High oil/crankcase pressure?

[e170drvr]

Guys, I have an 87 930 with the usual mods. The motor has 100k miles on it now, and I am now thinking about a rebuild. The motor seems to have normal oil consumption, no smoke at all, even startup, and usually just 1 drop of oil coming from the case seam. The car seems to have good power, and the leakdown numbers were sub 6 percent last time I did a leakdown about a year and a half ago. My oil pressure is a hair over 1 bar at idle, however it does not follow the 1 bar per thousand RPM rule all the way up it will sit a little below 4 bar at 2800 rpm, and will sometimes go close to 5 bar when I get on it hard. Does this sound like my oil pressure is too high? What kind of pressures are you guys seeing? I ask because another user brought up the issue of high crankcase pressure in another thread. Maybe this is my clue that I should go ahead and rebuild even though the motor seems healthy otherwise. What are the signs of high crankcase pressure? And should you rebuild just because the motor has 100k on it. Any insight you guys may have would be greatly appreciated.

Eric

[Speedy Squirrel]

Oil pressure and crankcase pressure are two different things. Crankcase pressure is the air pressure in the crankcase. It increases above atmospheric because of pressure blowing by the piston rings. Blowby is normal and the vent hoses on top of the engine and in the oil reservoir vent this pressure to the air inlet.

High crankcase pressure means something is wrong with the vent hoses, or the piston rings/cylinder interface.

High oil pressure doesn't mean $&* unless the person says what the oil temperature is when they measure the pressure.

[e170drvr]

Oops, forgot to mention that. Measured with car at normal operating temp. Oil temp rarely gets above the 8 o'clock postion even on a hot summer day. So how would one determine if they are getting high crankcase pressure, if the oil pressure gauge has nothing to do with it? lots of leakage, oil in intake, maybe, could you feel it with your hand over the oil filler maybe?
Thanks,
Eric

[WERK I]

If your leakdown tests indicate less than 6%, then the only way crankcase pressures can go up is blocked or plugged crankcase/tank vents.
Your oil pressure observations seem to point to someone adding the oil restrictors to the oil line fittings to the camshaft towers. Do search and you will be overwhelmed by the fierce debate for/against them. You decide.
You also didn't mention what brand/type of oil you are using. How does the oil pressure gauge look while the car has been driven for an hour?

[e170drvr]

Thanks Dave, Kendall 20w50 southern Indiana. I rarely drive it less than an hour so pretty consistant once warm. Will look into the restrictors. Given the mileage could it also be clogged spray bars? suppose I would have other problems if it were.
Eric

[WERK I]

Doubt clogged spray bars......it makes a noise from the dry lobes and rockers that is hard to ignore.
I've seen some oils foam more on dry sump systems than on wet sump. I'm using Valvoline VR-1 20-50W and it has cut the foaming to a minimum. Plus it has more anti-wear additives than others. Synthetics cut it to zero, but I'm still looking for another good one besides the Mobil 1 V-Twin Synthetic.