Oil filler neck
 

When did they start with the Oil filler neck with the vent on the side, rather than down by the baffle? GTS?


https://cimg0.ibsrv.net/gimg/rennlis...48bfaea87.jpeg

My 928 GTS has that filler neck but my late 90S4 did not- neither do the 91 S4 models AFAIK.

The filler neck is listed in PET from 92, but the hose connecting to it from 93...

Yes, GTS, although there are a couple of different versions of that style filler neck.

So, if I fill oil a bit goes into the hose and into the intake...

Yup.

Yours is probably the early one with the hole through the hose attachment wide open.

The later version has a tiny hole in it, in order to restrict the amount of oil that can pass through (it also restricts how much air can vent out of the crankcase....that was a terrible idea, too.)

Modify a funnel with a long neck that inserts past the opening.....that will fix your immediate problem.

Yes, mine is from a 92’ GTS. Wide open.

Did a few tests of this. Shocking design.

Whatever you do do not do what I did 14 years ago when I fitted my S4 motor into the GTS chassis- I converted the breather system into the GTS format so that the motor was visually like a GTS motor- oil consumption increased dramatically!

Then I came up with a modified system and modified the S4 filler neck instead of the GTS filler neck [bad move].-after a few iterations and a subtle suggestion from Tuomo I ended up with my current configuration and it seems to work fine now.

What is your current configuration?

I have vent pots on all four cam cover positions. I have cross over pipes side to side front and rear. I have a John Kuhn baffle in the filler neck [nothing else] and the underside of the neck is modified to permit a bigger vent. Originally I had a 1 inch pipe to the pro vent separator but the thing was not doing anything oil collection wise so I split that outlet into two smaller return lines back to the breather connections on the side of the throttle boot. The subtle modification was a small line that ties into the rear crossover and vents to the connection at the front of the motor that takes the fuel tank breather back into the inlet tract.

Tuomo has a thread where the concept is illustrated.

Any links to this thread?

Is this the thread, Fred? https://rennlist.com/forums/928-foru...l#post16446359

"Shocking" is an understatement.
Porsche did some radical modifications on the '93 ('92/'93) GTS engines to "improve" the breathing/ventilation system....some of which made little or no sense, engineering wise.
In 1994/1995, they "corrected" these errors and made changes....which were worse.

When you "hang your hat", claiming to be an engineering company that also builds cars, stuff like this should be terribly embarrassing. However, even today, with their current record of constant engine "mistakes" they seem to be content being completely stupid.
Apparently, simple logic isn't all that simple, anymore.

I have Greg Brown's oil vents on all four cam cover positions. Plan to mimic the GTS routing. Need to tap a hole in the metal oil filler. I'm going to fashion a 70 degree angle fitting to prevent retrograde oil flow.

Yes- that is the thread - post 19 is where Tuomo introduced his concept - by then my breather system was up and running- a sort of guinea pig as it were. Tuomo had seen a post [or thread] of mine wherein I was looking for suggestions and he came up with his offering that I duly cobbled together. It is quite innocuous and with the Pro Vent now removed a passing glance would not pick up anything that sticks out like a sore thumb. My plumbing was "inventive" to say the least literally using a few small domestic plumbing parts that are masked or out of sight including copper pipe and a couple of Yorkshire fittings not to mention a section of some flexible hard piping. I also used some discarded rubber tubing sections [I always squirrel away stuff I have routinely replaced- surprising how often they come in handy!].

It seems that engine breathing is a critical concept fundamental to engine design and some engines are clearly more susceptible than others to breathing issues. Have you seen another Vee 8 mass produced vehicle [as opposed to limited run specials] that has a bonnet line as low as the 928? I work on the premise that it is this compactness that causes issues and for whatever reason [$$$?] Porsche just did not fathom out optimal solutions. That folks are fathoming out improvements 30 years down the line says something about the seemingly inadequate nature of the OEM design. The S4 system although far from perfect was sort of acceptable but had a pronounced increase of oil consumption above a certain rpm point - probably 3700 as best I could fathom- most 928's cruise at less than that to remain legal. The GTS system is a basket case plain and simple- it had several iterations and non seemed to work presumably something to do with the very compact crank case design and the ability [or lack of it] to breath effectively with the GTS crank stuffed into it not to mention the impact of a longer stroke and piston to crank clearances.