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Bar - What is the running BAR for a 1980 931?

 
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Rick MacLaren  
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PostPosted: Sat May 11, 2002 1:29 am    Post subject: Reply with quote

At idle, mine is about 3 or 4, and under about 7 PSI it is about 5, at full boost it is higher, at 7 or so, and it was a little worrying. What's the right pressure?

Summary

Idle 3.5
7 PSI 5
10 PSI 7 up

Worrywart.
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Smoothie  
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PostPosted: Sat May 11, 2002 1:55 pm    Post subject: Reply with quote

I consider oil pressure to be tied to engine speed, not boost pressure. My '82 931 usually shows about 2 bar at 1000 rpm shortly after start-up, 4 bar at 2000 rpm, 6 bar at 3000... It varies with engine temp - pressure drops some as the engine warms up.
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Rick MacLaren  
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PostPosted: Tue May 14, 2002 6:13 am    Post subject: Reply with quote

Sure, as long as they're not inverse relationships we should be dealing with roughly the same trend. I notice that yours goes to 6 bar at 3000 RPM. So boost my pressure of 1/2 boost showing 5 bar isn't out of whack. What's the ceiling, the highest you've seen, at whatever RPM?
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Smoothie  
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PostPosted: Tue May 14, 2002 12:13 pm    Post subject: Reply with quote

I just got a couple surprises today with the oil pressure. I was waiting in line for inspection and the oil light flashed a few times; the gauge was in agreement and reading low. I revved it a bit and it came up, then settled back, but the oil light didn't come on anymore. When I got the car back after inspection it was still reading low so I pulled over to check the oil. It was within the correct range, but I added a quart anyway. Still read lower than usual, but it was getting up to 3-4 bar at around 3k-4k rpm while driving. I got back home where it was parked for a while, then the next time I started it, it was reading higher than usual - like 5-6 bar at low rpm. I don't know, maybe that pressure valve in the oil pump flaked out temporarily. (I hope)

Anyway, I can't really say how high the pressure has been on my car - I'm usually looking places other than the oil pressure gauge while my rpms are around 4000 and above. I'll try to get in a few more looks at it though and let you know what I find
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John H  
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PostPosted: Tue May 14, 2002 3:20 pm    Post subject: Reply with quote

I've seen the oil pressure on my car at 8 bar when cold.
Normally it runs at between 4 and 6 bar.
When racing it drops to 4 bar at 6000rpm after around about 15 20 minutes of racing.At the end at idle it's normal just on 2 bar.
I've an adjustable pressure switch set to come on at 3.5 bar and as soon as it hits that whiel racing I back off and see what's happening. Only happended once and this was due to racing on a street circuit (concrete walls both sides and no wind) in the middle of summer and tailgating a 911. Once I was back into fresh air the pressure went back up to 4+ bar.
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Smoothie  
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PostPosted: Wed May 15, 2002 4:51 am    Post subject: Reply with quote

I did a couple of accelerations to above 5k rpm today and the oil pressure peaked every time at just under 6 bar. This after driving a few miles and the engine warmed up.

I might have been just scaring myself yesterday with those low pressure readings as it was rainy and I had my headlights on. Duh. I should have either added 1 bar to the gauge readings or shut off the headlights.
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Rick MacLaren  
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PostPosted: Wed May 15, 2002 4:58 am    Post subject: Reply with quote

Ok thank you! These numbers are looking more like the numbers I saw on mine. I think 7 or 8 bar when cold. It levelled off somewhat later as it warmed up. Whew! Just a tad scared after the engine rebuild.

Know what? It's like in the movie Starship Troopers where the teacher says "Something given has no value". If you PAY for your engine rebuild of your Porsche, or even part of it, you're much more careful with it. More willing to drive slow, watch the gauges, and be paranoid for the sake of preserving your investment.
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924RACR  



Joined: 29 Jul 2001
Posts: 8109
Location: Royal Oak, MI, USA

PostPosted: Wed May 15, 2002 6:38 am    Post subject: Reply with quote

Learning that lesson now, are you?

I always thought I had more caution after doing the work, now that I can appreciate the effort.

My first race motor, just a stock motor re-ringed after 138kmi, is starting it's 3rd race season... still pulling strong...

_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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larso  
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PostPosted: Thu May 16, 2002 9:14 am    Post subject: Reply with quote


Up here in the cold north, my gauge pegs to 10 sometimes when it's cold. When it is anywhere under 15 degrees Celsius, and I have 10W40 or 15W40 oil in the car, the gauge will go as high as 8-10 bar. It still goes to 7-8 bar when cold if its plus 20 degrees celsius out. Driving the car around cold with 10 bar can't be good for the engine so I always try and shift before 3000-3500 RPM until oil presure drops and temp comes up.

I find that the oil pressure drops a lot more if you drive the car hard for a few minutes. Even if the coolant temp remains the same, driving the car hard seems to show a drop (about a drop of 0.5 bar compared to what it was when driving easy). Coolant temp is the exact same as before, maybe the oil temp is higher. My guess would be that the oil temp can get higher, but the coolant temp doesn't get affected because the oil takes a while to transfer the heat away. But, even after driving around for 10-20 minutes, this drop will remain. It will only go away if you shut the car off and wait till the engine gets cold again (or going out on teh highway at a constant speed and letting the temp needle go back into the white)

Once the car has been driven hard, the oil temp drops almost permanently...unless I turn the car off and let it cool down all the way, or unless I go on a highway and cruise at about 2000-3000 RPM at a constant speed for about 5 minutes, and then drop to idles a few minutes later.

Would this be a sign that the oil is breaking down? why would the oil cure itself only after getting real cold again? I thought once oil was bad getting cold would not re-incarnate it to good oil.

I am hoping that the oil is not getting very thin and crappy after driving the car hard.

Or could it be that once the oil pressure sensor sees hot oil temps, it decides to screw up for a while until it gets cold
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numbers  
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PostPosted: Fri May 17, 2002 9:37 am    Post subject: Reply with quote

Well Larso, stop running that WalMart special motor oil, and your pressure will probably be right up there.
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Rick MacLaren  
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PostPosted: Sat May 18, 2002 1:48 am    Post subject: Reply with quote

Larso goes to Wallmart? I just thought he emptied the used oil from the cars of stranded motorists and re-used it?
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