Rob Edwards

I'm not driving my car very often, have only put about 11,000 miles on the stroker motor since 2010. And it's all street use so not much prolonged 6000 rpm use, though there's plenty of _transient_ 6000 rpm use. My intake is dry and my oil consumption is negligible- hard to quantify. I'm quite overdue for a timing belt and will be digging into it soon to do that, will get some pics of the lower plenum.

Andy G has a great deal more miles on his stroker with the oil control setup (I want to say about 30,000?), hopefully he'll chime in.

Kevin in Atlanta

Does anybody have a picture of the grooved bearing shell?

merchauser

earlier in this thread someone mentioned venting directly to catch cans and completely bypassing any venting into the intake. in doing this, does that completely eliminate
ANY oil getting into the intake? is the main reason for the factory system, and for this specific scavenging set up, to be environmentally compliant?

andy-gts

I am puttijng between 4 and 5 k miles per yr on the car, so far 33k since I took delivery and I swear no oil use over that time, now when I did the sand hills event in nebraska that was slow curves and wide open throttle over and over and after 45 min I found the oil on stick down about an eight of an inch......I have done this 3 yrs now, no time to take 14 days off to the the orr in nevada.....I have dome texas mile twice and just love putting foot to floor and hi last time 176 in the last event. Still wish ORR so I can stretch its legs but .......need a new job where I can actually take vacation and not hurt my partners....!!!!!

Greg built a beast of a machine....

jorj7

I run my oil breather hoses into catch cans. One for each side.



I use to collect about a pint of oil per Open Road Race. In 2013 installed Greg Browns modified cam covers and oil fill baffle. I've run 6 Open Road Races since then in the 170 and 180 mph average classes and have only a few drops of oil in either catch can. More photos: http://928.jorj7.com/breathers/

Routing the breathers into the intake is basically for environmentally compliance, as you asked.
__________________
George
90 S4 Grand Prix White (Murf #5 - 210 mph top speed)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

Thom

Rob, Andy & George - thanks for your feedback.

Whilst the stock breather system may be closed for environmental reasons I believe it is also purposed to reduce, at least partly, crankcase pressure.
Evaluating the actual performance of the stock breather system may be difficult if it gets saturated early on, on a [TPS%; RPM] map, as oil is being thrown up into the oil fill tube by the crankshaft.
If an oil fill baffle is effective enough to allow the two breather hoses (between the oil filler and the intake) to bleed dry crankcase pressure into the intake then under most running conditions oil vapours may not be pushed to detrimental amounts up through the hoses out of the cam cover(s). However, as some (such as Louie Ott I think) have observed in the past, these 2 hoses seem severely undersized and do not allow the breather system to provide as much vacuum to the crankcase as needed.

Whilst a scavenge pump has here been proven to work effectively it still seems to be a palliative solution that does not address the 2 root causes, which are excessive crankcase pressure and oil aeration, which each seems to contribute to each other.

Porsche built a crank scraper into the sump of the 968. I read some concerns on here that using a crank scraper on a 928 may starve wrist pins from oil lubrication. Perhaps oil squirters should address this concern, as Porsche also fitted squirters to the 968 block, and the 968 is arguably the most reliable stock engine in the 4 cylinder range, even including the dreaded rod #2 failure.
At this point I am curious to hear if anyone on here have done any sustained high rpm testing on a 928 S4/GT which would deviate from stock with only just the 5 following mods:
- an oil fill baffle
- plugged cam covers
- "larger" breather hoses routed back to the intake
- oil squirters
- a crank scraper

merchauser

in the above photo of the sharkvent, the hose from the oil filler port to the throttle body Y connector is capped off. when I installed the GB baffle, I also replaced my plastic oil filler with a metal one,
along with the required check valve for that port. does the crankcase create sufficient pressure to blow gases past that valve, or does that valve require the vacuum from the TB. wondering about any danger blocking off that hose might create if CC pressure naturally gets past that valve. thinking it must not be a big deal, or that hose would have been routed back to a Tee with the RH rear cam cover vent

Thom

As the throttle is abruptly closed whilst the engine is spinning "fast enough", the resulting spike in crankcase pressure is bled through the pressure relief valve located at the base of the oil fill tube - at least this is the theory and why the valve was put there in the first place. However, as the rest of the breather system is undersized relatively to how pressure builds up in the crankcase within the [TPS%; RPM] "load" map, the switch points (or line) on this load map where vacuum within the breather system changes to pressure may be located so low that the valve may stay open continuously above that switch line.
If the known excessive and continuous crankcase pressure was under control, then the valve would open only during the theoretical instantaneous spikes of crankcase pressure that should occur only when abruptly closing the throttle. However, in the case of an engine like the 928 S4/GT with a poorly-designed breather system, my take is that this valve makes no difference in how the breather works (or rather does not) as it cannot fulfill its function correctly.

UKKid35

What is the longest continuous time a totally standard S4 engine could be run at approx 6,000 revs before possible oil starvation and intake oil contamination and detonation would become a real concern?

Are we talking seconds, minutes, tens of minutes?

andy-gts

I am sure jorj7 has run sustained high rpm in the unlimited division at orr, much more that autobahn sustained high speed travel.....

UKKid35

Yes, I certainly believe that - but his engine hardly qualifies as Totally Standard with no breather mods

Thom

I did a high speed run on the Autobahn with a stock '87 S4 on Saturday, running the engine in top gear at various engine speeds over 5000 rpm for a minute and holding it for about 10s at 6000 rpm.
I coasted half a minute later to be met with a very strong smell of burnt oil which disappeared after about 5s.
The engine is healthy with no black, blue or white smoke coming out of the exhaust, strong oil pressure, no overheating.
My bet is that oil got sucked in through the intake during the sustained >5000 rpm run, was burning in the cylinders and the smell just caught up when I came to a stationary point when after 5s the excess of oil in the intake eventually got completely burnt as the engine was running at low speeds again.

andy-gts

I guess the short answer is NOT VERY LONG , thats why oil control measures were developed............................

Rob Edwards

Before I had Greg's system on my car I was out hooning around with BC, did a couple of WOT blasts of 20-30 seconds or so before pulling into a place for lunch. Big old cloud of oil smoke out the exhaust on startup. That doesn't happen now with the scavenging system.

buccicone