The current configuration is of the keep-it-simple-stupid variety. Four breather ports in the valve covers and one very large one in the oil filler neck. The valve cover breather ports have shroud tubes inside and the elbow fittings have been drilled open. Five ways out for the crankcase gas.

Two valve cover ports, one on each side, are directly connected to a pitot tube in the intake upstream of the turbo. The theory was that at low rpms the system will feed fresh air to the valve covers and at high rpms it'll breathe out thru the same hoses. Who knows what it actually does.

The two other breather ports and the large oil filler neck fitting go to a ProVent 200 inlet and then there's an oil drain from there to the pan and gas exit that can be fed directly to the atmosphere (current arrangement) or to a slash-cut tube upstream of the turbo (already in place, just not used currently). The MAF elbow breather connection is blocked off, and the hose from the oil filler neck to the intake manifold has a check valve in it.

We'll have a more ambitious system in the next version. The ProVent will drain to turbo oil sumps and will be actively scavenged from there to the pan, along with a couple of other changes.

 

The size of the lines make a big difference. If the lines are to small velocity stays high and the oil can not fall out of suspension. Spark advance played in to my original issue. Advanced the spark at higher rpm ( on the dyno), cut the oil being flung around a lot.

 

Tuomo,

Do you retain a baffle in the base of the filler neck or leave it open?

Regards

Fred

 

Andrew,

Did you retain a baffle in the base of the filler neck? I use a 1 inch vent connection to the pro vent but no other connection at the moment.

I am concerned that my problem may be more ring wear related but would like to ensure I have not done anything stupid to exacerbate the issue.

Regards

Fred

 

I have John's baffle box there, but without any scrubber in it. Just the box. The box design is IMO very good, with a lot of flow area that slows down the gas. But the scrubber doesn't help in my design, so I don't have that.

Here's the design, mine is like that minus any of the scrubber inside:



For my purposes, I need this to flow a lot of gas at all times when it needs to flow gas. For my setup, a some oil getting thru here is less of a problem than the box not flowing enough gas.

 

Porsche designed for later 944 and 968 2,7L and 3.0L engines similar "windage port" system we have seen in GTS. The purpose of this was also to balance the pressures between cylinder sections.

There is also their own conclusions about the idea of the design. Scroll down, story starts after middle of the page.

http://www.lindseyracing.com/hptalk/0808.htm

One of the most recent additions to our Machine Work and Engine Services we can perform on your 2.5L engine is what we call our "Windage Port". This can be described as a port or opening at the base of the cylinders.
One opening is between the base of cylinders number 1 and 2, and the other is between cylinders 3 and 4.

 

Fred - 2 things:

1) I'd remove the small connection to the filler neck - it could still be ingesting lots of oil there, though in that case it would be surprising if the Provent filter element wasn't seeing plenty of oil too.

2) Are you sure the check valve to the rear cam cover port is still good?

The stock system flushed in though this port some of the time - but didn't have a check valve (flow reversal was possible & certainly happened). While fresh air flushing is probably a good thing - I think you could plug those temporarily for a test period without any harm - many have done this, my car has this connection removed/plugged.

I agree that its challenging to avoid crank pressurization when evacuating the crank via a provent or other AOS without using a vacuum source.

Using the intake & pre-throttle body venturi vacuum as a source also has its challenges - you don't always really have what you need - e.g high RPM overun.

A vacuum pump provides a more predictable source assuming you have a well sealed crankcase & heads. It still has other challenges of course but at least you have have good vacuum at high rpm under power or on overun.

Alan

 

My Lindey Racing "built for reliability" 2.8L stroker lasted 4500 miles before it started self destructing. I would not use them as a source for reliability solutions.

 

Here is my understanding…

To reduce oil usage the idea is to eliminate positive pressure in the crankcase.

The problem with using intake vacuum to reduce the positive pressure is that oil gets sucked in and burned AND the intake vacuum is not reliable enough source of vacuum in some situations.

The problem with using a vacuum pump is having enough vacuum to eliminate the positive pressure without pulling so much vacuum that the crankcase seals are compromised. Large enough piping to eliminate the positive pressure created by blow by and/or piston movement would pull too much vacuum on the crankcase in situations where there is not that much positive crankcase pressure being generated.

