Help Me Diagnose Low Oil Pressure in a 930

[tailwind22]

Moved from the 930 forum due to lack of repsonse. Trying to systematically work through a low oil pressure issue in a 1978 930 highly modified motor with unknown miles (leakdown performed by a reputable Porsche only shop showed rates of#1-7%, #2-5%, #3-10%, #4-6%, #5-8% and #6-6%. Pressure when warmed to 180 degrees is 3 to 3.1 bar @5000 rpm. These are consistent readings before and after 1) changing out the oil pressure sender and 2) swapping out the guage from my 89 Carrera (reads a consistent 4.5 bars on that motor) so I know it is not a guage or sender issue. No rattling or knocking is audible. I was going to go the cam line reducer route but that really seems like making excuses for low oil pressure. I will be cutting the oil filter in the next couple of days to see if there are any tell tale signs of metal particles. I would appreciate educated opinions on the situation. Thanks.

[304065]

Have a look here:

Ultimate Oil Pressure Relief Valve Thread

Have you checked the pistons and springs?

[kodioneill]

45 psi isn't that bad. My Carrera is 3.5 when warm my sc is 4.0.

[twistoffat]

I´m no expert on 930 and their turbos but I read an interesting thread on a German site recently about low pressure on a late 70´s Turbo. Consensus was that 3 bar was not that uncommon but shouldn´t go below that and some had mentioned rear fed oil lines to reduce resistance to centrifugal forces like on racing cars could led to lower oil pressure. Others started going on about oil viscosity on Turbos having an effect on oil pressure up to 1 bar. I´m sure somebody here will chime in maybe to confirm this or possibly to say its incorrect.

[tailwind22]

Originally Posted by twistoffat

I´m no expert on 930 and their turbos but I read an interesting thread on a German site recently about low pressure on a late 70´s Turbo. Consensus was that 3 bar was not that uncommon but shouldn´t go below that and some had mentioned rear fed oil lines to reduce resistance to centrifugal forces like on racing cars could led to lower oil pressure. Others started going on about oil viscosity on Turbos having an effect on oil pressure up to 1 bar. I´m sure somebody here will chime in maybe to confirm this or possibly to say its incorrect.

This is interesting...btw, looking at your avatar I assume you are a road cyclist. My passion also, besides cars.

[tailwind22]

Originally Posted by 304065

Have a look here:

Ultimate Oil Pressure Relief Valve Thread

Have you checked the pistons and springs?

I did a quick look at the article a week or so ago. I am rereading and will dissamble and take a look at spring and piston. Could be something here.

[twistoffat]

Originally Posted by tailwind22

This is interesting...btw, looking at your avatar I assume you are a road cyclist. My passion also, besides cars.

I am indeed and have the scars to prove it.

[spuggy]

Lower pressures on pre-78 930's are normal; they have the same oil pumps as the N/A cars.

78-up 930's use the later 930 pump (which, if the figures I've read are to be believed, pump the most oil of any pump the factory used - the later pumps apparently focus on increasing the scavenge, not the supply, side) make more pressure, in my experience.

I have a '78 930/60 motor in a car with a numbered pressure gauge; for the last 7 years/30,000 miles it has read 120 PSI on cold start, dropping quickly to 100PSI, hot it runs 25-30PSI idle, makes 60PSI at 2000 RPM, and reads ~80 PSI anything over that.

When it started behaving differently recently, I swapped the gauge, replaced the sender (which rattles gently when shaken) and had the pressure relief checked. Haven't driven it yet...