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if you don't want to participate, then don't. apologies if you are angry by my lack of knowledge; I learn
something everyday from this forum and from the wonderful folks who give positive insight. since I can't
be there to extend personally, I will offer this again:
Merchauser -- In your original post you asked if it was okay to ditch the factory ventilation system and simply vent to the atmosphere. As others have commented, until the GTS, the stock crankcase ventilation system worked under most driving conditions. If pressed really hard, the S4/GT engines could have some problems with oil build up in the intake. This was relatively rare. With the GTS engines, that problem became much more common and did not require hard driving. In addressing this issue, Greg Brown (and others) developed baffles that reduced the amount of oil drawn up by the crankcase ventilation system (and permitted oil to more quickly drain back down into the crankcase). This largely solved the oiling issues with the GTS (which also needed changes to their pistons) and the S4/GTS engines. With Greg's oil filler baffle (or another that works), the S4/GT stock crankcase ventilation system works fine and there is not need to change to something else.
That still leaves your question of whether you can bypass it and vent it to the atmosphere? If you don't mind violating federal and state law, sure. It won't provide any noticeable performance improvements and will increase oil consumption. While one 928 running without proper emission controls won't wreck the environment, the requirement that crankcase vapors NOT be allowed to directly vent to the atmosphere was one of the 1st forms of emission control mandated by the government. It was one of the 1st because it produced a lot of reduction in emissions for the cost in terms of performance and dollars. So, the answer to your question is, yes, you could vent to the atmosphere. But it requires a question in response, why would you?
So, the answer to your question is, yes, you could vent to the atmosphere. But it requires a question in response, why would you?
thank you, david, for the insightful response. as mentioned, I am going to keep the stock breather set up and use the GB baffle. for my car, I feel confident, that this
will be the best choice and make for a happy resolution. the only reason I was asking and thinking about venting to the atmosphere, was to keep an crank vapors
out of the intake and TB. thanks again.
after much searching, I still had not found answers that I was looking for. that's why I started this thread. if its old hat for many,
sorry for the redundancy; no one need comment or respond if they are bored or sick of it.
No need for any apology whatsoever- folks are free to post their point of view but to be clear - you owe no one an apology
The subject matter has evolved over the years and I have had advice from very knowledgeable folks that just did not work and some very interesting inputs that were most helpful. My current incarnation is a variant of what I had already developed and although the scheme suggested by Tuomo involved only minor mods on top of what I had, it was one of those things where something relatively simple made quite a lot of difference.
In the end I concluded that the system as installed on your model year is probably the best system Porsche installed on their 32 valve motors. When I fitted my S4 motor into my GTS chassis initially it had the original S4 breather system. I like to work the motor and the simple fact is that all 32 valve motors seemingly lift a lot of oil when worked hard. I suspect this is in no small part due to the compact design of the motor. There seems to be a rev threshold over which the motor lifts oil chronically- Blake suggested 3k rpm and that sounds about right. All stock systems show lots of oil in the inlet manifold when it is removed. I had mine off a few weeks ago and it was spotless- no oil in sight.
The first mistake I made was to convert the S4 stock breather system to the GTS format - that just increased oil consumption. I did this because I somewhat stupidly [with hindsight] wanted it to look like a GTS motor. When that did not work I decided to do something a bit more radical and integrated a Pro vent separator and a baffle in the filler neck. That did not improve things and eventually installed a cross over pipe on the rear cam cover connection points- again no improvement. Then Tuomo suggested his modification and that made a significant difference. My motor still consumes some oil but nothing like the amount it was doing. The second mistake I made was to modify the S4 filler neck- with hindsight I should have modified the GTS filler neck given that system is seemingly awful. The baffle I have used is the one design by John Kuhn. This uses baffles to slow the gas down as it gets thrown up by the crank and then uses crinkled wire mesh to help the oil mist particles coalesce [join together] and when they have done so the bigger droplets can then drain back down into the sump. With this baffle the Pro vent is doing next to nothing and I am thinking about removing the Provent altogether. When fitting this baffle one also cuts out the baffle plates in the bottom section of the plastic filler neck. I also modified the filler neck such that there is a big outlet on the underside of the filler neck that discharges to the Provent- it is a bit of bugger when topping up with oil as I have to use the rubber bung that John supplied with his kit to stop the oil falling into the Provent.
I can well believe that just fitting a good baffle in the filler neck might have worked with no other mods mods to the S4 type system but I had gone past the point of no return as it were - now I am happy with what I have.
I have several different "levels" noof crankcase/cylinder head ventilation, depending on what the car is used for and how it is used.
