Cloud9...68

RS Barn sells an outstanding dual oil cooler set-up. I have it on my track-dedicated 968, and the highest oil temp I see on the hottest Texas day at the track is about 215 degrees F. The second cooler goes where the transmission cooler on Tiptronic cars sits, and the other cooler in the kit replaces the stock cooler (I believe it has slightly larger capacity). The lines fit directly on the flange on the engine. It is a lot of work to install - you have to make your own brackets and shrouds for the coolers - but they make a huge difference.

I also had my crank cross-drilled, installed a Lindsey Racing oil pan baffle, a crank scraper, and had the oil pick-up tube reinforced. It's been about three years since I've rebuilt my engine, with hundreds of track sessions, and no problems so far.

JET951

The below is a post on put on Rennlist a few years ago , the subject was about 944 conrod bearings etc , so quite relevant to the subject at hand }

I do not know if any one has thought of this but the connecting rod bearings like the crankshaft main bearings are never ever designed to make contact with their corresponding metal counterpart , meaning if there is even a fraction of a second contact between the metal surfaces then the slipper bearing in question is now badly damaged ( flatspotted / hammered/ galled ) what ever way you want to put it its damaged and Will Fail very shortly .

But how I hear you ask ?
Answer = lack of oil film strength & or oil pressure at that bearing/s and OR the conrod bolts have stretched ( mechanical overrev / downshift over rev )& with that slight ovality of the conrod journal ( no longer round , but ever so slightly distorted )

Meaning if its the first & most common cause then the first line of defence is oil pressure between the bearing shell & the crank journal , the second line of defence is oil film strength , combined you will have reliability
Note } the above relies in that the said bearings are in excellent condition before being flogged at the track & not already damaged

Now to background info }

A) 944 / 951 / 944S2 / 968 do have a small flaw in their road going crankshaft design , and that tiny flaw shows up at high core temp ( read very high oil temp) and at high RPM , no 2 conrod bearing will starve of oil pressure compared to no's 1 , 3 , 4 ,
The 928 series has the same tiny flaw and its no 2 & 6 conrod bearings ( same journal on crank)
The same period 911 air-cooled engines are similar , they will starve 2 & 5 conrod bearings if insufficient oil pressure is NOT supplied & how do we induce this insufficient oil starvation condition in these last century Porsche engines ?

Answer = Easy , run too low oil viscosity , add high oil temp & Max revs at a track or even road = BOOM , meaning this century engine oils in last century Porsche engines ,like a 5w-40 or a 10w-40 & oil viscosities like a 0w-40 are a disaster waiting to happen . but these low viscosity oils in this century engines are fine , the centuries do not mix

The Flaw is that all the above are road engines and like all road engines they have radially feed oil pressure into the crank to feed the conrod bearings , this means the oil at high engine RPM has to fight against centrifical forces , where as AXIALLY feed oil pressure into the crank ( like the Porsche 917 engine ) sometimes known as nose fed and later Porsche dedicated RACE engines do not have radially feed oil feed , thats just for road cars that pretend to be race engines

How do we get around it ?
Answer = easy just increase oil viscosity up to where the owners manual says so ( for road conditions)
For track , you must increase oil viscosity further & add extra oil film strength , hence why oil companies make racing oils , which by the way are all higher in ZDDP which gives higher oil film strength

B) We have been competing 951's ( 944 turbo's) in either 2.5L single cam engines or 3.0L twin cam ( custom of our design)turbo engines( 440+HP) for years on the race track with NO crank ( connecting rod failures at all ).
With two Drivers Championships and two Motorkahana Championships in the bag along with countless lap records & a heap of customer 944 & 944S2 & 951's with class winning & Championship results with no crank/ connecting failures at all

The reason & answer/ Clue is simple ( its in the owners manual that came with the car )
Oil Viscosity & in turn oil film strength , in other words in the owners manual( oil vis page) it states( for road use of say a 944/ 944S / 944S2 / 951 / 968/ 928, from minus ten deg cel to Unlimited high ambient temps use a 20w-50 engine oil ( shaded look at me section )
This is a last century oil viscosity for a last century engine design , nothing wrong with that at all , its just a fact .

Now the basics }

What is engine oil film strength ?

Answer = The ability of the engine oil to keep metal parts away from each other , like cam lobes from scratching into the hydraulic lifter faces or alloy pistons not galling against the alloy cylinders or the ability to just give that last fraction of a second defence( last line of defence) against lowish oil pressure in no 2 con rod journal / bearing at high RPM with very high oil temps

Hence the reason( in regards to proper racing of last century engines ) of monograde racing oils like Brad Penn SAE 50 wt racing oil for long distance events or the extreme Brad Penn SAE 70 wt oil for drag car engines ( no 5w-40 or 15w-50 ) engine oils here because they( engines) just fall to bits because of lack of oil film strength

How do you increase engine oil film strength on this planet in this universe ?
Answer = two things combined }
1) increase oil viscosity from say 5w-40 to say 20w50 ( instant increase in oil film strength)
2) increase the levels ( up to a point ) of ZDDP anti wear film
combine the both = maximum oil film strength , remove one = lower oil film strength , very basic stuff

Now what we do with our own 951 & customers 951's / 944S2's etc }

For the track , first prepare the car with the following }

A) Sump off and new big end ( con rod bearings ) standard Glyco bearings
If its a turbo with more HP then aftermarket rods & standard Glyco bearings