Since I work for a company that make oil & gas controls for oil & gas production the solution seems obvious to me.

Instead of trying to rely on piping size or venturi to set the maximum vacuum an external pump would pull, put a vacuum regulator between the crankcase and the vacuum pump. This would allow big enough piping to be able to handle the maximum positive pressure and or pulses in the crankcase without pulling too much vacuum and compromising seals and/or power. Of course you would need another regulator between the inlet and outlet of the pump so the only pressure created on the outlet of the pump is the extra crankcase pressure. Which once scrubbed of oil could be introduced back to intake vacuum or vented to atmosphere if you were not concerned about emissions.

The best place to scrub the oil from the vent system is between the crankcase and the vacuum regulator so the oil can drain back to the crankcase at crankcase pressure.

 

If one can install a vacuum pump that actually pulls a meaningful vacuum in the crankcase, then a regulator is a good solution. The regulator should however not be in the line between the vacuum pump and the crankcase, but instead in the line that supplies the clean replacement air to the valve covers. This way, the vacuum pump will always do something useful, namely ventilating the crankcase.

 

Sizing and speed of the pump is actually not too difficult.

You can run up to 15" Hg of vacuum in the crankcase with no problems.
More than 15" Hg requires a forced oil feeding to the wrist pins. A high vacuum will never cause problems with the seals, especially in our engines.

You can add a vacuum limiting valve as Alan has done to the cam covers which prevents the system from going over 12-15" Hg. But with the pump and pulley properly sized, this never is a problem.
Jake has seen a high of 12" Hg, I see around 9" Hg on the GTS I did, and mine sees around 10" Hg with boost. At these levels there is no need for a limiting valve, or anything else. The pump is turned by a belt on the crankcase so as you rev higher, the vacuum pump does more. At idle 2-3" Hg is normal. So long as you are between 4 to 15" Hg vacuum at WOT your windage problems are eliminated.

 

Then sign me up! My GTS uses a quart of oil every tank of gas.

 

This was also my thinking.

I have adjustable vacuum limiting valves feeding to the rear ports on both heads - dual purpose on these:

1) Failsafe max crankcase vacuum limiter (its actually 2 VLV's). This hasn't been needed so far as I can see.

2) Fresh air flushing into the heads and down the head drain ports (but only when the blowby volume isn't too high).

This second goal requires the VLV's be set to a threshold level where at med rpm with low blowby flows the valves can open to flush the heads/crank with fresh air - but that they close under high blowby volume cases - e.g. esp. high rpm low load cases.

Still working on this set-up. To some degree high blowby limits vacuum all on its own - but a more active solution based on rpm and intake vacuum (load) may also be needed.

First I'd like to chart actual blowby volumes by engine conditions - but this has some complications... I do have an airflow meter and have built some adapters for its use (exhaust and AOS vent line) but I don't have any good measurements yet - only theoretical models.

Alan

 

Roger will be having them ready very soon.

 

1. I have tried blocking the small connection- did not seem to make any difference. I think the JK scrubber is so effective it knocks all the oil well and truly out- the interesting bit I'd like to know is just how much differential pressure it creates- and how much is too much?

2. There is a write up on Louie's website about the stock breather system and how it works- seems to make sense to me. The pipe from the rear passenger side cover is -according to that analysis- bi-directional. The theory suggests it in-breathes at low rpm's and out breathes at higher rpms and that might help explain why higher speeds increase oil consumption [when I had the stock S4 system]. Trying to replicate the GTS system was clearly a mistake seemingly going from something that was less than perfect to something possibly much worse.

My current efforts have been to try and attenuate the problem as I try to determine whether I have a ring problem or something that can be improved by major surgery.

I have liked the idea of Colin's system since I first learnt of it- sounds as though you gain a little power to pay for the parsitic losses of driving the vac pump- which are not much anyway but if it gives a lot cleaner burn that has to be the best solution.

I have kicked myself a number of times for not putting in new rings when we had the motor out and partially stripped a few years ago when I transplanted my S4 motor into this chassis. We saw no signs of need at the time and more to the point, did not want to disturb the bottom end unless I really had to.

Regards

Fred.