FredR

Having read this thread and others on Greg's offerings and trying to link this to what I have seen and experienced as I try to sort out my S4 motor I have come to a number of observations/conclusions:
1. Everyone knows that 2/6 failure is almost a given on these motors when tracked.
2. Whilst sharktuning I have wondered why advance at high rpm's/load is controlled predominently by cylinder 6 then cylinder 2 with little or no retard being applied on other cylinders.
3. My oil consumption has always been diissappointing despite not being able to find anything obvious as to why that should be.
4. There seems to be an rpm threshold -probably about 4k rpm when oil consumption in my S4 motor rapidly increases and gets proressively worse the harder the motor is worked. It seems I can lose a litre of oil burning a tank of fuel.
5. I cannot see signs of oil burning on the plugs- not that I can tell at least but the plugs look very clean.
6. I initially assumed that 6/2 initiated knock because of superior air flow but perhaps that is completely wrong. Maybe it is because the oil blow by is simply much worse on these cylinders.
7. Our knock control system is very good and perhaps hides problems other motors would have had many problems with.
8. Having sorted out my fuelling I then started trying to work the ignition timing. In the low to mid range I was able to get some good gains on stock but on the top end it was a different story. Our fuel [allegedly 95 octane] is a bit suspect. However, instead of running around the stock advance of 30 degrees at full load rpms I had to pull timing back to about 24 degrees. The knock problems seem to start at about 5500 rpm. My motor runs very strongly up to that point. Thereafter it feels a bit non descript.
9. I initially concluded that something was amiss with my motor- and maybe it is but this thread and others suggest tha tmight not be the case.
10. Looking at the sharktuner EZ plot it seems there is a noticeable line of knock events starting at 5500 rpm.
11. During my logging runs and running high revs I noticed the low oil level alarm light popped on a few times but when checking the oil level at rest it was fine. This suggests oil packing the heads.
12. I know there are well tested theories about 2/6 failure but all this makes me wonder whether idetonation is wiping the big ends on this journal if they are relatively soft as Greg advises. If the oil pickup is being exposed does it make sense that only 2/6 should have a problem with aerated oil? Maybe it is relatively less well lubricated than the others.
13. When my motor was in the late S4 I was never happy with oil consumption but when I purchased the GTS [with TBF wrecked motor] I converted my S4 breather system to that of the GTS since I had the parts- but perhaps that was a mistake and I have unwittingly compounded the problem.

At least I feel there is a bit of light at the end of the tunnel if I can reduce the oil that is being lifted.

Now the real question in all this- is there any logical reason why cylinders 6/2 should lift more oil than the others?

During recent sharktuning I isolated the inlet from the recycled streams and it still pinged so it seems the oil is getting into cylinders 6/2 preferentially.

I now want to improve the oil lifting problem but this problem with preferential pinging on 6/2 is what bugs me. Maybe this can be stopped.

Regards

Fred

Mike Simard

That's very interesting and calls for some random guesses!

The only way I know to link 2/6 oiling with detonation is if the 2/6 rod journals saw reduced oil over time the rings didn't get enough splash lubrication, wore and allowed a little more oil into the cylinder which lowers the effective "octane".

GregBBRD

I think if you read back on this thread and you read about my goals with the "street ventilation kit" you will see that my ventilation kit is complex and involves multiple changes....for multiple reasons. If all I wanted to do was remove oil from the intake, that would have been very simple. However, since of of my goals was to be able to return the oil to the crankcase much quicker, there are changes to make that happen, also.

AO

And that may, indeed, be the root cause (or not). Of course we don't know for sure. But the car/person you allude to has significant power and does not, so far, seem to suffer from any oiling issues in a 100% completely bone stock motor (i.e. stock heads, rods, pistons, cams, crank, oil pan, etc.)

Could it be that the oil scavenge system that has been developed for street use is to make up for deficiencies in other areas? Could it be masking problems with knock, crankcase ventilation or some other contributing variable? I think it's at least plausible. Don't get me wrong... I'm not suggesting that it was developed with these deficiencies in mind, but rather as a result to alleviate the symptoms.

I think what Tuomo is trying to get at (and at least I am too), which is the symptom and which is the cause?

