GlenL

We're rat-holing a bit on the entrained air issue. The high pressure isn't sucking air into the oil. The foamy oil is being sucked in in the first place. When that slop is compressed the air goes into solution and then explodes into foam when the oil isn't compressed any longer.

Some guys have used an exhaust "PCV" system. I don't know it it pulls much of a vacuum, though. Just shoots the blow-by and mist into the exhaust pipes.

The video does clearly show that foamy oil is being sucked in. What to do about that is the real issue.

ptuomov

In the case of this video, the foamy oil hitting the window is most likely not coming thru the pressure system. It's most likely coming up the oil drains and then hitting the cam lobes, which toss it to the window. The reason why it's impossible to tell for sure whether the oil is coming from the pressure system or up the oil drains is that in either case it first makes it into the lifter bore / cam lobes and is then thrown into the window by the cam lobes.

One way to find out is to plug or baffle the head oil drain closest to the window and reshoot the video. If someone is willing to take on the project, I am sure Louie Ott will lend the modified cam cover. It would also be useful to get a matched data log of engine and car speeds and g-forces, with and without the closest drain plugged.

WallyP

One of the engine mods that I did to a flat-six engine with push-rod tubes below the cylinders was to install baffles in the crankcase to help keep the oil from being slung into the head in turns.

Would that help the 928 engine?

Mike Simard

I just did something like that on my engine. Machined bits that extend the drains to past the crank centerline. Only on the left side, the other side is already protected. The left side drains come out right at the crankshaft!

I did see problems with the left head getting full of oil. That's on a dry sump race engine and I only noticed it after long straights.

I don't think it has anything to do with whether the car is in a turn and more to do with the crankshaft spinning at high speed and blasting the poor oil drains. A long straight had more of that going on. My tracks also are CW.
That was also with a fabbed dry sump pan so a stock pan may be more troublesome in turns perhaps?
A Greg Brown pan spacer may help alot here.

Tony

I think you have to look at what the car was originally designed for. Highspeed cruising on the Autobahn. You want all the oil circulating and cooling that you can. Most Autobahns Ive seen don't have 1 g sweeping left handers!

The engine is well with in its design limits for what it was "intended" to do.

ptuomov

Not that I am an expert on this or anything, but it does make sense that the oil coming out of the wet sump in a left turn will make it to the crankshaft and get thrown up into the heads. In constrast, with a dry sump engine this can't by definition happen ("sump" is "dry," after all) and the left-hand corner may be irrelevant.

I think Louie's video of and commentary on a wet sump engine and your experience with a dry sump engine are evidence for the wet-sump 928's special problems in left corners being caused by the oil coming out of the deep part of the sump. This may already have been obvious to everyone, and I am just slow.

slate blue

I had never seen that video before so thanks Louie for going to all that effort! As I will have a high revving engines I need a very high quality supply of oil to the engine, so I thought, how to do that? Most makers will not share their info, it costs money and I need to implement a custom solution, one that cannot be purchased off the shelf and also if I had to pay for a top pro to make one up that would be the end of my budget.

The solution was to buy a used F1 oil tank, that way I can see how they do it and apply the technology and reuse what ever possible. They have some pretty exotic pipe work, how about a composite titanium carbon oil pipe! This is for use only with a dry sump of course.

Greg

Lizard928

Greg,

That is pretty slick! What is the capacity of that tank?

Brian,
21GPM was what Mark A stated from the manual when I asked that specific question when I was designing my dry sump system for my car (need to know how much oil can go in, to know how much to go out).
I went way overboard here. My drysump pump will move (at redline) nearly 90GPM of oil between the 3 stages. I wanted to be able to have each section of the pump be able to pull out more than the pump could put in so that in all situations I would never have a pool of oil in either end of the crank.
I also went with an air oil seperator off the back of the scavenging pump to help de-airate the oil prior to it being returned to the sump.
The tank will be mounted in the passenger footwell, like Mike Simard has done. However I will be having a thick poly screen at least for testing, and on the tank a sight glass the whole way down. If I see that sight glass fill with foam (as suppose to oil) then I will be backing off and coasting into the pit and further rectifying the system to prevent this.