B) Head off and new valve guides ( twin cam 944S , 944S2 , 968 must have new chain between cams & slipper guides) , providing the chain sprockets are not worn

C) Later type oil thermostat

D) Much larger oil cooler ( optional for NA ) Not an option for Turbo , and when I mean larger I mean three times the size

E) we do not run dry sump or acusump at all , even with the use of slick racing tyres on the track

F) standard oil baffle in sump & standard sump , we do NOT modify the crank or oil pick up one bit

G) custom crankcase ventilation system , so we control the crankcase venting on the track ( important)

H) This is the clincher , higher racing oil viscosity ( as opposed to the road 20w-50 oil vis) , meaning we run 25w-60 Valvoline racing , Minimum viscosity , meaning this is the absolute "minimum" viscosity the 951 should ever hit the track with & the Oil Temp in the crankcase should never ever exceed 120 deg cel & naturally this means a seperate oil temp gauge with its temp sensor in the sump

I) Sump off after every season ( simple to do) and recheck the condition of the conrod ( bigend) bearing shells ( no 2 particularly) and then depending on boost you can increase the checking intervals to say every 18 months

Note } 25 year old "standard" conrods are generally OK for just road use , these days to get a 944S2 , 968 , 951 ready for the track and if the funds are OK , we will install a new set ( 4 ) of good quality aftermarket conrods while the sump & head is off , this completely gets rid of metal fatigue worries at the track & guarantees perfect roundness of the conrod & conrod bearing for the crank journal


This is not rocket science its just a basic understanding of a basic 4 cylinder well designed engine that does not take this century car engine oils ( read low viscosity / low ZDDP/ low oil film strength) well at all & neither should it because it was designed deep into last century when the use of oils like a 20w-50 as an engine oil was the complete norm

Regards
Bruce Buchanan
Buchanan Automotive 40+ years working on Porsche cars

Cloud9...68

Good information. I did a track session yesterday when it hit 106 for a high (was probably just over 100 degrees when I did my session), and the highest oil temp I saw was 209 degrees F. I am using a high viscosity (15W50) oil with high ZDDP content.

JET951

With those high ambient temps( 37 deg cel/100 Fah) a 15w-50 is borderline in a last century Porsche at the track , so much so I would not take the chance , if I had to use a Racing 15W-50 ( low detergent + high ZDDP ) the ambient temp would not be above 15deg cel / 50 Fah & even then I can not see the advantage of excessive risk

Where as a high ZDDP 15w-50 is OK for normal commuting to & from work at low revs in a last century Porsche , but a decent 20w-50 is better

Remember at high RPM in a 944 , 944S ,951 ,944S2 ,968 the only way you can give the con-rod bearings sufficient oil pressure ( particularly No 2 ) is to make sure the oil viscosity is high enough so at higher oil temps ( track temps mainly ) the oil pressure up high enough ( on this planet oil pressure drops as oil gets hotter at the same given RPM )

Basic design & what we face with these engines ( basic understanding )

We already know that the 944 crankshaft ( like all road cars ) is radially oil feed & this compromises oil pressure to the con -rod bearings at high RPM & the higher the RPM the worst ( lower oil pressure ) it gets& at low oil pressure the con rod bearings go metal to metal & that equals = BANG , it only take a milli second at high RPM

Here is some notes written by Hans Mezger back in the late 1960's /early 1970's , Hans as you probably know designed quite a few Porsche race engines

Quote } The oil feeding system of the 917 engine is quite different , it is more efficient because it is almost independent of the engine speed and requires a lower oil pressure , because of the central drive ,the ends of the crankshaft are free & hence oil is fed into the crankshaft Axially from both sides
Hans goes onto explain that they did extensive tests of three crankshafts & how they feed the con-rod bearings with sufficient Oil Pressure at high RPM

For the normal 6 cylinder road & racing 911 engine ( radially fed ) the oil pressure needed to be min of 5 Kp/cm2 ( 70Lbs 2) to provide an adequate oil pressure supply at 9000 RPM

For the 8 cylinder 908 racing engine ( radially fed like the 911 & 944 etc ) the oil pressure needed to be a staggering 7 Kp Cm2 / ( 100Lbs 2) at 9,000 RPM , thats hundred pounds oil pressure ( massive ) = oil temp kept as low as possible and very high oil viscosity is the only band-aid answer

For the 917 12 cylinder racing engine ( axially fed ) , the oil pressure only needed to be 2.4 Kp/Cm2 ( 34 Lbs ) at thats at an engine speed of 10,300 RPM to 10, 500 RPM

The 908 did NOT run on a 15w-50 oil , if it did it would last a few minutes( maybe seconds) at best

Running a 944 , 944S , 944S2 , 951 ( especially ) , 968 at the track & if the ambient air temp is above freezing , then I would only use a high ZDDP low detergent 25w-60 racing oil as the MIN viscosity & I do mean Min Viscosity .

Remember , all last century Porsche engines are just that "Last Century " and they were designed decades before low viscosity so called synthetic engine oils ( like 5w-40 etc ) , the 944 ( all ) 928 ( all ) were designed for the NEW to the late 1960's / early 1970's multi grade 20w-50 engine oils

But on the road a 15w-50 high ZDDP or just about any high quality 20w-50 is fine

Regards
Bruce Buchanan
Buchanan Automotive 40 + years working on Porsche cars