So let's say for the sake of argument that crankcase pressure is the primary cause for oil packing in the heads. We know detonation and pre-ignition are one of the the primary causes for crankcase pressure buildup in our engines. If so, with insufficient/inappropriate crankcase ventilation at high RPM or a g-loaded event or both, you've got a recipe for a disaster. We all know that the stock crankcase breather setup recirculates vented gases back through the intake. This "oil soaked air" leads to more detonation by reducing octane.

The stock knock control system (if you have an 87 or newer) will attempt to correct this, but at a max retard of 9 degrees, I'm not sure it's enough to cope with the lowered octane of the "oil soaked air." If it is not capable, then the cycle exacerbates and gets worse until the driver lifts off the accelerator or the engine goes boom!

There are a lot of "ifs" in that logic train, so it could easily derail. But it seems to make sense to me for now.

Now, I forget who posed the question (Tony?) but but someone asked what George Sunen does for his ORR car? He has by far the most seat time in a car at those high RPMs than anyone I know of. I know he and Bill Ball have spent significant time SharkTuning to make that thing run as good as it can. But given the extended duration at high RPMs coupled with the boost, I would be surprised if they allowed for any knock. Maybe even built in a little safety margin (but that's speculation).

I think it's a little different when you whick up a motor to see what kind of power it can spit out and you see 20-30 knock counts vs. sustained driving at high RPMs. Anyway, my point is there is evidence to support that a properly tuned (and possibly vented) 928 engine does not have to suffer from oil packing in the heads.

But this all hinges on what is the symptom and what is the cause.

Just more fodder to consider.

john gill

I am amused that the 2/6 bearings get mentioned often!
In my particular case (3 engines) it has always been the front 2, 1 and 5, these are the first to see low oil pressure and suffer damage from lack of oil , actually the rear 2, 4 and 8 in 2 cases were not damaged at all , and it was obvious from the graduated damage from front to rear that lack of oil was the culprit .
I will be tracking the car with the additional oil pump this year.
I also tried to go the electric route, but could not get the volume required and the efficiency of the belt driven 2 stage pump. Until speaking with GB who came up with his working solution . Interesting that the early 16v cars dont have this problem until you ventilate the cam box , I tracked an early car with slicks on it in the club sprints , and the bearings were unmarked.

Cheburator

Your meat is my poison, John...

My race engine was destroyed thru lack of oil in the tank. When we opened her up - 8 galled bores, 8 galled pistons, 2 bent conrods and 2 bearings gone. And I mean gone, turned into powder. Can you guess which cylinders were these? The other 6 mains were perfect - as any bearing which had only done 5k miles on a dry sumped engine should be...

So far three early cars in the UK have had multiple engine failures while racing... Always 2-6...

Rob Edwards

Holy crap, I've solved it! It's the Coriolis effect!

andy-gts

by Jove I think that boy is onto something!! haahhahaha

GregBBRD

Fred:

My guess wouild be that everything is normal with your engine and it is pushing oil into the intake. Unless you pull the spark plugs immediately following a high speed run, seeing evidence of this is difficult. The easiest way to tell, is to go out, get it warm, run it at high rpms, shut it off, and immediately pull the MAF and open the throttle. That lower plenum will probably be a "lake" of oil.

Yes, the addition of the GTS filler neck and "updated" hose from the filler neck to the intake "added" to the problem....actually, depending on what you did with the passenger valve cover (see below)...you might have made the problem worse than a GTS engine (difficult to believe that could be possible, but it is.) The "updated" filler neck and hose reduced the amount that the crankcase could ventilate. The "opening" of the driver's valve cover to the passenger valve cover added a "vent" at the top of the valve cover, so that, in theory, the oil in the head could return easier. (S-4 engines had this valve cover plugged....making oil returning to the crankcase even more difficult....once the "drains" filled up.)

Chances are, if you directly installed the S-4 engine, you have an "unrestricted" elbow on the rear passenger side of the engine. The "late" GTS engines restricted this opening, to reduce the amount of oil that could be pumped at a given moment, into the intake.

Once you get "rid" of the oil in the intake and "knock" off the thick deposits (from the oil) out of the combustion chambers, you will be able to add timing....and your "knock" issues will not be so problematic in cylinders #2 and #6...which "catch" the brunt of the oil from the intake.

