Carl Fausett

Don - thank you for your excellent write-up. I have seen pictures of that approach somewhere.... each of 4 hoses from the valve towers up to top of the plenum, where they meet one hose that goes to catch can.

Perhaps if turning left and right side cam tower vents are "plugged" with oil momentarilly, the left side vents are breathing... and if turning right and the left side vents are plugged with oil temporarilly, then the right side is breathing....

Tom Cloutier

Hi Glen,

I knew I forgot something! I spent many hours in Solidworks drawing several different designs and built foam core mock ups on a flange salvaged from an old crashed pan. Everything looks good so far.

Regards,

Tom Cloutier

Carl Fausett

This engine is slightly over-bored for Chevy-sized forged pistons (cheaper) and lined with cast-iron cylinder liners... so cross-hatching is quit visible and normal.

GlenL

So the tip stays immersed. That way the blow-by prefers the block-top exit into the filler/separator.

John Veninger

Carl,

You can do a day of track driving with non-detergent to get the rings to seat, but are you sure it's a ring problem? There has been conflicting info on the value of total seal rings. May want to read a bit more.


I use to pump lots of oil into my catch can until I changed the configuration. I made a custom oil fill with two -8 vent lines, no tube to the pan. These lines went to an home built oil separator (like the one Tony made a few years back). It had a small -4 drain line back to the pan. Then two -8 lines to a catch can.

I was pumping almost a qt. into the can with a 20 min. track outing (nothing when it was a street car). The new setup showed about 4oz in the catch can. Saved me lots of oil!!

John Veninger

FYI- DON'T vent a 16V motor from the cam towers.

GlenL

I was contemplating this from below the car over the weekend. The line to the slave runs just below the pan and goes to the top-rear of the slave.. The slave could be mounted upside-down but that'd leave the line at risk.

BC

I think Louie likes the idea of drawing air DOWN through the heads (following the oil draining down) into the crank case and then back out thorugh the normal breather areas (which can be very large if needed - maybe even drawing some vac.

Should we abandon vac as a device for keeping the pressure low in the crank case?

GlenL

I put together this data using a simulation of vehicle acceleration. The base data is my 1980 Euro S drivetrain with the latest dyno charts. The graphs show what is happening in the oil sump as the car accelerates from 40mph in 2rd gear to 150mph in 5th. The acceleration is all at wide-open throttle. The "blips" are the gear changes.

The simulation uses the torque output, gear ratios, final drive and tire rolling radius to determine the acceleration, velocity, distance. (Those charts aren't posted) I've modified it to compute the angle that the fluid in the pan shifts to due to the acceleration. The shape of the pan is idealized as 12x12.75x3.5 inches (wxlxd). There is no analysis of the dynamics of the fluid's motion.

This graph shows the fluid angle of repose for the vehicle's acceleration at each point in time:



With the fluid at that angle, the effective volume of the unmodified sump and ejected volume was found. That's shown in the next graph. The ejected oil will be rolling out of the sump and onto the shallow pan deck.

The angle of the deck is about 5 degrees so when the angle of repose is higher than that the oil is running to the back of the pan and potentially into the rotating assembly. I was going to compute how much oil is force into the ratating parts but didn't make those measurements and the shape of the pan is complex. I'll guess that more than 1/2 quart and the rod nuts are hitting fluid.

An assumption is that there are 7qts of fluid in the pan. Could be less or if foamy then more. The fill level doesn't change the capacity. The graph explains why many racers and tracksters fill the oil 1/2 qt or more low after finding the first 1/2 qt or so almost immediately ejected.



This last graph shows the pan capacity and ejected volume after the addition of a sump cover. The cover that Kevin from I-J has fabbed extends out about 1.75" over the pan. This retains a good amount of oil compared to no cover. It could go a bit further but that can cause draining problems itself.



I'll be running the cover and new drains at Heartland Park in Kansas this Saturday. I am expecting a big improvement in oil control.

If any of you are around Topeka, drop by! I'll be the brown 928 with Minnesota plates...if there are any other brown 928s, or 928s at all, there.

If you'd like a copy of the Excel spreadsheet that was used for this, drop me a PM.

SwayBar

I am referring to the 'big ball of oil' that is always circulating around the reciprocating parts while the engine is running. Some refer to it as a ball of oil-taffy since it looks similar to when taffy as it clings to it's machinery during manufacturing . Here is a link to what I'm referring to, and it's 928-centric at that:

http://www.nichols.nu/tip682.htm

This is the key quote from the link made by Marc Thomas:

"The crank also spins up a batch of oil and keeps it in suspension, especially at high rpm. This oil cloud circles the crank and is the reason most race engine have "scrapers" in the case. Up to two quarts of oil can be circling the crank at high rpm! In some cases it can be more as the S4 is known to "pump" oil up the oil filler tower and keep it there!"

So back to what I was saying earlier. Bone-stock, the 928 engine by design is known to have this ball of oil in suspension, clinging on and around the crank/rods while the engine is running (..NOT circulating thru the oiling system), thus it is not in the pan. While in that state, the Porsche engineers knew there is 'X' amount of oil circulating through the oiling system, and 'Y' amount of oil caught up in suspension around the crank, leaving amount 'Z' in the pan. Knowing that, they decided upon a level of oil within the pan while it ran at various RPMs.