Since the OP has an S4 engine, I'll concentrate on that engine, here.
The first level (an additional oil baffle under the filler neck) is the very first step and will reduce the amount of oil that reaches the intake system by a huge percentage. Every 928 engine will benefit from this piece.
On engines that are run at higher rpms for long periods of time or on GTS engines (where Porsche essentially "gave up" on crankcase ventilation and relied on the oil return passages through the heads to ventilate the crankcase), the cylinder head drains can become overwhelmed and oil will "burp" up the oil snorkel/snorkels on the valve covers. This oil will reach the intake. To help solve this problem, I do make a "valve cover oil separation kit", which greatly helps with this issue. (Don't bother looking for a picture or reference to thsee pieces....it doesn't exist. I'm extremely careful about who is allowed to see or use these pieces....I'm very tired of people stealing and copying my stuff.)
The next level up....engines that are frequently used at high rpms (and for the GTS engines) it was necessary to change the plumbing and "add in" a Provent/oil separator system. The Provent version is used on engines that are still viable and have adequate piston rings. Badly deteriorated GTS engines that have "killed" the rings can overwhelm the Provent and I change those engines over to an extremely custom oil separator.
For competition engines/severe street, I have a "stand alone" head oil evacuation system which actively removes oil from the cylinder heads.
And for full out competition engines, I have a complete dry sump system with head oil evacuation.
All pieces/systems, with the exception of the full out competition engine system, are closed crankcase pieces/systems. The last year that open crankcase ventilation was legal on a street vehicle was 1957....I was alive then and know exactly why that law was passed....the air was terrible!
I have several different "levels" of crankcase/cylinder head ventilation, depending on what the car is used for and how it is used.
Since the OP has an S4 engine, I'll concentrate on that engine, here.
The first level (an additional oil baffle under the filler neck) is the very first step and will reduce the amount of oil that reaches the intake system by a huge percentage. Every 928 engine will benefit from this piece.
...
Greg -- How much does the oil baffle under the filler neck cost and is it something the average owner can install on his own?
Greg -- How much does the oil baffle under the filler neck cost and is it something the average owner can install on his own?
What year car?
That kit is $150, with new O-ring (for '87 and later cars) or a gasket (for earlier cars.) Includes a tube of Drei -Bond (which you will use about 1/8 of.)
The filler neck and the water cross-over need to be removed. There's another thread going about how to remove the water cross-over without removing the intake manifold, on a late car.
One thing to keep in mind if you use a Provent is that you want to have the large droplets of oil removed from the blowby gasses before it reaches the Provent. You only want it filtering the fine mist/ oil vapors from the crank case.
If too much oil reaches the Provent it will essentially "clog" because the filter got overwhelmed. This increases crank case pressure and bad things can happen.
If you install one make sure to have a baffle installed before hand or block off the large oil filler ports on the filler neck to keep oil from getting into the hoses from the cylinder #2 counterweight.
The homebrew system on my 89 is essentially a modified version of the Sharkvent system from 928 Specialists. But it is closed case (it was stinky when running open) and has a GB modified dipstick tube for a drain.
Whatever you do make sure you mitigate large oil droplets from the crank. This will give you the largest gain in oil control performance.
That kit is $150, with new O-ring (for '87 and later cars) or a gasket (for earlier cars.) Includes a tube of Drei -Bond (which you will use about 1/8 of.)
The filler neck and the water cross-over need to be removed. There's another thread going about how to remove the water cross-over without removing the intake manifold, on a late car.
Thanks, Greg. My S4 is a 1990, as is the GT of the original poster. I thought it would help if those reading the thread had some idea of the commitment we’re discussing. $150 plus a few hours time seems like a good investment.
Thanks, Greg. My S4 is a 1990, as is the GT of the original poster. I thought it would help if those reading the thread had some idea of the commitment we’re discussing. $150 plus a few hours time seems like a good investment.
Certainly the most "bang for the buck" of anything I offer. Although oil still makes it to the intake, the volume is greatly reduced.
To completely eliminate oil getting to the intake on a street S4/Gt/GTS, it takes a bunch of pieces and some much bigger $$$.
Of course, once all the incoming oil is eliminated, the carbon is knocked off, and they are tuned, the engines run better than any other $$$ one can spend.
Oil in the intake system is a terrible thing to do to a 4 stroke internal combustion engine. Effective octane drops, carbon forms, compression goes up, the knock sensors pull timing, and the over rich mixture kills performance.
06-01-2018, 12:59 PM
