Alan

I have been posting in DR's Sharkvent Post about my plans for a custom Provent/Sharkvent install.

In order not to dilute any further DR's showcasing of his production Sharvent systems I decided to create a seperate thread. Not least because HermanK who also owns a '94 GTS has expressed interest in doing a very similar or even identical install.

I'll repost some things from the other thread for context too.

My goal is primarily to solve the GTS oil ingestion issues - which are pretty severe on the GTS - even in normal (for me) street driving. I do drive the car hard but not excessivly so and see that I burn about a quart of oil every 300-600 miles. I consider this to be way excessive - having to carry several quarts of oil for a 1000 mile round trip is embarrasing...

I have found some good documents on how the stock GTS system works

I have also read lots of details on what folks have done to improve this (especially Louie Ott) and even on what Porsche did on the later models to attempt (unsucessfully apparently) to solve the problem.

It seems that the increased stroke of the GTS significantly worsened a problem that earlier 928's exhibited under extereme conditions (track/ supercharged etc)

Porsche did make some changes - moving the crank porting further up the filler neck, adding a balance vent between the cam covers and fitting a shroud to the cam cover PCV vent but these relatively minor changes didn't help much.

Louie has a compelling argument that you need a bigger vent and active oil seperation from the main crank vent under the oil filler. He also notes that the PCV venting from the passenger cam cover is problematic since that cover tends to accumulate oil/mist thrown up from the crank and the PCV venting runs counter to oil drainback via the same passages.

DR has created a great kit of parts for various model years and many have reported success with the base systems (ROG100, Sterling). However since I was to be removing the intake and cam covers for powerder coating - I had some options that DR just couldn't buld into the base systems (and expect to sell many).

I decided I could easily port all 4 possible ports in the cam covers. I could also modify the oil filler neck and install a crank vent baffle/filler scrubber system an evacuation port and block off the current PCV vacuum ports.

This concept gives 3 stages of seperation:
1) The 928 Intl Oil Control Plate (baffle plate) down in the crank vent hole
2) A stack of 5 copper scrubbies up the vertical (+horizontal) oil filler neck
3) A provent Air/Oil seperator to follow these evacuated solely from the filler neck.

The Provent drains back to the sump and in fact uses many of DR's Sharkvent parts: mounting bracket, dipstick oil drain back with check valve, various fittings and tubes - thanks to DR for being very flexible on ordering custom Sharkvent parts.

For the cam covers the general idea is to make all 4 ports fresh air inlet ports only. These will be plumbed to the intake airbox below the filter and fed via check valves.

This way the flow is always down the head oil drains in the same direction as oil drain back. Its either fresh air sucked in to the cam covers & down into the crankcase or its head blowby forcing its way in the same direction (down the oil drains).

In order to have ~constant flushing the provent output is scavenged by a combination of all the stock intake PCV vacuum ports, some requiring check valves and/or stock equivalent fixed orifices.

Since its possible the stock system has insufficient total breathing capacity I also expect to include a blow-off after the provent into the airpump feed.

This is the plan - pictures of progress so far to follow.

Alan

svp928

Good plan, Alan.

Tom in Austin

Cool stuff, look forward to what you find out. Mobil 1 at $6 + a quart is expensive stuff to burn up needlessly ...

bd0nalds0n

Hasn't it been suggested that the copper scrubbies can cause more problems than they solve?

FWIW, I put on Ole's oil control plate with a 1" hose vented to atmosphere, and I've got no oil out of it with multiple 10-11 psi WOT runs for sharktuning purposes.

While the GTS may have its own set of issues, I think you'd find the 1" line coming off the oil filler neck will help a lot.

I thought some of the GTS oil issues had to do with the fact that the pistons weren't drilled to permit oil scraped on the up stroke to drain back into the lower part of the cylinder/crankcase, but instead forced it to be combusted.

Gary Knox

Alan,
Nice work, and I plan to follow your procedures - for my '89 5 spd track car which uses about 1 qt of oil per day (~125 miles). I rev it to ~6800 rpm about 3-4X per lap, or ~100X per day. It has 125K miles on it.

With respect to the GTS oil burning "problem". I don't know about other "later model" GTS's, but my '94 does not use but about 1 qt in 3500-4000 miles. Maybe it is unique, or maybe they changed enough in '94 to reduce/eliminate the oil burning problems.

Thanks, and look forward to seeing your "solution".

Gary Knox
West Chester, PA

Lizard928

I used steel wool for my system, and made my own air oil seperator which worked perfectly.

Vilhuer

I'm building sort of hybrid of Alan's setup to automatic. All four valve cover holes have factory plastic tube in them. Both holes in drivers side head will get fresh air feed through air pump filter. Both holes in passenger side and oil filler are connected to Mann Hummel. Will have to see how it works. Might add one way valve to fresh air feed if needed.

danglerb

Do the copper scrubbies have some kind rubber band inside them?

