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With my late 90S4 I found there was a magic rpm number where oil consumption went from marginal to **** poor- that number being somewhere around 3500 rpms. After I lost the S4 I purchased my current GTS knowing the motor was TBF'd but having the S4 lump to put in the GTS chassis.
The big whopsee was fitting the GTS breather system to the S4 motor as oil consumption suddenly increased. Resigned myself to trying to fix the problem and moved to a revised breather design fitting a Pro Vent separator and a John Kuhn designed baffle with wire mesh inside the unit. I also utilised cross over pipes from the two cam banks. The design failed for reasons unknown. I wondered if John's baffle had too much hydraulic resistance- posted about my frustration and then Tuomo suggested a simple modification. It was a shot to nothing but after fitting such mod the oil consumption improved dramatically. I also collected oil from the Pro Vent in a sealed catch can to test for how much oil the Pro Vent was collecting and there was little more than a wetting of the screen. I figured that John's baffle was taking out all the removable oil so dumped the ProVent altogether and plumbed the vent pipe from underneath my filler neck directly back to the inlet via two hoses. Now I do not notice oil consumption any more. I concluded that John's baffle design and the Pro Vent are not a good combo.
To be fair, I no longer drive the car like I used to mostly for legality reasons [too many speed cameras] but still work the motor when I reasonably can. As I suspect most of us now know, the stock breather systems are crap and some more than others. Just wished I had modified the stock GTS filler neck instead of the S4 item but given I have no intentions of going back to the stock system it is somehow irrelevant.
Are you aware of an engine from another company that uses the undrilled design?
Mazda Miata comes to mind.
I’m sure there are others, I just have looked a little bit into the Mazda four cylinder rotating assembly because it’s got similar main journal sizes and similar crankshaft oil drillings 928, yet spins over 8000rpm without any oiling problems.
Dave, You have posted some great data in defense of your position and I agree with the points you make, BUT, don't S3s have a 2.20 rearend? And basically 70% of those manufactured are AT?
I appreciate your thoughts.
Seth has a Rogerbox. It's in his sigline.
Originally Posted by worf928
...What's different? Average rpms. One might argue that the GT has a tad higher compression that might contribute.
The theory - my theory - is that the higher average rpm for GTs lead to - on average - more oil getting whipped into foam that fills the heads' oil returns thus making poor crank case ventilation worse when compared to an S4 w/2.20. And that is what 'helps' oil ingestion via the breather system...
One very interesting discovery I made on my roadtrip to California was oil consumption as related to average RPM. 85 S2 5 speed (16v M28/21 motor). Running 'slowish' (between 70 and 80) used almost no oil. Running a bit faster (80-85) used maybe a half quart of oil per fillup (about 3/4 tank). Running 'fast' (85-90) used a bit over a quart per fill.
Admittedly, 16v & 32v motors are quite different, but I think the overall idea is sound.
Originally Posted by GregBBRD
...I absolutely love that Porsche was replacing GTS engines, under warranty, for excessive oil consumption, and no one bothered to take one apart and figure out why!
I always try to remember that 50% of the mechanical engineers out there, finished in the lower half of their class.
Judging from the engineering "flubs" that they have had on almost every model, Porsche hires them, by the busload.
By that point, the writing was on the wall for the 928. It was enough of a 'lame duck' that they weren't going to put much, if any, effort or money (mostly money) into R&D on it.
And George Carlin had a bit about the idea that somewhere in the US is the 'worst doctor in the country'. And that someone has an appointment with him today.
GTS engine has many problems, including the longer stroke making crankcase gas flows harder to manage, bad crankcase breather design, too wide piston rings, too much oil on the bore walls, a bad oil gallery design (same as for earlier models), inane center counterweights in the crankshaft, etc. I think a lot of designs and materials got worse since ‘87.
Wow, this has turned into quite the thread...
Gentlemen, thank you all for your responses, and for the depth of knowledge on this board!
Bottom line, I AM concerned about oil consumption in my Red Witch. Yes she is an S3, and is only 'low RPM' with a Rogerbox and 2.20:1 final drive. However, I want to be able to wind the tach to 6000 whenever the mood strikes me. I have seen the sea of oil in the outer plenums on my 'good running' S3 before I took it apart. I didn't like it. I already have an ancient Devek oil filler baffle, the GB oil filler baffle, and the GB cam cover baffles. Assuming I can afford it, I have no problem spending the money for the GB windage tray if there is a benefit to MY 928.
