The difficult of install I would call easier than the other systems on the market today.
Greg's kit requires both cam covers and intake to be removed.

As to routing it back into the intake, entirely possible, especially once I have my AOS completed.
Install can be done in a few hours.

The problems with all of the other ways of venting the crankcase is that you don't get rid of the pressure surges below the pistons which can cause ring flutter.......

 

This works..we inspect for in in Spec944 racing. its a bitch to inspect for...but people do it and it pays.

 

I thought ring flutter was more a function of ring mass than crankcase pressure surges. And I thought crankcase surges are more worrisome for detonation (oil getting past rings and into the combustion chamber).

 

The inline four has a windage pattern that is relatively easy to cure precisely with those breathing windows between cylinders 1&2 and cylinders 3&4. For cross-plane V8's, the problem is different. The most urgent need would be somehow connecting bay 1 with bay 4 to relieve the most extreme pressure differences.

Ring flutter depends on many things. One is the pressure differential between the cylinder and the crankcase. Lowering the crankcase pressure or increasing the cylinder pressure reduces ring flutter. For conventional shape rings, for a given ring material, the ring width is what matters (because the mass and area cancel out). Finally, too much oil on the bores will unseat the ring from the wall a little bit and let pressure between the wall and the ring, undoing the gas pressure mechanism that keeps the ring sealing to the wall.

 

When you have oil getting in the intake, does that lubricate the (Alusil) cylinder walls better? Has anyone opened an engine with a breather system that completely eliminates oil in the intake? How did the cylinder walls look? Was there any wear steps on top and bottom of the bore where the piston ring stops?
I understand the problem with oil consumption in our engines, but why would Porsche with all that racing experience design an engine with such a problem for years? Where they inexperienced? Or did they just not really care and were too busy improving the 911 for the future. Or was this a common problem for most manufactures back in the day and they didn't know how to tackle the problem?

Ali

 

This certainly isn't the right way to lubricate the rings... it might be a good way to break them though - via octane reduction & knocking.

I think they made some bad choices - latterly almost certainly under pressure to spend the minumum needed while the replacement models were being readied.

Alan

 

I always imagined an engineer saying, "Why don't we just put this on the gas cap and be done with it?" Employee of the month.

 

For those that may be interested, the key to liquid/gas separation is "Coalesence". The mist criculating around in the crankcase has very fine particules of oil dispersed in the gas phase. To separate these you need to facilitate a mechanism to allow the particles to come together [coalesce] so that they are physically big enough to overcome entrainment in the gas stream. Thus a system design controls the gas velocity reducing it to a point where the particles that are formed can drop out freely.

This is precisely what JK has done with his baffle design creating a larger flow area into the baffle and then installing mesh to form a large surface area upon which the oil droplets can attach to and thus coalesce. The larger particles can then drop out under gravity falling counter current to the gas stream. Where JK's design has been challenged is whether the pressure drop across this baffle plate is too high. On my current system all the gas vented goes through this channel, it seems to take out the oil leaving nothing for the Pro Vent to do. However, oil consumption does not seem to have dropped so my next step will be to see if I can also vent via the cam covers into the Pro Vent.

The Pro Vent itself is also another clever piece of kit. The tangential inlet does two things- it induces the gas stream to flow circumferentially in a larger cross sectional area bounded by the height of the chamber and the width from the outer wall to the inner screen thus slowing down the velocity. By moving the gas stream in the chamber [initially] circumferentially, this causes some of the [heavier] oil particles to move towards the outer wall where they can coalesce and drop out. Then, as the gas stream has slowed down it then tries to leave the outer chamber via the inner fine screen that also knocks out oil particles. The gas entering the inner chamber does so across a large area bounded by the inner circumference of the screen and its height thus slowing down the gas ever more further optimising the potential for particulate matter drop out before leaving via the gas exit port.

In my case I am seeing nothing taken out of the Pro Vent so my conclusion is that either the JK baffle is too restictive to act as a sole flow path or [more likely] I have a deeper routed problem with excessive blow by due to wear or other problems causing too much oil to pass the pistons. I hope not but...?

My next step may be to try what Tuomo has done and remove the wire mesh from the baffle and perhaps [initially] try adding the vents from the cam covers directly to the Pro Vent inlet. I was against this because it induces gas to want to flow up the cam tower drain chimneys which [I would think] is the last thing we really need given the tendency to pack oil in the cam tower at higher rpms.

