Some historical musings: the Porsche 917

[J.D.]

A little while ago MotorSport magazine; the legendary “Green Bible” of motor sport, conducted a survey, the results of which would come as no surprise to anyone. The quest was to establish the greatest racing car of all time. I don’t know what candidates were nominated but the Porsche 917 won it in an apparent canter.

Everyone with even a vague interest in motor sport knows the 917. The legendary Gulf-Wyer blue and orange cars were so prominently featured in the 1970 film “Le Mans” that they are probably seared into the memory of everyone who saw the film. The racers of the era were not failed or retired F1 aspirants but top drivers in their own right who often balanced their F1 careers with those of sports car racing.

The 917s development was fairly straightforward. Following the win at Le Mans by the Ford MkIV in 1967, the elephantine American V8s were consigned to history. Another rule change in the late 1960s opened up the possibility of a limited run of 5 litre “specials” being built for sports car racing in 1969. Both Ferrari and Porsche stepped up to the plate.

Ferrari chose a development of their existing V12s. Porsche chose to expand on the already developed 3 litre, 8 cylinder 908. They chose to use the same pistons, connecting rods, basic valve gear and many other shared components to create a 4.5 litre 12 cylinder version of basically the same engine.

There were developmental differences. The air cooled engine required gaps between the cylinders for cooling air, meaning that the engine flexed a lot, requiring the power take off to be in the middle of the crankshaft where the fan drive was. Porsche engineers also chose a slightly narrower valve angle for their new flat 12.

The aim was to produce an engine with the same 120 hp per litre power output as the 908. At the time a Ford Cosworth DFV F1 engine developed about 450 hp – 150 hp/litre. This meant that the new flat 12 should be good for about 540 hp. Eventual expansion to 4.9 and ultimately 5 litres took the power to 630 hp.

The first 917s had serious problems with aerodynamic stability. Work over the winter of 1969/70 resulted in the 917K (“Kurtz” or short tail) and also the 917LH (“Langheck” or long tail). Porsche chose a dual-path development. The 908 would continue to be used on circuits like the Nurburgring and Madonie where agility was more important than outright speed. The 917s would be expected to dominate on faster circuits like Le Mans, Spa and the Oesterreichring.

By 1971, Porsche engineers, in conjunction with S.E.R.A. had developed the aerodynamic package even further and released three new or newish models at the April test weekend at Le Mans.

The original 917K now sported twin vertical fins. There was a new version of the LH with revised aerodynamics virtually all round and there was the curious 917/20, known as the “Pink Pig” which sought to combine the stability of the K model with the slipperiness of the LH.

It was during this weekend that Jackie Oliver is alleged to have driven a 917 on the Mulsanne straight at 240 mph, an unheard of speed at the time. Porsche engineers had apparently predicted a theoretical top speed of 239mph.

So the legend started.

The 1971 race was not quite a 917 benefit but it was close. The LH models had problems with overheating rear wheel bearings due to the partially enclosed bodywork and a K model driven by Dr Helmut Marko (now at RBR) and Gijs van Lennep won the race with a distance record which stands to this day (of course the track has changed considerably since).

Subsequent to all this, it became an assumption that the 917 did 240mph. Furthermore, it became an assumption that all models of the 917 were capable of such speeds. Then it was remembered that the LH was faster and a top speed of 246mph was propounded by notable motoring writer Ian Bamsey. He had originally reported Oliver’s 240mph run from April 1971.

More recently, the eminent Derek Bell has chimed in with 246 figure in a video about the 917. Confusion now reigns supreme and the longer it goes on, the more ridiculous the claims made for this car become. I have seen references to 917s producing 1200hp in Le Mans trim and doing 258mph. This has become ridiculous and clearly some people don’t realise that the only 917s to produce that much power were the turbocharged Can Am 917/30s. No 917 that appeared at Le Mans ever produced that much power.

Needless to say, nobody has quoted any sources whatsoever for these claims. Not that I’ve seen anyway.

Given that the Ferrari 512 produced 600hp in 1971, you’d think they would have just gracefully tossed in the towel.

Suspicious of most of this, I contacted Mike Fuller (AKA: “Mulsanne Mike”) from http://www.mulsannescorner.com to see what he had on the subject. For those of you who do not know this site, it is an incredibly useful resource for articles which go back many years. Mike, himself, has been involved in racing at Champ Car levels and that includes aerodynamic research.

http://www.mulsannescorner.com/maxspeed.htm is a list of the highest speeds reached on the Mulsanne straight from 1961 to 1990 and it makes for some interesting reading. These figures were established by the ACO speed trap on the Mulsanne straight and while there have been errors in the past, it is possible to draw some interesting conclusions.