The average drysump is supposed to have 150% of the original oiling systems volume. The air/oil separator is supposed to reduce the required oil volume by 50%. So technically one could get away with around 75% of the original volume.
I plan on making my own oil tank, and will probably make it large enough to hold 20L (more than 200% of stock) to help combat injestion of aerated oil.
With the pump I used I will be able to pull up to 20 in HG vacuum in the sump. I however will be limiting it to around 3-5 in HG vacuum to start. The vents which will limit that vacuum will be placed in the left side head (the one that gets the oil thrown into it), to help create a downdraft and prevent any oil from being thrown into the heads.

I do agree with Mike regarding the venturi effect of the #2/6 main. I have already opened up the channels and will be adding a piece into the oil channels to help push oil into that cavity.

IcemanG17

Colin
Thats right.....I can always remember the "stats" its much harder to remember who I got them from!!!

Bill Ball

Kevin Johnson's kit includes shrouds for the oil drains that should stop throwing to the heads from the crank.

AO

Nothing of value to add, but wanted to say this is interesting stuff. Carry on.

ptuomov

This is very interesting. When is your car going to be ready?

Where will your scavenge pickups be? I am just thinking out loud. This may be relevant for the following reason. The crankshaft is rotating counterclockwise (driver's perspective) and paddling oil towards the head. By paddling, I mean 3300g of centrifugal force at say 7000 rpm and 6cm counterweight throw.

I can't see any amount of pan vacuum beating that 3300g force, even absolute zero pressure. The oil is going to the heads if it hits the crankshaft on the right side (driver's perspective), and the vacuum pump doesn't get a veto on this.

The only two ways I see one can solve this are: (1) somehow prevent the oil from hitting the crank and (2) scavenge the right head with a pump. The first solution is preferred but may not be possible, so maybe it has to be augemented with (2)? I don't know.

The left turn is relevant here to the extent that there's oil in the crankcase for which gravity is relevant. At 1g left turn, the engine is laying effectively flat on it's right flank (driver's perspective). If the crankscase is either dry or all the oil is being hit at high velocity to some direction, gravity and the g-forces due to cornering are probably less relevant. But if there's free oil draining "down," it'll get hit out of the ball park by that crank. Left corner gives the easiest pitch, but the crank can probably hit harder pitches as well.

In summary, it seems to me that attempting to use crankcase vaccum to stop the oil from beeing thrown into the head is going to be about as effective as attempting to stop a bullet aimed at one's *** by farting at it. Do you guys agree?

Vilhuer

Factory could have easily made oil drains from both heads to go much deeper in the pan instead of dumping oil to crank. This is one of those simple mistakes which would have prevented a lot of headache if some engineer would have thought little further back in early seventies.

Louie928

Great thread with a lot of good info!
It's been several years, late '90's-early'00s I guess, since I did the oil check. I figured out a few things since then. One is that an Accusump really won't help with the 2/6 bearing problem, other than on a very occasional pressure drop. The reason being that once the oil gets aerated, and the Accusump dumps, the Accusump gets recharged with aerated oil. Next time it dumps it dumps aerated oil and doesn't help much if at all. Further, if it has been several minutes since the Accusump has been recharged with aerated oil, a lot the air could have come out of the oil and is in a big air bubble at the top of the Accusump. Next AS dump could put oil and a bubble of air right at the 2/6 bearings.