When Porsche designed the original 928 motor they probably did a very good job. When they went to the 5 litre variant it probably did the motor no favours and the GTS- well in stock form maybe they just did not do their homework properly- but- given the mods to the drain passages [or whatever they are on the GTS crank case] and the various mods to the GTS breather system, they must have known they had issues- just a case of how well they did or did not solve them.

At least Colin's system appears to offer an alternative course of action. That GB can build his wonderful reliable stroker motors without oil consumption issues also says something.

Regards

Fred

 

Porsche does not consider oil consumption too much until it is more than a quart every 500 miles.

My GTS was using about this until the cam crash rebuild.
Didn't matter what oil I used.
If I put in some Restore or Lucas Oil Stabilizer it would use much less oil.
Sometimes, on long highway trips it wouldn't use any oil at all and was random, sometimes with the restore/stabilizer, sometimes not.
Seemed like the oil would just suddenly drop a quart.

After the rebuild it is using a quart 1 quart per gas tank, or about ever 300 miles consistently.
The intake has very little oil in it.
It does not visibly smoke but there is a lot of oil soot in the exhaust.
The condensate that comes out of the exhaust pipes when cold is black with oil soot. Leaves splatters on ground.
Sometimes, before the engine warms up I can smell raw oil. No visible leaks or spots under car.

I wonder if I should have drill the oil scraper ring relief holes while it was apart.
It was cleaned well, all the carbon off the piston tops, etc. Checked the crank and rod bearings but did not pull the pistons.
Just passed 70K miles.

Haven't tried the Restore or Lucas Oil Stabilizer since the rebuild.

 

+1

 

[QUOTE=RKD in OKC;1096
......it is using a quart 1 quart per gas tank, or about ever 300 miles consistently.
The intake has very little oil in it.
It does not visibly smoke but there is a lot of oil soot in the exhaust.
The condensate that comes out of the exhaust pipes when cold is black with oil soot. Leaves splatters on ground.

[/QUOTE]

Exactly what I see/experience with my S4 motor

Rgds

Fred

 

I have run my S4 extensively with no oil returning to the intake and have seen absolutely zero wear on the inside. 257k miles and no real noticeable wear at all.


AO,
Tuomo summed that up nicely.

RKD,
Simply put, the oil drain back holes are a wise idea, but I do not feel that they will have a very large effect on the oil consumed due to the full extent of the reason it is happening.

 

Found this nice article on piston ring tension.

Venting through the heads in a 16v is a no go as far as I can see unless you introduce a rather powerful vacuum pump like the one proposed in the opening post. I think long-term viability is still open for debate, but it looks promising.

On the 32v heads, venting through the heads is plausible, but I think some additional baffling is needed. But at some point in the upper RPM ranges, as Greg Brown observed, the heads may fill with oil and eject out these vents. That would be bad.

Personally, I think the vents on the 32V heads are unnecessary if you can vent sufficiently through the oil fill port. This is probably not an option for those running a stock oil fill neck as the ports are barely big enough for a flea to crawl through let alone any meaningful oil vapor. I think this is where the factory got things wrong on the 32v motors.

I also run a similar JK baffle but without a scrubber. The purpose is mostly to shield the main vent and prevent oil sling from the crank from plugging it up. As Fred mentions this should have nominal pressure drop because of its open design - and the Provent is allowed to do its job.

I will also be doing a complete refresh on my motor including valve seals, guides (if needed), rings, etc. So it will be difficult to get a complete assessment on the effectiveness of any breather redesign I employ.

 

Porsche screwed up with the 928 engine. Cayenne V8 a lot of the problems fixed.

If you are into fabricating complex stuff and have the engine in pieces, please try the following: Add big hoses from bays 1 and 4 to both valve covers. Try if it works and report back. I think that may work because the corner head oil drains will then just flow oil down. Furthermore, there will be an additional flow path for the extreme pressure differential between bays 1 and 4 to equate. Just an idea.

Here's a thread on my theories about what's going on in the 928 crankcase:
https://rennlist.com/forums/928-foru...ing-right.html

 

Tuomo,

What do you mean by bays? I presume you refer the chambers in the crankcase under cylinders 1 & 4?

Regards

Fred