First of all, according to the ACO figures, no 917 ever did 240mph during official practice or the actual race. In 1969, the 917 was the fastest car on the straight in both practice and the race, achieving 193.4 and 197.8mph respectively. In 1970, those figures were 199 and 205.2mph, both for a 917. In 1971 the speeds went up quite a bit but the surprise was the Ferrari 512 which did 222.6mph in practice. The 917 went a bit quicker in the race at 224.4mph.

In fairness, it is possible that the speed trap was incorrectly positioned – there are examples of this - and that the cars’ speeds may have been a little bit different but the error is unlikely to produce anything that would seriously affect the result. However, legend says the 917 did 240mph – an error of +10% - so let’s start with that assumption and see what happens.

Mike did some number crunching and he points out that that these are guesstimates at best and assume perfect conditions. Here's some of what he came up with:

600 hp (90% efficiency given power losses so 540 @ the wheels)
1.8 m2 frontal area
.30 cd

Plugging that in we get a estimate terminal velocity of 238.4 mph. To actually achieve 246 mph we need to bump power to 595 hp at the wheels (or 661 hp at the flywheel). Or keeping power the same, we'd need a reduction in cd to .272 which isn't realistic by 1970's standards. Keeping cd and power at the initial numbers, we'd have to reduce frontal area to 1.63 m2 to achieve 246 mph.

After some changes in details, based on some educated guesses:

600 hp (90% efficiency given power losses so 540 @ the wheels)
1.72 m2 frontal area
.36 cd

We get a terminal velocity of 227.7 mph which is cutting close to the ACO's 224.4 mph.

Mike went into it a bit further – much further than I was able to get - and came up with more. The Cx and Cd figures come from Paul Frere's book:

600 hp (90% efficiency given power losses so 540 @ the wheels)
1.57 m^2 frontal area
.33 cd

Yields 241.7 mph. We're getting closer to 246 mph. Getting back to the root question, could the 917 have done 246? I'd now have to say yes, very possibly. Consider, with setup changes, additional drag could have been shed off the car for increased straight line speed even if it destabilized the car (say a qualifying setup). A reduction in cd to .32 yields 244.2 mph. Bump power to 611 (550 at the wheels) and we're at 245.7, job done.

Okay, it was possible for a Langheck, especially if the originally quoted figure of 630hp is used. On the matter of the Kurtz it was a little different:

"Standard" 917K (guessing 1970 spec):

600 hp (90% efficiency given power losses so 540 @ the wheels)
1.546 m2 frontal area
.447 cd
220.9 mph

Gulf 917K:

600 hp (90% efficiency given power losses so 540 @ the wheels)
1.546 m2 frontal area
.438 cd
222.4 mph

Did they actually do 240? I don’t know. Was it a regular thing? Probably not. Certainly the ACO speed trap figures don't corroborate the story but they don't deny what happened in April either. If anyone here has any information on the matter, I'm all ears.

The 240mph claim for Oliver’s car has been around for as long as I have held any interest in the matter. Since I have not yet seen any data other than basic claims from motoring writers, I have no proof. I tend to give it credence based on the fact that I have heard it so many times and until recently it had not changed.

I’d like to publicly thank Mike Fuller for his help and interest in this. He went way above and beyond what I hoped for and gave me some extremely detailed and interesting answers, not all of which I had expected to hear. As something of an iconoclast, I can’t say I’m totally unbiased: I tend not to believe some of the things I read if they are not properly referenced.

Any errors or opinions are mine.

[w00dsy]

great post, some terrific info there

[J.D.]

great post, some terrific info there

My pleasure Woodsy.

I strongly recommend you go to Mike's site. The quality of the information you'll find there is first rate and extremely reliable. As a source, it really doesn't have an equivalent that I've seen.

[pixelboy]

Awesome post about an awesome car!! Well done

Had to post a pic

[Exar Kun]

One of the few non-fiction books i've read cover to cover in recent years was Porsche 917: The Winning Formula by Peter Morgan. It's a fantastic read. I bough an Exoto 917-30 too which remains my favourite 1:18 model. I just love everything about this car. Haven't been to Mulsanne corner in years but will head back now.

Great post JD - enjoyed going over the 917 once again.

[J.D.]

Cheers fellas.

I wrote this stuff mainly to try to keep some things in proportion. The biggest problem is that there seems to be an internet bidding war going on to see who can make the most outrageous claim for the 917. I think if I posted something which said that it produced the same amount of power as a WWII Messerschmitt and was just as fast, I'm sure I'd get some support. It's a question of what people want to believe.

I don't think there is much doubt that it deserves its status as the greatest and most iconic racer of all time. The success of that program effectively paved the way for later success with the 936 and again with the 956/962. The Porsche company of today owes much of its success to the 917. The trouble is that exaggeration of its performance does nothing to enhance its real reputation. It just creates a myth which goes beyond what were already remarkable capabilities.

