Porsche double 8 cylinder ( 16 Cylinder ) engine

[Buchanan Automotive]

Carrying on from my post about early Porsche 8 Cylinder engines before the 928 , I thought I would mention one of my all time favorite Posche engine's ( the double 8 engine ) the normally aspirated Porsche 16 cylinder engine of 1969/1970 

 

It all started with the original bevel drive flat 8 cylinder 1.5L  engine ( engine type 753) back in 1960 as their formula 1 engine , this engine grew until it reached its max size of 2.2L as a sports car racing engine in the mid / late 1960's & was very successful in hillclimb events with the Porsche 910/8 Bergspyder , this 8 cylinder Porsche weighed in at just 410KG( thats the entire car) with 270HP at 9000RPM from its 2.0L 8 cylinder super complex bevel drive engine , but this car/engine size could never go for outright honours at LeMans 

 

So with Porsche looking at LeMans 24 hour outright wins ,a new larger engine / car would be needed & at that time the FIA would allow a small number of sports cars( 25 ) built with a max engine size of 3.0L with normal aspirated ( NA ), where as a 5.0L engine would require 50 cars built & homologated  

 

In September 1967 ( for the 1968 season ) Porsche developed a newer less complex  flat 8 cylinder engine, ( engine type 908) the 908 ( 3.0L ) chain driven at one end of the engine and quite conventional( 911 air-cooled conventional) in most ways , but this held some flaws 

 

Like the air-cooled 6 cylinder engines it had one con-rod per crank journal ( Boxer Design), this made the engine longer than it needed to be ,and it still utilised radially delivered oil pressure into the ends of the crankshaft to feed the con-rod journals / big-ends ( just like a road engine ) , this becomes a real flaw if you want this engine to rev real hard ( like 9000 RPM ) as the engine crank spins faster and faster the radially delivered oil pressure supply now has to compete against centrifugal forces pushing the oil back ( lower oil pressure getting into the crank ) even before it gets to the centre of the crank , so to overcome this Porsche had no other fix other than to keep increasing oil pressure until this engine needed 100PSI of oil pressure at 9000 RPM to keep the con-rod / big-end bearings safe

It was this new ( for 1968) 908 3.0L engine that Porsche could use standardised race parts / major components to make bigger capacity engines in the future "if required" ,semi mass production race components like the individual air cooled cylinders/pistons, individual cylinder heads & their valves & valve springs within the heads , none of these components were from the air cooled 911 engine , naturally the engine was double overhead cam with 2 valves per cylinder ( 4 valve with air cooling was not possible )

 

 

The new 908 was barely finished when the FIA changed the rules again ,instead of a minimum quantity of 50 vehicles to qualify for the "Series Sports Car " category with a 5 litre engine , it was now enough to build just 25 vehicles to enter races like LeMans 

This was a real wake up call for Porsche , suddenly there was a real threat that a competitor would enter a 5 L "race" sports car ( like Ferrari ) & Porsche would be stuck with the 3.0L engine size 

Without waiting for the FIA deal to be sealed , Porsche set to work immediately on another car with an engine up to 5L engine size .

When the FIA finally announced to the public in June 1968 about the 5L rule change , Porsche had engine concept ready to proceed , it would be a 12 cylinder ,180 degree V arrangement, meaning 2 con-rods per crank journal ( just like a 928 ) with central power take off as its outstanding design feature 

This new engine would carry a engine type number of 912 & the sports car it would go into would be the 917

Speed of production was the essence , so the new 12 cylinder magnesium crankcases were commissioned along with 12 cylinder crankshafts  , but the 908 ( already in race car production ) cylinders ,pistons , cylinder heads etc would be used in the new 12 cylinder engine , hence why the first batch of the 12 cylinder engines made and raced were 4.5L capacity ( the 908 had a cylinder size of 375cc ) X 8 = 3,000cc & X 12 = 4,500cc 

 

This new 12 cylinder engine was" not" chain driven double over head cam , but gear driven ( Cog Wheel )through the centre of the engine , this was a masterpiece of design , it gave the following advantages ]

 

A ) The robust straight cut gear in the centre of the crankshaft was the focal point , on either side of this centre drive gear there were the start of the cog wheel sets( set either side) that went out to either twin cam cam box to drive all 4 cams, this reduced the twist in the cams as they were driven from the centre and could be made a lot lighter ( hollow )

 

B ) Directly below the centre of crank drive gear was the corresponding gear the was driving the shaft ( made of Titanium ) to the rear of the engine , this drove the flywheel ( below the crankshaft line )inside the crankcase , it completely solved ( What Would of been ) the large amplitude scale of the crankshaft vibration , by having the power take off in the centre of the crank there was little or no crank twist ( genius)

 