The sump cover shown on my web site isn't as effective as it should be. I feel it doesn't have a large enough drain back area and oil pools on top of it. I have seen a slight oil pressure drop, down to 3.5 - 4 bar, in the big left turn two at Spokane. I didn't see a pressure drop at turn two Thunderhill, but the Spokane track is worse. I'd advise to not attempt copying the sump cover on my web site without improving it. I figured a spacer to lower the sump would help increase the distance of the crank to the oil so I made one. I was the first one to try it so there wasn't any experience with that at the time. The spacer isn't a cure all, but logic would dictate that it helps especially with the longer stroke crank. I might add that I have 24k miles on the engine now and the spacer sealed with nothing but Yamabond 4 does not leak. Not even a dark spot of dust collecting on the seam. The material is 6060 T651 and was made from flat plate. It is ground flat, not rolled. I made the aluminum spacer to use the sump to add rigidity to the bottom end as much as for improved oil control. Stroker engines have cracked the block above the main bearings and I wanted to do something to help prevent that.

Back on the holy cam cover.... There are several holes in it so you can see oiling all along the the length of the head. I was at a PacNW drag session at SIR (Seattle, WA) and had the holy cam cover on. Several of the group observed the oil as I revved the engine to 6500 and held it for a while. No excess oil and it all ran easily down the drain back holes. That put a hole in the theory that the oil supplied to the head needs to be restricted. The problem only happens when you go into a turn at high speed. Either right or left turns are trouble, but the left hand turn is worse. It takes a while for the aerated oil to clear. As seen on the video, it barely begins to clear while on the nearly 1 mile long straight before the first turn and it turns to brown milkshake again. Wish I had more data collection, but at that time decent data collection equipment cost tens of thousands and I had nothing. Hmmm, there's been no change with that. I didn't even have audio and the little camera was borrowed from Heinrich with video fed to my 8mm video camera. I suppose lap times were around 2 min+, but have no clear idea.

I'm not sure about the 20 gal/minute oil flow. I'd say more like 8-9gpm max. The oil pump is not submerged so it has to "suck" oil through the pickup tube to the pump. Assuming the pump (at its inlet) can pull 30" hg vacuum all you have is atmospheric pressure to get the oil to the pump. The pickup tube is 23mm ID, but the oil has to take a rather convoluted path through the block to get to the pump. I don't think you can flow 20 gpm of oil through that path under a max of 14.7 psi pressure differential even though the lift is only a few inches. Just observation. I've not done any testing on it. The oil has to get to the pump first. Aerated oil will cavitate at turbulence points on the inlet. Evacuating the crankcase to below atmospheric pressure will make the oil even less likely to reach the pressure pump unless it's fed from another pump from an external tank such as with a dry sump system.

When I made the oil froth video, I believe my engine was already damaged from a failing 2/6 bearing. I believe I damaged the bearings at Thunderhill. I ruptured one of the stock crankcase breather hoses and blew out a lot of oil. I didn't know I had lost oil at the time, but did see the oil pressure drop to near zero in turn two. I came in and saw oil everywhere. I quit for the day. I was working on X pipe development at the time and did more than a hundred dyno runs plus a couple track sessions during the summer. I couldn't figure out why my baseline dyno power kept dropping when I'd try another X pipe test. I checked everything I could think of and replaced all the usual suspect components, but no help with the power. It was down 10hp, then 15 and finally almost 20hp down. It was during this time, (September) I did the oil video at Spokane. Next track session at PIR in November, the car was just sick and I noted the oil temp was hotter than it had been running. I quit driving it. The oil filter had metal. I think the damage wasn't extreme when we did the video and I doubt it changed the results. The oil temps were still ok at that time although dyno power was down. The "burst" breather line coupled with the oil video really got me thinking about crankcase pressure, and oil aeration. Redline 20W 50 oil during that summer.

The holy cam cover is available for anyone to borrow and try another test with data collection this time. It would be interesting to see the effects of a good crankcase baffle/sump cover installation. Some of the lexan seal has come loose. It's glued on with orange RTV gasket material.

Bill Ball

Louis: Sorry if you have posted this already, but did you change the behavior shown in this film with the breather mods you discuss and/or the spacer? Did you try shrouding the drains or do you think this is mostly breather gas flow-related?