dr bob

Oiling and beathing are discussed on page 11 of this article.

svp928

Earlier in the article, there is a photo of what they call "pvc slots" that vent crankcase gases into the heads. This feature is missing on our engines- the only way I see for crankcase gasses to get into the heads is UP the drain channels--- they discuss the shape and placement of these slots, as well as enlarging the drainbacks, as being critical to getting oil out of the heads...
We need to figure out how to implement this ourselves...

Ra928

\

bu it is easier to clog 2 small holes than 1 large hole

GregBBRD

Post 272.

GregBBRD

Pushrods....

Lizard928

What about 2 (or more) -16 hoses tapped into the cylinder head with a small extension of the hose so that it extends past the 4 normal drainbacks.

This hose could then be tapped back into the oil pan.
The crankcase air rushing through will surely generate a slight amount of pressure, and hopefully push the oil out of the head and down the hose back into the sump. The bottom end of this hose should be as low as possible to try and ensure that it remains in oil at all time. The other benefit to this is that the hose could be coming off the head and go straight down (perpendicular to the ground, maximum gravity). Having the bottom end covered in oil should prevent the hose from acting like a further vent tube allowing the air, and or oil to further travel up the tube.

Keen to hear thoughts on this.

hairywithit

ah, the mustang is DOHC - unless you mean convert the 928 to pushrods LOL


for 931: the guys going uphill want the pickup to be at the rear, but yeah. If you are not going to cut back the flow into the head then additional drains are needed for demanding drivers.

Has anyone made a rear cam plug out of perspex? Seems the easiest way of getting a visual on the oil level -- for the short cam engines natch.

soupcan

Post 160

Lizard928

oops, must have missed that one/page....

depami

???????

Shark_Week

pushing this back to the top. too important. thanks greg for your hard work

GregBBRD

Denny:

I had plenty of time to run all the options through my head and come up with my own solution, long before I posted on this thread, the first time. Right or wrong, I will be back on the dyno, probably next week (need to make sure the dyno shop has an opening), to test.

UncleMaz

Greg, do you need anyone to water your plants? If so, I volunteer.

Shark_Week

i'll mow the lawn!

Louie928

This is a great thread and I check it every few weeks. Lots of recent activity now and I saw the Utube video of some checks I made to try and figure out the oiling problem. Short story--I haven't quite got there yet. Thanks to Tuomo for posting it. This was done about 10 years ago. I have found out a few more things and some of my initial thoughts were wrong. Maybe I can help steer some to a good solution and save someone from wasting a lot of time.

I'm a big fan of Smokey Yunick and you'll find a lot of answers applicable to the 928 in his books. One of my favorites is "Power Secrets". I'll list a few things as I can remember them in no particular order.

1. The 928 engine lubrication system is horribly designed for any high performance use. That it can have any reasonable high performance life is due to ingenuity, patches to cover impossible design flaws, and luck. Or, you can do like the very successful high time racer we know and limit the RPM especially in corners. It's not really the Amsoil. It's the driver.

2. Using the holy cam cover we checked to see just exactly how much oil was being pumped up to the right side cyl head at high RPM. We did this at the old SIR track (near Auburn, WA) during a drag event. Several current 928 owners were there watching. Adam Birnbaum, Tom Middleton, and a few others. Revving the engine to over 6000 to rev limit cutoff showed plain non-aerated, oil splashing around and a small rivlet running rapidly down each drainback hole. It didn't even take 1/4th of the drain back area to easily handle the oil. The amount of oil didn't change above about 2500 rpm. The 928 oil pressure regulator keeps pressure to about 100 psi from around 2500 on up depending on oil temp and viscosity. Oil system oil fed to the head is not too much for the drain back holes and it doesn't change in volume with RPM. There is no point to limit the oil feed to the cams. Don't bother.