C ) Directly on top of the crankshaft drive gear was the corresponding gear that drove the top lay shaft ( within the crankcase ) this drove the two massive 12 electrode outlet ignition distributors , like the 908 (8 cyl) engine this 12 cylinder engine had 2 spark plugs per cylinder ( 24 plugs )

This shaft also went external to drive the alternator & in the centre of the engine driven by this top layshaft there was a bevel drive gear set to drive the large cooling ( air ) fan that was laying flat on top of the engine 

 

D ) The freeing up of each end of the crankshaft , meaning there was nothing there at all , no drive pulleys like there would be on a road car engine , this meant for the first time , the engine oil pressure could be feed in axially , that meant as the oil pressure entered the crank it stayed at that pressure even at high RPM to feed the ultra important con-rod bearings ( big ends )

This design was so good Hans Mezger( Porsche engine designer) calculated that the 12 cylinder engine required just 34psi at 10,400RPM to feed the con-rod bearings , compared to 100psi for the 908  and 70psi for the air-cooled 911 engine at 9000RPM

 

Fuel injection , like on the 908 was Bosch mechanical ( MFI ) looks like a diesel pump , not to be confused with the later K-jet used on road cars 

 

The 12 cylinder 917 sports cars / race car won the 24hour  Le Mans twice and because change in capacity just required different size air cooled seperate cylinders/pistons & a different crank if needed , Porsche changed capacity from the 908 cylinders = 4,500cc = 580HP at 8,400RPM   ( first version )

 

2nd version   4,907cc  ( known as the 5.0L ) = 600HP 

 

3rd version  5 474cc ( known as the 5.4L ) in turbo changed form ( 1973  917/30 ) = 1,100 + HP for the Can Am racing ( USA/Canada)

 

Running parallel to all the above , in 1969 Porsche was interested in customers of theirs who were competing in the mega HP racing known as Can Am in the USA & Canada , this is where Bruce McLaren was racing his famous race cars with 750 - 800HP and Porsche entered the NA 5.0L 917 ( 12 cyl) and the 917 just could not keep up in these sprint races , so something had to be done 

Remember in 1969 Turbo Charging 4 stroke engines was in its early infantcy so the traditional method is just more engine capacity 

 

Enter the Porsche 16 Cylinder engine ( engine type 917 ) , this was the logical extension of the 3.0L 8 cylinder & the 12 cylinder engine 

 

All the cylinder heads & cylinders & pistons were straight off the shelf ( race department spare parts shelf)from the 8 & 12 cylinder engines 

 

What had to be made are the new 16 cylinder crankcase & twin can cam boxes in magnesium , new 16 cylinder crankshafts , the con-rods were standard 12 cylinder titanium con-rods 

New camshafts had to be made , along with new longer layshafts ( internal)

All the internal oil pumps & scavenge pumps were from the 12 cylinder

The centre drive ( cogwheel ) gear sets were the 12 cylinder ones

All the special titanium nuts & bolts were straight from the 12 cylinder engine , same goes for the internal bearings

Two massive 16 electrode Bosch distributors were fitted } yes 32 spark plugs 

 

Two 908 ( 3 litre ) 8 cylinder Bosch MFI fuel injection pumps were used

32 spark plugs & 32 spark plug leads 

64 valve springs ( 2 per valve )  & 128 valve collets , and thats with just 2 valves per cylinder , it would be double that if it was 4 valve per cylinder

 

3 or 4 engines were made and tested }

 

5,992cc ( 6L )   = 770HP 

6,543cc ( 6.5L ) = 800HP

6,665cc ( 6.7L ) = 840HP

7,166cc ( 7.2L ) = 880HP

 

Lots of track testing was done , but in the Porsche 917PA Spyder ( Can Am) race car , but the shear length ( size ) of the engine was causing handling issues , but to be fair to the car, it never received the later downforce  wings that the 1973 917/30 received 

 

By the end of 1970 the breakthroughs were coming in regards to another parallel Porsche program in turning the 12 cylinder engine into a turbo charged engine , it became clear to Porsche that the end of the road had come for the 16 cylinder engine , it never competed , it was reported to have been very reliable with lots of testing , but with Porsche seeing 850-950 HP rising to 1100HP for the 12 cylinder 917/30 engine , the 16 cylinder 917PA Spyder went straight to the Porsche museum , where its still there today 

 

Google up } Porsche 16 cylinder 917 engine , its looks amazing 

 

This was Porsche's most interesting era 

 

Regards

Bruce Buchanan

Buchanan Automotive

     

 

[tazzieman]

Having rewatched the CanAm Thunder DVD again last week (stimulated by seeing the McLaren M8 at the Baskerville Historics meet ), this is a great summary Bruce, cheers. 
The cost of E-racing should theoretically be minimal compared to the cost of keeping these Porsches going back in the day!

