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Buchanan Automotive

50th Anniversary for the 908 ( 8 Cylinder Porsche engine )

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50 years ago (1968 ) was the debut of the 2nd generation 8 cylinder Porsche engine , the 908 , 3 litre eight cylinder chain driven double overhead cam per bank with two valves per cylinder & this engine was quite different to the first generation 8 cylinder Porsche engine the type 753 ( 1.5 L  8 cyl ) & the same engine with more capacity the 771( 2.0L 8 cyl)  &  771/1  ( 2.2L 8 cyl )

But first a quick look at the first 8 cylinder engine was the type 753 , it was a 1.5L( 1500cc) flat 8 (2 valve DOHC ) engine designed to go into Porsche's only ever "pure" Formula One car in 1962  ( car type 804 ) , it only raced a few Formula One races in 1962 & it even won the French Formula One race & that was the only time , Porsche withdrew from Formula One to concentrate on sports car racing

Whats technically interesting about this 8 cylinder engine was the way it drove its DOHC ( double overhead camshafts ) via bevel drive shafts ( a bit like a 1960's/1970's Ducati motor cycle engine )& similar to Porsche's 4 cylinder Carrera "Fuhrmann " DOHC engines , so this means it was very time consuming to make & to get everything to stay together , everything had to be shimmed to get the correct preloads for the multiple bevel drive gears & their respective bearings & expected preloads & clearances ( cold & hot ), so there was a lay shaft driven by the crankshaft and this layshaft in the crankcase also drive the two ignition distributors & the crane drive ( take off ) for the large top mounted cooling fan , from this intermediate shaft ( centre / top of engine crankcase ) two of the bevel drive shafts went off at 90 degrees to the centre of the cam boxes to drive the inlet cams ( L & R ) with their respective bevel gears . shims / bearings & then from the inlet cams & going off al another 90 degrees , but this time straight down are two more bevel drive shafts going to the exhaust cams with their respective bevel gears / bearings / shims 

Magnificently complicated , but durable if all the clearances & preloads are massively time consumingly done

This above 8 cylinder engine ( one year only raced as a 1.5L ) was modified over the next few years for use in sports car racing & had grown to 2.0L with mechanical fuel injection ( engine type 771 ) & then later as a 2.2 L engine ( engine type 771/1 ) , these 8 cylinder Porsche engines were used in sports car & hill climb & Targa Florio competitions & were very successful in Porsche car Types = 718 , 904 , 906 , 909 , 910 ,  One of the standouts for me is the  1967 Porsche 910/8 Bergspyder , this Porsche ( Hill climb special ) weighed in at 410KG( Total car weight) its 1,981cc 8 cylinder NA engine gave 270HP at 9,000RPM 

So these beautifully complicated 8 cylinder Porsche engines competed and won numerous sports car / hill climb events from 1962 to 1968 , the last hurrah for this engine was victory in the 1968 Sebring 12 hour & the Targa Florio in a Porsche 907 & then off to the Porsche museum for this engine & the last Porsche engine to use the bevel / shaft drive DOHC

In 1968 ( 50 years ago ) came the 2nd new 8 cylinder Porsche engine , the 3.0 Litre 908 engine type 300HP to 360HP  in NA form , this was the a simpler chain drive to the DOHC ( much less expensive to make as compared to the type 771 ) and being air oil cooled it was still only 2 valves per cylinder , this engine went on being used in competition right up where this engine was eventually turbo charged ( like its big brother the 12 cylinder 917 engine ) which kept its ability to keep competing in events for years & years , a de tuned version of this 3.0L 8 Cylinder engine was installed into 2 separate Porsche 914's for evaluation purposes .    One 914/8 was built for Porsche's chief technician at the time Ferdinand Piech ( this one was not street registered as the engine was full race trim ), the other 914/8 was given to Dr Ferry Porsche for his 60th Birthday , this was more suitable for road conditions and was fitted with carby's & air-filters and produced 260HP 

The intesting thing about the 908 ,8 cylinder engine was it was a much simpler engine( more cost effective to produce ) as opposed to the previous very complicated first generation 8 cylinder engine ( type 753 / 771 ) that was only ever going to be a very low volume race engine .