Herman K

Gary what is your vin number and the oil you are using. I intend to follow most of Alan's procedure to see how things will compare when done. I'm using 5W-40 versus Alan using 15W-50

Alan

Gary - mine & Herman's are both '94's also - I think you just got lucky - It does seem to be very variable (or maybe we are much more agressive - nah - you just got lucky ).

Here is the Provent/'sharkvent' kit I got as a custom order from DR (thanks DR ).

So contents are the Provent, mounting bracket & hardware, the dipstick oil drain tube & check valve (pre assembled), the main Provent input hose (special version dave found for my alternate oil filler venting), assorted hose clips, Several 1/2" elbows & T's*, the sharkvent extreme filler vent adaptor* and a 1" to 1/2" reducer.

* these are items that in hindsight I probably will need in a different mix - I'll confirm later.

Alan

Alan

Here is a view of the cam covers back on after powdercoating and the addition of the 4th cam cover PCV vent port. Note that all the vents have been angled - this is primarily for cosmetic reasons (new colored lettering is planned)- there is no functional advantage/disadvantage. Since the cam covers have a small indexing tab and the vents have an index slot in the skirt - a new slot was milled in the skirt to facilitate locking at the new angle. They are shown temporarily capped.

Oh and doesn't the "V" look pretty all shiny & oil free like that...

Alan

Alan

Here is a sequence on the filler vent mods.

Note the 928 Intl Oil Control Plate (baffle plate) that goes under the filler neck in the main crankcase vent. I have modified this to expand the total intake area - drilling a few extra holes in the filler bottom and creating some secondary 'deflector wings' to protect them.

The oil filler has been opened up significantly inside the lower housing to take more advantage of the side chambers - the support ribs still exist and are functional but no longer get in the way of flow at the ends. The 5 pure copper scrubbies are high strength types and (3) go all the way up the neck and even around the top a little - as well as (2) spanning the whole filler bottom. The stock filler bottom plate was drilled off its glued on attachment points. The oil control plate has the stock old style filler gasket (+rtv) underneath and a new o-ring seal on the top.

Alan

Alan

This may be partly true but the vast majority seems to be sucked into the intake as evidenced by the puddle in the throttle body.

Roger & Jim have also seen good results with DR's std system (see DR's thread) so clearly its solving the biggest part of the problem anyway.

Alan

Alan

Looking at and testing the Provent I can now see how both relief valves work. The intake side of the filter is vented to atmosphere via the cap vent with about a 10 PSI crack pressure while the filter outlet side is vacuum limited to no more than about -10 PSI (wrt atmosphere) at that point the outlet limits the internal provent vacuum dropping lower. On the outlet side the pressure valve is referenced between the provent internal post filter and atmosphere but the actuator limits flow between the outlet & the provent lower body (post filter).

Net effect is that the Provent Relief valves will not allow high pressure build up before the filter (limited to ~ +10PSI), It will also not allow intake vacuum on the provent outlet to cause the provent filter (and then crankcase) to see vacuum levels in excess of ~-10PSI.

In an open loop system (most of DR's proposed systems) the vacuum relief valve has no effect - but in a closed loop system - like mine (its at least a pseudo closed loop system) it is operational.

Essentially my proposed system is emissions legal. Only if blowby is excessive (more than the intake vacuum can handle) does the system ever vent - and even then it should vent into the exhaust via the Aux air pump not just atmosphere.

For the Provent to vent to atmosphere something would have to have gone wrong...

Thanks to Aryan for the below photos

Alan

Alan

Filler venting plan:

DR has the extreme vent ported into the bottom of the Oil Filler right under the cap. This location is easy to drill out with the Filler in-situ (while keeping the debris out of the engine). However it leads to some difficultly filling with oil. Some of DR's pictures of the extreme vent below for context.

Dave does now have black fittings (see my earlier pictures) which do look much better.

However with the filler neck out I decided to try porting to the top to avoid oil filling issues.

First trial Rev#1 was functional but the lift was too high - interference with the crossbrace. My Rev#2 is much lower and clears the cross brace - but not by enough for my comfort. I don't have a picture of this Rev#2 yet - but I'll snap one soon.

With the engine able to lift up on the mounts a little I don't want the filler neck getting compressed - so I'm on to Rev#3 to try to gain about 5mm more clearance... parts on order.

Herman - hopefully this gives you a good idea about the options for the filler neck porting - seemed I had difficulty explaining what these options were... drilling & porting where mine is would not be practical with the filler on the vehicle - debris will end up in the crankcase... plus you really do need to do this location on a drill press - ideally with a (sacrifical) forstner bit.

Alan