If Oliver really did do 240 mph - a I believe on balance he probably did - it was a a truly amazing achievement and apparently not beyond the capability of the car but it was a whole 27mph faster than anything seen before; around a 12% improvement in top speed. That doesn't sound like much but when you take into account the fact that drag increases with the square of the velocity, you can see that it takes a lot more than just engine power and longer gearing to get there. Aerodynamic drag becomes the biggest factor by far and the increase is exponential, not linear.

In short, Oliver's performance was probably a one-off. Not a fluke but not par for the course either.

In race terms, 240 mph is unlikely and the ACO figures don't support it. 220mph is probably closer to the mark. And that's still bloody fast by any standard, much less 1971.

[Dr. Pain]

Nice post. I believe he did 240mph. But after reading what the '69 917 was like at speed I think the drivers didn't want to take the risk of going that fast and in a 24 hour race if you are already a good amount faster than the opposition then why risk it. The car was awesome and I think it's a shame that Ferrari arsed about so much back then because the 512 showed it was bloody fast. There are some nice clips on youtube about 917, drivers talking about it.

[AstrO]

[Dr. Pain]

Thats some of the vids

[J.D.]

Nice post. I believe he did 240mph.

I accept it with reservations. It's the only figure for which I have no actual evidence so it's the one I'm most suspicious of. It's also well out of kilter with the ACO figures from the race. That said, Mike Fuller's rough calculations show that it was entirely possible.

We are still researching this. At this stage the best evidence we have is that it was actually clocked at 236mph but the aerodynamicists from S.E.R.A. immediately questioned it, saying that it should have been 3.7mph faster*. The lack of information on the matter makes it hard to determine but I think Mike sheds some light on this in his assessment. As I say: we are still researching this one.

I have a hard time accepting the 246 figure though. I have only heard that from two people: Ian Bamsey and Derek Bell. I like Bell but I don't do chin ups on everything he says. Bamsey actually changed his story but he gives no reason for doing this.

But after reading what the '69 917 was like at speed I think the drivers didn't want to take the risk of going that fast and in a 24 hour race if you are already a good amount faster than the opposition then why risk it. The car was awesome and I think it's a shame that Ferrari arsed about so much back then because the 512 showed it was bloody fast.

The 917 was fast right out of the box. It's early aerodynamic problems limited its success though and I suspect they were never entirely solved. Even though it set standards for acceleration, braking and agility, the appearance of fins on the 1971 917K, as well as the "Pink Pig", suggest that there may still have been problems with directional snaking. Longitudinal stability would have been a pretty serious problem at 200+ on the Mulsanne because, as most realise, it's a public road with a crown in the middle of it. Get it wrong and you're a prime candidate for a synthetic funeral. Spa would have presented the same problems.

It's reliability was excellent, in spite of the flex, or maybe even because of it in some cases.

I don't know if you've read Frank Gardner's assessment of the 917 but it gives a tremendous insight into the quirks of the car as it was in 1969:

"I got a call from the competitions manager - and the money they were offering was certainly good enough to cross a strip of water and get in the thing. I think the reason they bestowed this honour on me was that every 917 driver was in hospital at the time, recovering from various stages of disrepair..."

As you read these words, it is essential to imagine them from the mouth of Frank himself, in a laconic, downbeat, Aussie drawl. "I remember that Piper did one lap in practice, and was all for going back to England, but I pleaded with him to stay because the money was right.

"This was one of the very first 917s, with an alloy chassis, which was gas-filled. There was a big gauge in the cockpit, which measured the gas pressure, and that was there to keep you informed of the chassis's condition. If it zeroed, they said, that meant that the chassis was broken, and I should drive mit care back to the pits.

"Once I knew what the gauge was for, I also knew that if it zeroed I wasn't going to drive it mit care anywhere. I was going to park the bastard there and then, pick up my Deutschmarks and get home to Mum...

"Then there was the engine. You had about 300 horsepower at 5000 revs, and then between 5000 and 6000 you picked up another 300! So it was a bit of delight, really, and it was on narrow nine-inch rims all round. The computer had said that nine-inch rims would make the car very quick in a straight line, but the computer wasn't strapped in the bloody seat up in the Eifel mountains, where you tend to get the odd corner..."

Nor was that the end of it. "You sat between these pannier tanks, which bulged when they put the fuel in. It took 40-odd gallons because it was pretty hungry."