3. The normal oil level in the sump is way too close to the crank. It is less than an inch and with a stroker motor less than that. Do not overfill the sump. An over full sump can cause oil to hit the crank even with no vehicle motion. It's a tornado in there. Smokey Yuniks advice was to keep the oil as far away from the crank as physically possible and should be more than 2 inches with 4 inches being better. This is impossible with the 928 low mounted engine and flat sump. The aluminum spacer between the block and sump helps, but is only a band aid. Any sloshing of the oil will cause it to be hit by the rotating assembly and 1) turn to foam, 2) be caught up in the vortex around the crank. The whirling crank is like a centrifugal blower. Low pressure in the center and higher pressure on the outside. When the rods hit the oil the oil goes toward the low pressure center usually near the ends and gets flung to the outside where it hits more oil and the cycle repeats. It is a rotating helix of oil foam. The whirling crank can hold more than a gallon or so of oil in a molasses colored cloud. This can cost maybe 30 hp, heats the oil, and once started, is hard to stop while at high RPM. Crank scrapers are supposed to help control this. A dry sump is one answer, but not usually achievable on a street driven car due to no room for the tank and no available drive for the pumps.

4. I used to think that the frothy oil seen on the uTube video through the holey cam cover window was all oil whipped by the crank and forced up through the drain back holes by crankcase pressure and vented out the cam cover vents. Kevin Johnson had a theory that a lot of the oil foam was coming through the oil system and expanding as it came out the cam bearings. I think he is largely correct except a lot of the foam does get blown up the drainback holes too.

5. Accusump.. It's a good thing and probably does save engines in some instances of oil pressure loss. However, consider this. By the time you have uncovered the oil pump pickup you have foamed your oil in a 928. The accusump may have saved your engine, but now it will be recharged with foamy oil. If the Accusump is mounted vertically with the inlet/outlet at the bottom, and it isn't called upon to discharge for a while, the air in the oil may have separated and you could get a discharge of clean oil. Or you could get a discharge burp of air.

6. Stroker motors with the stock intake manifold are breathing limited and the hp peak is around 5000 RPM, maybe less depending on the cam and valve size. It's fairly safe that the oil won't get to a condition to foam at 5000 or below. Change the intake to a ITB where peak power is 6500 or more and the longer stroke motor will be more likely to foam the oil than a short stroke 5L.

7. Smokey is adamant about providing sufficient crankcase breathing. IIRC, the 6.5L size motors should have a breather tube of at least 1.5" and the 5.0L will be ok with 1". It is really hard to get a 1.5" breather on a 928 anywhere. I use two 3/4" breather tubes to my air/oil separator and a 1" from that to the atmophere. I'm fairly confident I read that a 5.0L motor will normally make about 5 cfm blowby and the 6.5L about 7 cfm blowby. If not vented from the lower part of the crankcase, where does it go? Does it seem too much to conclude that the blowby will simply go up the cyl head oil drainback holes and vent out through the cam cover vents? If you have foamy oil, that brown froth like whipping cream will go right along with it. When the crankcase is properly vented, the foamy oil won't go up the oil drainback holes. It still foams, but doesn't blow up the drainback holes on either side. The key to understanding that the too much oil in the cyl head problem is crankcase pressure, and not so much the rotation of the crank pumping oil up there. It is a factor, but not the only thing. Stock, the 928 32v motors have horrible, pathetic, inadequate, crankcase breathing. Throw it all away. If you want to stay green, (and there is nothing wrong with that) put on an adequate (big as you can fit) crankcase breather, run the vent through a good air/oil separator such as the ProVent, plumb the outlet back to the air intake - not the intake manifold below the throttle. The air/oil separator oil drain can be "T"ed into the oil dipstick tube. It'll work. Otherwise, vent the separator outlet down vertically under the car with the end of the tube cut back at a 45 deg angle. That will provide some small vacuum as you are driving.

8. Cam cover vents. I've always wondered why 928 folks seem to think the cam cover vents need to be used as an outlet vent. The answer is probably obvious if you consider that the crankcase has no reasonable vent and the blowby has to go somewhere. Might as well use the cam cover vents so the blowby can carry a bunch of oil along with it. Not a good plan. Nothing inside the cam cover generates any gases that have to be vented save a bit of exhaust gas escaping past the exhaust valve stem seals and that isn't much if any. The cam cover vents should admit some fresh air. I like to plumb a line from filtered air to one cam cover vent on each side. Use the shield on the inside of the vent to keep oil from splashing into the tube. One cam cover vent makes a good place to have an oil filler if you can't use the original such as with ITB intake or Andy Keel type supercharger intake. You have to enlarge the hole and weld on a small can and have a cover. It works fine to just use an O ring seal on a push on cover. Remember, with a properly vented crankcase there is no pressure inside to blow off a cap, or the oil dipstick.