Based upon what I have read, I think there will be a benefit to running the windage tray in my S3 engine. Granted, it will not be as beneficial as it would be in, say Ken Rudd's Mossgreen Metallic track day S3, but it should help. And, the engine is already apart and mounted on a stand in my shop. No better time to install it.
I have e-mailed Mary Lou at Precision Motorwerks for a quote on the windage tray.
Thanks for taking the time to answer my question!
P.S.: Sorry it took so long for me to reply. This has been a particularly FUN weekend at work. We had a broken tooth go through the 5' diameter double herring bone intermediate gears on a 2000-ton mechanical press. We have pulled the shafts and are replacing the gears. A little larger scale than I am used to working on...
That hurt... Just rigged the shaft out of the intermediate gear.
GTS engine has many problems, including the longer stroke making crankcase gas flows harder to manage, bad crankcase breather design, too wide piston rings, too much oil on the bore walls, a bad oil gallery design (same as for earlier models), inane center counterweights in the crankshaft, etc. I think a lot of designs and materials got worse since ‘87.
Looks like Greg weighed in on the S3 question. The few S3s I've worked on had ton's of oil - like Greg posted - in the intake plenums. So, oil ingestion isn't just an "S4 thing."
USA S3s had 2.20s. RoW S3s did not.
I never realized there was an actual RoW S3. Thank you all.
The S3 breather system is essentially the same as the early S4 and they share the main features from the same patent.
The easiest way to improve on that design is to swap the lines such that the engine breathes out from the front under acceleration and from the rear under deceleration. Baffles etc. also help, but that’s the most important change in my opinion.
Ultimately it all depends on how hard you plan on driving the car...... Track days or Open Road Racing, then its required...occasional spirited driving and cruising...not as important as long as you keep a sharp eye on oil level.
However if you any reason you have the motor out, can't hurt to install windage trays and a pan spacer plus improved breather as cheap insurance. On my 1984 Lemons racer I ran the original "OB" pan with 3/8th spacer and I just routed the stock breather to atmosphere, since I didn't want oil back in intake increasing knocks on a raced engine. At the end of a day there would be a bit of oil in the separator vented to atmosphere, but not bad and she only burned about 1/4 qt per hour on track....
My bad. I guess, technically - in Rennlist Speak - RoW ‘85s and ‘86s are still S2s.
Keeping in mind that S2, S3 are monikers we’ve bestowed on 928s between S4s and those without duck tails.
Well, the S2 is an official Porsche designation. Although it was only for cars sold in the UK. 84-86 with the twin dizzie M28/21 & 22 motors. The same car was sold in other RoW markets as the "S", but it's the virtually identical (except the placement of the steering wheel) and a lot of people call them "S2". I have an 85 C00 German delivered car that was federalized. It's easier to call it an "S2".
And although the "S3" was never an official Porsche designation, it's logical that the first 32v cars, with the "pipe organ" manifold are called that. coming both during and after the S2 and before the S4.
There were 32v 'pipe organ' cars sold in a few of the RoW markets. I think Australia got them in 86. Maybe Switzerland too.
With my late 90S4 I found there was a magic rpm number where oil consumption went from marginal to **** poor- that number being somewhere around 3500 rpms. After I lost the S4 I purchased my current GTS knowing the motor was TBF'd but having the S4 lump to put in the GTS chassis.
The big whopsee was fitting the GTS breather system to the S4 motor as oil consumption suddenly increased. Resigned myself to trying to fix the problem and moved to a revised breather design fitting a Pro Vent separator and a John Kuhn designed baffle with wire mesh inside the unit. I also utilised cross over pipes from the two cam banks. The design failed for reasons unknown. I wondered if John's baffle had too much hydraulic resistance- posted about my frustration and then Tuomo suggested a simple modification. It was a shot to nothing but after fitting such mod the oil consumption improved dramatically. I also collected oil from the Pro Vent in a sealed catch can to test for how much oil the Pro Vent was collecting and there was little more than a wetting of the screen. I figured that John's baffle was taking out all the removable oil so dumped the ProVent altogether and plumbed the vent pipe from underneath my filler neck directly back to the inlet via two hoses. Now I do not notice oil consumption any more. I concluded that John's baffle design and the Pro Vent are not a good combo.
To be fair, I no longer drive the car like I used to mostly for legality reasons [too many speed cameras] but still work the motor when I reasonably can. As I suspect most of us now know, the stock breather systems are crap and some more than others. Just wished I had modified the stock GTS filler neck instead of the S4 item but given I have no intentions of going back to the stock system it is somehow irrelevant.
I have one of John’s baffles. What was the simple mod? Was it to the baffle or something else?
01-13-2020, 06:22 AM
