overall wins, by far the highest tally for any manufacturer. That’s some heritage to speak of…
Written by: Glen Smale
Images by: Porsche Archives