You'd be really happy with my VK-1 Kit. I personally guarantee that this would be the best money you could ever spend on this stock engine. It cures a whole "list" of problems....much like the items you "listed" above. This kit addresses and fixes what Porsche never could fix with the 928 engines.

Alan

Actually Greg I have little idea of what your "Street Ventilation Kit" is or how it differs from the scavenging "full on" kit in goals or implementation... I did read back through this thread as you suggested and I don't really see anything? maybe its somewhere else in a different thread? Maybe you can point me to it..

I don't expect you to reveal all... but certainly seems the street kit doesn't include the active head scavenging? Not sure what the goal differences are either - I'd assume only street use on ~stock engines?

Be nice to have a general idea of what areas you changed in each.. At the level of say: Changed breather system routing, added provent, modified head breather ports, modified oil pan, added windage screen, etc

Just scope of what systems get modifed - not so much exactly what or how... it would help to comprehend the differences & scope.

So - still lost on the differences between these two systems. You obviously know exactly what you have done - but are reluctant to say too much - I feel like as a result I and others have little idea (or maybe I'm just being dense). Most of what I think I know is just deduced from the pictures you showed, and a few snippets revealed.

I really do understand about protecting against competitors - but potential customers need to know enough to at least decide between these for their own potential use - no?

Alan

Tony

In a "street" application and the driving that 99 percent of us do, when is getting the oil back to the crankcase EVER an issue?

ORR and track i can see, for the daily driver, never.

So the oil return for a typical 928 daily driver in street use is inadequate?

Speedtoys

Depends what the daily drive is...doesnt it?

But still a valid point.

Tony

Without the "google" how many times do you see this in your daily drive.

In about 14secs most of us will be doing jail time.

Hilton

Alan - the link to the thread about Greg Brown's passive system was posted by Rob Edwards earlier in this thread: https://rennlist.com/forums/928-foru...ation-kit.html

But this thread is digressing somewhat.

The problem of 2/6 flow is being lost among the problem of "how to remove oil from the heads". I realise some will say "well scavenging the heads is the solution to 2/6 failure" - however, removing oil from the heads is treating the symptom IMO.

The problem as I see it (and I'm neither an engineer nor a mechanic) is that the pickup is getting uncovered and entrained air is killing the 2/6 bearings first, per the awesome link in the OP. So - the real question in my mind is, how to keep the oil in the pan? (and not - "how do we put the oil back into the pan from places it shouldn't be").

I think Tuomo's idea of monitoring pressures is an excellent one - if someone has a setup that can do such, it would provide excellent information. I'd love to see readings at each possible cam cover breather position, compared to pressure readings from a sensor in the dipstick hole (as that's close to the pickup - which is where we'd like low pressure, to both encourage flow back to there, and to encourage bubbles to come out of solution). Call me greedy, but I'd even like to see those readings twice, with both a stock S4 and a stock GTS breather system.

Mike Simard's comment about modifying the drains on one side is also a great start to preventing oil-throw plugging the drains.

Alan

Thanks Hilton - guess I missed that - lots more details there. Read it a while back (and responded) but mostly forgot the whole thing... getting old I guess.

Agree with your other points.

Re-reading this -

My system concept is likely very similar to Greg's but different in some respects - I believe rather strongly that all breathing should come out of the huge main crankcase vent with no breathing at all out of the cam covers. I do have all 4 cam vents added & opened up - but they do only head to head balance + in-only flow for flushing - so all static flow is always down the head drain ports, fully aligned with the oil flow-back direction, there may be momentary reversals for pressure equalization but none sustained - I believe this is actually a quite important difference...

My Provent is also evacuated into the existing PCV ports, I suspect rather similarly to Greg's based on the hardware I can see - it seems I have rather more check valves in place though. I do also want to add a blow-off option into the air pump in case the total PCV breathing capability ever isn't enough - but that isn't plumbed in yet. Of course in the interim the provent has its own built-in blow-off and vacuum limiters. The Provent sees plenty of oil - seems its always freshly wetted - but the output side is totally clean of all oil deposits - so seems it works very well.

Alan