ptuomov

If you can route the oil literally from the nose at the crank centerline, you need virtually no oil pressure. If you can feed it in from a low-radius circle at the nose, say 1/2" from the centerline fronm a 1" diameter nose and if the oil is not aerated since it comes from a dry sum, at 7000 rpm you'd only need 10 psi to supply pressure. So I agree with you that the nose oiling of the crank would be the ultimate solution (both in terms of performance and expense...)

ptuomov

I have only split one 928 crankcase in my life, so I have no experience with this stuff whatsoever. Everybody should heavily discount my speculations.

My immediate (and possibly incorrect) reaction is that load is equal to the pressure times the area. If the passages are larger, then the load increases. You should by this logic see a bigger problem near big passages and opening up the passages should make the problem worse.

Could it be that the damage you are seeing is from detonation shocks? It may be that 2/6 detonate more, for example.

mark kibort

There are consequences of running higher pressure. We had a corvette LS7 powered camaro, that was running too much oil pressure. with more pressure, you get more volume, and what it did was run the drysump dry and it got into oil starvation because the recovery couldnt keep up with the flow. They lost a weekend out of the problem,but are addressing it. It was puking oil out of the breather and oil pressure would momentarily drop. all tricky issues, and just glad I dont have to deal with any of them. you get it wrong and you lose a motor.

jpitman2

How do you distinguish between blackening due to to separation, and due to oil wicking out into microscopic gaps? Can you detect any other signs of the girdle moving relative to the block? The reason I asked about bolts is that waisted bolts/studs can allow one part to squirm on the other under load , but tightly fitted bolts can reduce this. The last variant of the BOP 215 from Rover (4.6L) had cross bolted main caps (block skirt goes below cranck centre), and the main caps (steel) are press fitted to improve location.
Also, if you pipe oil into the crank centre, you can reach the front main and 1/5 big end easily with little pressure loss, but after that, how are you going to reach the next main, with centrifugal force to get oil back from the big end to the next main, and so on.

think about this - how much pressure does it take to split a pissy piece of steel brake tubing - LOTS - I would guess there is 1000psi in there under load. Hopw often do the crimped alloy oil coolers burst at 70 psi? I use 1/16" ID nylon tubing in my models, hand pushed onto barbed fittings, and 100psi wont blow them off - .003 sq" x 100psi = 0.3 lb force.
jp 83 Euro S AT 52k

Lizard928

Tuomo,

I can say for certain that most of these motors had no detonation going on in them. My initial reaction was similar to yours in that the larger passages with greater surface area should have experienced more of a problem instead of less. However I feel that the reason for this is that the smaller channels are actually seeing a build up of pressure, higher than the larger ports where there is less restriction. The larger port also supplies oil to the head and that therefor reduces the actual pressure that channel sees.

Of course, like you I am a mere amateur and I could be completely wrong. Like everyone else, it wouldnt be the first time, nor will it be the last. But I am not one to just sit on the fence and speculate, we have enough doing that. I would rather jump in with both feet and do what I think will solve the problem.
Worst case I will spin some bearings and have to redo the bottom end. I am using stock parts so wont be out tons if it does let go. And the next time as I said, I would do a snout fed oiling system. I do however have some nice 18x11 medium soft slicks ready to push the envelope.

I will still plan on replacing the rod bearings at least once a season. And I also have gotten a reasonably accurate oil pressure gauge that is good up until 110PSI.

Lizard928

JPitman,

Having worked with hydraulics and seen probably millions of pumps, and other systems, I can say that there is a very obvious difference between the two. Especially in aluminum.

danglerb

Good to know the relief is 9 bar, but that makes me want a sender that reads 10 bar or so to see whats really going on.

ptuomov

Once you get the oil to the centerline with some small static pressure and/or flow, you're good. Yes, once the oil makes it to the rod journal, you need more pressure to push the oil back to the inner circles, closer to the centerline. But you automatically have more pressure on the outer circles, which will do it. It's very much analogous to water flowing just fine in a pipe that has a lot of altitude variation. In other words, nose oiling works great in terms of requiring a very low supply pressure.

(As an aside, as long as the leak from the bearings is controlled as designed, the pressure in the crankshaft oil passages is about the initial supply pressure plus 1/2*rho*omega^2*r^2, where rho is the density of oil (about 886 kg/m^3 at 100C), omega is the crankshaft rotation speed in radians/second, and r is the distance of that specific part of the passage from the crank centerline in meters.)

That's because the area is very important. Greater the area, greater the force. If the pipe has a large diameter, there will be a large force pulling the pipe apart in the direction of the pipe circle tangent. That's why large diameter pipes have to have much thicker walls than small diameter pipes to handle the same pressure.

WallyP

Years ago, Porsche had major oiling problems with some of their flat racing engines - they couldn't make them live, even with very high oil pressures. They went with snout feed, and the engines lived at 18 psig oil pressure.

etiennekuh

I have a quick question. I have a 82 4.5 euro 928. I am mesuring at the oil pressure sender 16 bar of oil pressure at idle and when the rpms rise the oil pressure keeps rising. I cleaned the oil pressere valve, but it didn't help. what could this be?

etienne

76FJ55

16 Bar is way high. what are you using to measure it, and where? Usually at hot idle the pressure relief valve is closed anyway so double that is your problem. What oil and weight are you running?

Lizard928

I think he means 16 PSI not BAR.

Which would be about right.

etiennekuh

I now measured again with a different gauge. It's now 8 BAR. When the car warms up the pressure drops till 2 bar so thats ok. but when I push the throttle and lett the rpms rise till 4000 the pressure rises till 8 bar, and then the driversite camshaft seal pops out. so the pressure is still to high ( I am messuring at the oil pressure sender)

Etienne

Vilhuer

8 bar is just right. On later 32V it should be 8.5 bar. Gauge only goes to 5.

etiennekuh

But why does the camshaft seal keeps popping out? and what if the pressure becomes more then 8 bar, when you let the rpms rise till the next shift (say 6000 rpms (it's a automatic))?