It was also, even with ear plugs in place, quite extraordinarily noisy, to the point, Gardner said, of being disturbing. "It was bloody hard to think. You were horrified by all the activity, your brain numbed by the vibration, the power and the wheelspin.
"In those days they were still gas-welding chassis, and this thing flexed so much that the actual position of the gearchange used to alter. You'd reach out for where the lever had been last time you used it, and it wasn't there! It had moved.

"Nothing about the car was consistent, that was the thing. When it became airborne, sometimes it would sort of float through the air, and other times it would crash down. It never did the same thing twice. Just when you thought you had it worked out, it'd pull another trick.

"It was simply indescribable, the motor car, and the weather did its best to help, as well. Snow and rain all the way. You were just so crossed up in the thing that you didn't know which way was straight ahead in the finish. But we got it through to the end, seventh or somewhere, and in addition to paying me money, they did try to take up a collection for an Iron Cross, which they reckoned I'd earned..."

**

Obviously, development sorted out a lot of these issues. I have a feeling that the chassis flexibility would have been something of an asset on the Mulsanne because a stiffer chassis would tend to dart around more - increasing the likelihood of the aforementioned synthetic funeral - but that's just speculation on my part.

As for the Ferrari, I sort of see it as an unfulfilled potential legend. The racing would not have been the same without it and the fact that it was so good just shows how good the 917 really was. Like the 917, it was fast out of the box. It's poor showing in the 1970 race was because most of them were crashed early on. I'm not sure if any of them finished. I'll have to look that one up.

The biggest problem for the Ferrari teams was the lack of factory support. This was most definitely not a problem for the Porsche teams.

*via Mike Fuller.
**http://www.legslarry.org.uk/917.html

[Dr. Pain]

In the video La Ronde Infernale, Vic Elford does mention that they, being 917 drivers, were not going flat out down Mulsanne but the speed is approaching 240 mph in 1969. No matter how fast it is or isn't it's the most awe inspiring car and it's design showed how good it was when Kremer entered their homebuilt K-81. It did well at Brands till it had to retire. In a way I hope the research does show 240 mph but 246, well I'm with you on that. To have GT-40 then Porsche 917 hot on it's heels is magic. I love 'em

[J.D.]

Redman said much the same thing.

I don't know the Cx or Cd for the 1969 car and it was of a lower power than the 1971 car, on which most of these calculations were done. I think from memory the 4.5 litre version put out about 540-560 hp.

As I said, I think there's probably some truth in the 240 claim but not in practice or the race. The April test session was a different matter and we don't know what compromises Oliver made to get to that speed. Mike suggested this in one of his posts. The car could have been wandering all over the road for all I know. In fact, it probably was. Not a major problem in daylight when there's nobody else about but you could not say the same for a busy track at 3:00AM... You'd want it to be rock steady then.

[NeilPearson]

Guys, I have to say awesome read. I really enjoyed the Posts, and the vids. Thank you J.D. for this

[J.D.]

My pleasure Neil.

I went to the Porsche Museum website to see if there was any information about Cd or Cx for the three main models of 1971, as these were pretty much the ultimate refinements of the Group 5 917. I have still yet to find any of this information but this quote was noteworthy:

A 917 long-tail coupe model set a further record in 1971: On the Mulsanne straight stretch, which is part of the route in the Le Mans 24-Hour race, the sports car with the start number 21 recorded the highest speed of 387 kilometers per hour.

You will probably enjoy this. It's worth reading:

http://www.porsche.com/international/aboutporsche/pressreleases/archive2009/quarter1/?pool=international-de&id=2009-03-09

It is noteworthy that Porsche do not claim this as the standard top speed for the 917, nor do they say it happened during the race. They simply say it happened. This takes nothing away from the achievement, of course but rather backs up what I said earlier: that it was done during the April test session in 1971. The ACO have been reluctant to verify it because it did not happen at an official event.

What the ACO records and what the ACO decides is official are apparently two different things!! Oh well, Vive la France!

What is also notable is that the 917LH was not merely a Kurtz with a longer tail bolted on. While this was done in at least one case (the "Psychedelic Monster"), closer examination reveals that the side panels between the wheel arches were of a lower profile. In later versions the front air dam changed considerably too. The 1971 LH also had partially enclosed rear wheels. In short, the LH was a different aerodynamic package in many respects, as can be seen here:



While it would have been faster in a straight line than a Kurtz, the lack of Kamm effect (the stabilising effect of the blunt tail of the Kurtz) would have meant that car would have been less directionally stable. The addition of fins to the 1971 Kurtz might possibly have been the result of a lower profile rear deck which would have had the same effect.

But that's just my own speculation.

The one-off "Pink Pig" was a different package again and had much more bulbous front wheel arches as well as a lower rear deck. I have yet to establish anything of the performance of this car but it was quite capable of holding its own against the other models. Just what it was good at, I'm not sure.