If only they'd bring a 917 down to Tassy. I wonder if the museum racers are due another world tour?

[ANF]

[Timm]

Love this beast, saw the engine on display when I visited the Porsche museum 10 or so years ago.

[tazzieman]

How much to replace a cracked distributor cap?

[ANF]

How much to replace a cracked distributor cap?

It's a very rare Porsche, so naturally cheap 

 

 

[Spectre]

How much to replace a cracked distributor cap?

Gold....

Cheap if you ship to a US address

[brian in buddina]

Beautiful stuff Bruce, thank you for writting up.

Didn't someone in Australia build a 917 flat 12 out of 2 flat 6 911 motors?

[Peter M]

This was Porsche's most interesting era      

 

Bruce and others,

I agree and can highly recommend Peter Falk's book.  Great pictures, stories and some good insights into some of the big names, both drivers and Porsche luminaries of the time from a man in the thick of it at the time.

https://www.amazon.com/Peter-Falk-Porsche-Rennsport-Development/dp/3927458872

I'm also interested in Mezger's book "Porsche and Me" but the cheapest English language editions seems around a grand so have consoled myself with looking at the pictures and diagrams in the German language version I picked up off ebay for 75 bucks!

https://www.amazon.com/Porsche-Me-Mezger-Peter-Morgan/dp/1906712085/ref=sr_1_fkmr0_1?s=books&ie=UTF8&qid=1506906473&sr=1-1-fkmr0&keywords=metzger+porsche+and+me

 

[brian in buddina]

too bad thay are not available as an E book/download. they would end up selling at lot more.

[michel]

Beautiful stuff Bruce, thank you for writting up.

Didn't someone in Australia build a 917 flat 12 out of 2 flat 6 911 motors?

yes and some 8's

there is was a guy on Alfa BB who had started a flat 8 project using Sud blocks 7 or so years back 

[Buchanan Automotive]

Hi Brian & Michel , you can not make a 917 engine by joining two 911 engines end on end , it might be a flat 12 but way way too long & it has little or nothing in common with a 917 , the 917 engine is DOHC/twin cam per bank & hollow cams with no rocker shafts where as the 911 engine has a single heavy solid cam & timing chains with heavy rockers & shafts ( much heavier )  compared to the 917 engine that has gear driven cogwheels ( straight cut gear wheels ) from the center drive with a separate lower takeoff shaft to drive the off center flywheel , meaning the flywheel & clutch is "Below " the crankshaft at the rear of engine ( quite unusual & not a 911 thing )

Note }  The 12 cylinder & 16 cylinder 917 engine's had ( as mentioned above ) Center Drive from the crankshaft( big straight cut gear in the middle of crank ) , this gets rid of a massive proportion of crankshaft flex that a normal V12 would have , meaning if you had the power take off at the end of  a long 12 cylinder crank( like road cars do ) , you get twist of the crank in racing conditions , this twist is not ideal , so if its a dedicated racing V12 engine then you have to build in extra strength ( thicker & heavier ) crankshaft to try to combat this & everything that goes along with this heavier than desired crankshaft , so the 917 12 cylinder & 16 Cylinder engines respective crankshafts were lighter because of the "Center Drive"  take off

Note 2 }  Crankshaft flexing will & does cause crankshaft breakage , naturally this is exasperated under racing conditions , but even under road conditions they will break if the flexing is bad enough , so this is why lots of road cars ( V8's etc ) have harmonic balance's attached to the front of the crank to try to reduce this very destructive harmonic twisting of the crank

The 917 engine ( internal engine code 912 )  & the 917 16 cylinder engine ( internal engine code 917 ) were actually 180 degree V12 & 180 degree V 16 engines , meaning they were not Boxer engines .   The flat 6   911 engine or the flat 8    908 race engines has one crank journal per con-rod/ piston & these were "Boxer"engines  , where as a 180 degree V12 ( 917 ) etc has 2 ( TWO ) con-rods per / pistons per crank journal ,  this more common( American V8) crank  journal arrangement ( 2) rods per crank journal means the engine overall length can be shortened ( much more compact ) 

In fact the first road going Porsche engine made by Porsche ( for road cars with this more compact ) 2 con-rods per one crank journal was the 928 V8 engine , so the 928 V8 engine( in this area)  has more in common with this more compact design than the air cooled 911 engine , thats because all the air/oil cooled 911 engines were the true "Boxer" engine design of one crank journal per one con rod  the overriding problem with one crank journal per con rod is the engines are longer than need be , so with a 12 cylinder engine it was imperative that Porsche kept the engine length to the absolute minimum & the more modern 180 degree V12 crank design was the only answer , so there is one massive difference why joining two 911 engines together is NOT a 917 engine
By making the 917 engine shorter = compact as possible + lighter still + less flex + less frictional forces , meaning it needed less crank main bearings by being a 180 degree V12 & the very important centre of engine power take off , meaning where the lower internal shaft ( made from Titanium ) would drive the flywheel ,made it possible to rid the engine of the difficulties caused by the natural vibration of the crankshaft , difficulties which increase with the length of the crankshaft 