Given that state, what do you suppose happens when you take that 2+ quarts that are in suspension and scrape it off down into the pan with no other changes to accomodate this new state? The pan now has a 'running overfill' of an additional 2+ quarts, something which the engine was not originally designed for. Those 2+ quarts are now in the bottom of the pan where that pan was originally designed to be running with those 2+ quarts in suspension.

For any given corner, bump, acceleration, deceleration, there is an addtional 2+ quarts sloshing around in the pan, getting whacked and whipped up by the crankshaft over and over. Sure there is a windage tray, but who knows whether it is submerged by the 'running overflow' of oil introduced by the scraper? If it is submerged, the crank will continue to rotate and smack into the pool of oil.

Noteworthy, there is an additional 2+ quarts of oil in the pan for the sump to supply oil to the engine's oil system.

Jean-Louis/Agnes (..JLA), and myself just got back from 3 days of hard driving at Road America during Chicago PCA's DE.

JLA's 4.7L Euro internally has a GTS-baffle, and a newly added MURF928 Centrifugal Supercharger running 5 psi putting out 354 rwhp. The addition of the supercharger was solely to keep the GT3's from pulling on him on the straights since he always got them in the corners, but they pulled him on the front and back straight; mission accomplished as the Euro now slightly pulls the GT3's on the straights. The car ran 24 30-minute sessions, and total oil consumption was approximately 4 quarts, which is identical to it's non-supercharged consumption.

My GT engine has no baffles, and has the stock crankcase ventilation system, and I burned less than 3 quarts during my 12 30-minute sessions, which is better than normal as some report 1-quart loss per session. Granted, 2:45 isn't exactly scorching, but it is a decent time for the second time out in a 928 at RA (..2:31.61 is my best in a stock 02 Z06).

On the other hand, Sterling on the street reported double the oil loss after the installation of the scraper. Glen reported excessive oil loss after the installation of the scraper. The 12-Hour racer reported excessive oil loss after the installation of the scraper.

The addition of a scraper in it's present form dumping an additional 2 quarts of oil into the pan is upsetting the level of oil in the pan/sump when compared to the stock configurations of JLA's, Kibort's, and my engine, judging by our lack-of oil loss versus the scraper engines.

Aggravating that additional oil-level of the scraper engines is every bump in the track, every corner, as well as acceleration and braking forces; oil is sloshing everywhere, exacerbated by the extra 2 quarts over stock which was scraped off the crank.

However, those scraper engines do have an additional 2 quarts in their sump to supply it's engine, but unfortunately at this point, it is getting beat up like a bowl of egg-whites.

GlenL

Sways,

What doesn't make sense in your analysis is that the oil from the sump being whipped up is somehow worse than oil already entrained in the air and being whipped up. Stripping the oil out has got to be better than just having a "big oil ball." Even if the oil is cycling between entrained and liquid more will be liquid and less will be aerosol.

Citing people who've had good results and those who haven't doesn't support any argument. I'm reminded that Paul J. got black-flagged off RA with his supercharged car due to oil burning. No scrpaers. So what? I think the real difference is in the amount of wear in the heads.

GlenL

And Sways, when attempting to making comparisons be sure to consider the complete set-up.

Looking at JLPs supercharger thread he is routing the oil from the catch can back into the sump. My set-up doesn't do that. I drain it out as there's water in it, especially on the street.

The bottom line is his usage is absolutely not comparable to mine.

Carl Fausett

When I compare JLA's experience with mine (both supercharged, both at Road America) the difference I see between the two cars is the conditions of the motor.

My motor had 500 miles on brand new rings and have been shown to have not been fully seated yet.
JLA's motor is a stock Euro that he bought and plunked into he car. I do not think he rebuilt it - my point is that it has more than a few miles on it and the rings are very well seated.

I think, when downshifting into a corner, and the oil flys forward in the pan plus you are perhaps engine braking a bit, that is when crankcase pressures hit their peak. At this moment, the quality of the seal of rings is critically important.

GlenL

Carl,

Are you draining the catch can back into the sump?

Carl Fausett

Those comments from Marc Thomas about the amount of oil in suspension at any one time do not fall on deaf ears. He makes some good points.

But, as Glen says, (and Swaybar has pointed out) there are so many different variables that it is VERY hard to compare engine A in Car B driven by driver C with any other.

The CW is, however, that crank scrapers provide 3 benefits: they reduce the suspended oil wind, the lower the temperatuire of the oil, and they reduce the amount of missive air in the oil (that leads to bearing failure).

I'm thinking that we are pushing the 928 into areas where the factory did not take it - as they only very briefly raced this motor themselves. And without boost.

It would seem that "half-way" is the mistake.... either you go scraper-less like some do and design catch can for 1 qt every 30 minutes or so.... or you go crank scraper/windage tray etc but you must now design to deal with higher sump volumes.