The 908  8 cylinder chain drive, twin cam per bank engine was much more aligned with other Porsche road engines in relative simplicity , what I mean they is its not as simple as a VW beetle push rod engine , but its a whole lot simpler than the first generation bevel drive 8 cylinder engines to produce & maintain , so much so ( as mentioned above ) the 908 , 8 cylinder engine was installed in two Porsche  914 road cars in 1969 , and of course because the 908 engine had the more common / much less expensive to manufacture "road car" crankshaft oiling ( pressure" delivery system to the con-rod bearings ) radial feed & being that the 908 engine was a true "Flat Eight" boxer engine , meaning one dedicated crank journal per con-rod , which made the crankshaft a bit longer than it needed to be & made oil pressure supply to the centre of the crank a bit more difficult with its "road like" radial feed crank design , and to keep the con rod bearings from destroying them selves at high engine RPM the engine required massive oil pressure & naturally this means a very high viscosity engine oil to keep the oil pressure sufficient , where as its ( one year later ) big brother 917 12 cylinder engine was a true no expense spared race engine with a dedicated axial feed crankshaft & a more modern & compact 2 con-rods per crank journal making the 917 engine a 180 deg V 12 &  " Not" a boxer engine like the road going 911 engine or the 908 engine 

Here are some notes written by Hans Mezger ( the designer of quite a few Porsche race engines including the famous 12 cylinder 917 engine }
 
Because the 911 air/oil cooled engine used for road and competition had Radial feed into the crankshaft to the  con-rod bearings , the Oil Pressure needed at 9,000RPM was 70 Lbs Sq " ( 5kp/cm/2)  MIN pressure at max racing oil temp ( thats high but necessary because of centrifugal forces)
 
The 908 ( 8 cylinder ) 3.0L air/oil cooled race engine had Radial feed to the con-rod bearings , to overcome con-rod bearing issues in racing the crankshaft required at 9,000RPM was 100 Lbs Sq " ( 7 Kp/cm/2 ) Min oil pressure at Max racing oil temp ( Thats Massive Oil Pressure , but necessary because of centrifugal forces ) 
 
Hence why proper race engines like the 917, 12 cylinder engine had Axial feed & with axial feed there are NO centrifugal forces pushing away the oil trying to get into the crank , so with Axial feed the 917 engine only required at 10,300 RPM was 34Lbs Sq " ( 2.3 Kp/cm/2 ) Oil pressure , thats quite low , but all thats needed because centrifugal forces were not effecting the oil pressure 
 



Regards
Bruce Buchanan
Buchanan Automotive 

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Some things on the bucket list aren't going to happen. ***Sigh***

Glorious engine.

Makes you realise what a utterly boring mechanical age we are entering.

I bought this today

https://www.nytimes.com/2016/12/05/books/revenge-of-analog-david-sax.html

 

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Careful, the machines are keeping record. David Sax aka John Connor. 😉

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4 hours ago, firstone said:

Careful, the machines are keeping record. David Sax aka John Connor. 😉

Scissors , paper, rock. Them machines don't stand a chance. 

OdhGBXR.jpg

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16 minutes ago, Troubleshooter said:

That available on E-Book?:ph34r::Chuckle2:

What's an e-book? Some sort of native bird?

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4 hours ago, Troubleshooter said:

That available on E-Book?:ph34r::Chuckle2:

yes, available in Kindle format - kind of ironic me thinks....

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On 01/04/2018 at 1:31 PM, Buchanan Automotive said:

The interesting thing about the 908 ,8 cylinder engine was it was a much simpler engine( more cost effective to produce ) as opposed to the previous very complicated first generation 8 cylinder engine ( type 753 / 771 ) that was only ever going to be a very low volume race engine .

The 908  8 cylinder chain drive, twin cam per bank engine was much more aligned with other Porsche road engines in relative simplicity , what I mean they is its not as simple as a VW beetle push rod engine , but its a whole lot simpler than the first generation bevel drive 8 cylinder engines to produce & maintain , so much so ( as mentioned above ) the 908 , 8 cylinder engine was installed in two Porsche  914 road cars in 1969 

"Described by driver Gerard Larrouse as "not really a racing engine at all"

"A constraint on its design was that Ferry Porsche asked that it not be unsuitable for use in a production car. His nephew Ferdinand Piech would indeed propose production cars using it" - KLudvigsen

It took several changes of firing order to give of its best

Must be time for some sound!

 

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