Even the 917 crankshaft material was quite different to production Porsche cars of the time , the 917 crankshaft is made from chrome-nickel steel (17 Cr Ni Mo 6 ) & has to be case hardened as well for the centre drive gear  , where as the production Porsche engines of that time ( 1968/1969)  were made from heat treated steel & tufftrided where as the earlier 911 engines crankshafts were made from the much more expensive Chrome-Molybdenum steel ( 42Cr Mo 4 )  , so even what the cranks were made from is very very different let alone the difference in length , meaning the 180 degree V12 crank is less than twice the length of X 2     911    6 cylinder cranks

917 Con-rods & conrod bolts are made from Titanium 

917 4.5L ( original version ) used Cromal Cylinders & Forged race pistons  ,Cromal cylinders are forged from aluminum alloy ,machined and then coated with a chrome sliding layer , small holes are rolled into the chrome layer to absorb oil & thus improve the sliding properties ( this was before Nikalasil etc ) .

 When written in 1969 the following literature states } Air Cooled Porsche engines have three types of cylinders & corresponding pistons , The 2.2L 125hp production engine 911T uses cast iron cylinders , the 155hp & 180 hp 911 production engines use so called Biral cylinders , which consists of a cast iron cylinder barrel around which aluminum is cast in a die casting process 

The Engine internal drive shaft from the center drive is made in Titanium

The Lubrication system to the very important con-rod bearings is from nose feed or referred to as axial feed , where as all Porsche production engines have to put up with the common radial feed 

The 917 Cylinder heads are used only on the 908   8 cylinder engine & the 917 engine ( including the 16 cylinder version ) , these have nothing at all in common with the 911 cylinder heads 

The 917 Magnesium crankcase is made just for the 917 engine , its not two 911 crankcases joined in some way ( not possible ) as they needed more internal shafts & a completely different internal layout 

The 917 engine oil pump/s are unique to the 917 engine , that include the oil scavenge pumps in the ends of the ( lower ) twin cam housings

The 917 bevel drive to the engine cooling fan is unique to the 917 , along with the size & shape of the fan assembly 

There are hundreds of other differences but as you can see , different engine's were made for specific purposes & the 917  12 cylinder was made to last at very high RPM in racing conditions for at least for the duration of the grueling 24 hour Le Mans race event , doing it any other way would of been a failure , even Enzo Ferrari when he heard that Porsche was building a 12 cylinder air / oil cooled  race car engine he was reputed to have said it will never work , but as we now know to make it work Porsche at the time invested a massive amount of time & money into the 917 project & if it failed and it could of easily failed , it would have been very costly for Porsche , but they pulled it off 

The 917   Project was Porsche's  race to the moon ( NASA  & the Soviets space race ) equivalent

Regards

Bruce Buchanan  
Buchanan Automotive       40 + years working on Porsche cars 

 

 

[brian in buddina]

Thanks Bruce.

A picture is worth a thousand words, here's a million.

http://www.pbase.com/917carl/917_12_cyl_engine&page=1

[Classic Wheels Australia]

Beautiful stuff Bruce, thank you for writting up.

Didn't someone in Australia build a 917 flat 12 out of 2 flat 6 911 motors?

Hi Brian and all,

There is a clever fellow in Victoria who assembled his own flat 12 engine using two 911 engines for a 917 he built himself.

Not a real 917 12 cylinder but whos complaining when you have flat 12!

Also, there is or was a company called Kraftwerks I believe building 917 replicas in country Vic.

Seeing the frame/chassis of the 917 on pbase is quite staggering.

The average bicycle frame appears heavier.

Thanks to Bruce Buchanan,  your knowlwdge with such detail is amazing.

The small details are the most interseting.

Cheers,

Cameron Smith

Classic Wheels Australia

 

 

 

[brian in buddina]

Thanks Cameron @Classic Wheels Australia 

A very clever fellow in Victora indeed! It would be interesting to find out more about this Victorian double 6. The more Bruce details the development & challenges of 917 it makes you appreciate what this clever fellow was up against. Does anyone know anything more on this project?

Brian

[Buchanan Automotive]

Hi Brian , thanks for the link to the 917 12 cylinder  engine photo's , at first I didn't know what to do with that link , but Sean showed me this morning , those photos are very informative because of the detail one can see in them

[333pg333]

Great thread Bruce! Wow...wonder how much the crank in the V16 weighed?? Must have been massive!