9. Speaking of crankcase pressure... Next time a 928 is on a dyno of any kind. Take off the oil filler cap and put your hand a few inches from the opening. Do a short run and you'll be amazed at volume and velocity of the blowby coming out. Where does that normally go? Maybe up the oil drain passages? Kind of a scary thing to do.

10. The vented oil filler cap I made works quite well at keeping the crankcase pressure down so no oil is ingested into the intake. If the breather system is otherwise stock there will be a slight vacuum pulled in the crankcase at idle and cruise throttle. That means air will be drawn in through that breather tube. I connect it to the smog pump air filter that is right in front of the oil filler. I don't need the smog pump filter because my smog pumps seem to fall off shortly after I get the car.

11. I don't buy the idea that so much oil gets blown up into the heads that the oil pump runs out of oil. Look at the utube video and you see quite a lot of foamy oil, but it is far from filling the head. The video was taken looking at the exhaust cam so is at the bottom of the cam cover. Even so, it's foam not solid oil. How much beer do you get when drinking foam? Whipped to a froth, there probably isn't more than a cup or two of actual oil. True, it represents some excess oil and it shouldn't be any oil. Fix the crankcase pressure problem and you'll have less, maybe none, foamy oil up there. And for goodness sake don't vent out the cam cover vents. Let fresh air in there. It flushes out combustion byproducts
One more time... Vent the crankcase and you don't blow anything out the cam cover vents.

12. That still doesn't eliminate the foamy oil. It only keeps it from being blown out the vents. I think the oil pressure loss we see in a hard corner come mostly from having too much foam relative to solid oil. I think the 2/6 rod bearing failures come from having too much foam in the oil, not necessarily no oil.

13. That gets back to how to keep from having sloshing oil so close to the crank creating all this foam. Crappy design. Use what band aids you can. I have an idea I want to try, but have no time right now. It involves electric pumps and G switches. You can figure it out. I think it may be the next best thing to a dry sump.

14. Where to vent the crankcase? Up top somewhere. I doubt it matters much. Do something to keep the velocity of exiting the blowby gases as low as possible and that means a big area thing. I use the normal big hole up front where the oil filler is. I make a metal box that fits down inside and is angled on one side to conform to the shape of the hole. The box has louvers, or holes angled so slung oil would not go through as readily as if it was a straight hole. Plenty of holes/louvers. Think keep velocity low. I leave the bottom 1.5" of the box empty to give oil a chance to drain out. The top half of the box has some folded screen or loose copper Brillo pad. The top of the box has a cover bolted to the block where the oil filler fastens. Then a big hole leading to a vent tube, or another box with some maze type passages with right angles then leading out to a big (1"+) outlet tube. You want to make the oil laden blowby take sharp turns so any liquid can't follow the gases out. Liquid will collect and run back inside. That is if the box is big enough to keep velocity down. The outlet of this pre-air/oil separator needs to go to another air/oil separator like a ProVent or a similar home made device.

15. The Utube video was made at Spokane 10 or more years back. Spokane is ideal because of the killer left hand turn at the end of the mile long straight. Worse than at Thunderhill because it is longer and faster. It was run CCW. I had no audio as that would have helped a lot to determine where we were on the track. Mainly, you can see the foam begin to clear up about as soon as we got back to turn 1 and 2. I think lap times would be around 2:30. I wasn't driving. I had an instructor who could push the car harder than I could (better driver) and I was holding the video recorder. He turned the engine as fast as possible. The entire straight it was up to 6600 in 3rd, shift up to 4th then 6600 shift, etc. You shift to 5th a bit before braking at the slight rt hand turn 1. The long turn 2 corner was at near 6000 probably in 3rd. I told him to rev as high as possible so I could get a good showing of what happens. Note that the foamy oil happens whether in a right or left turn, but the left turn is worse. Shortly thereafter, (next track session) I realized my rod bearings were shot but didn't destroy the motor.

16. Anyone want to borrow the holey cam cover for their own testing? All I need is shipping. Marc Thomas lent me the cover to cut up for testing. I think one of the lexan covers has come loose, but I think it is still there.

Guess that's about it. Back to the airplane factory.