When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've pondered and farted around with this whole crankcase vent issue; and over time I've come up with a simple solution.
Replace the oil filler cap with a cut piece of foam to fit into the oil filler opening. Cap off the port from the AOS to the turbo compressor. You now have an independant crankcase vent to atmosphere, where you leave the oil filler cap off, and the crankcase vents through a huge opening (the oil filler neck), but the foam traps the oil vapour. Any crankcase pressure escapes instantly and the intake track, including IC, remains squeeky clean (catch cans still let oil through, somewhat)
I'm all about function before form.
Is it redneck; yes.
Is it effective; very
Originally Posted by V2Rocket
you should *only* drill the AOS if fitting a catch-can+breather tank combo.
drilling the AOS will drop the AOS's efficiency to the point where it can no longer S the A and O...
at that point you are using the "AOS carcass" to merely contain your oil leak, and relying on the catch can to remove oil vapor and the breather option to drop crankcase pressure.
Yep, aware of that, but moot, since I'm not doing it.
I agree you should have a catch can if you drill, but have to say I catch surprisingly little oil in the can even after drilling the AOS.
Tom, do you have the can routed back to the maf tree or to a can vented to atmo? Also have you noticed any difference in the amount of oil in the can in relation to oil level?
Tom, do you have the can routed back to the maf tree or to a can vented to atmo? Also have you noticed any difference in the amount of oil in the can in relation to oil level?
/Peder
It is routed back to the J-Boot yes. It seems to do a good job of trapping the oil and keeping it out of the intake (better than the AOS alone for sure). As for oil level, my motor doesn't use much (knock on wood) so I rarely have to add oil between my very short oil-change intervals. I haven't seen any relationship between the amount in the can and the amount in the pan. There just isn't that much oil in the can to detect on the dipstick. I drilled the AOS due to excess pressure, not excess oil coming out of the AOS, so cars that are blowing out a lot of oil from the AOS may have different results...
It is routed back to the J-Boot yes. It seems to do a good job of trapping the oil and keeping it out of the intake (better than the AOS alone for sure). As for oil level, my motor doesn't use much (knock on wood) so I rarely have to add oil between my very short oil-change intervals. I haven't seen any relationship between the amount in the can and the amount in the pan. There just isn't that much oil in the can to detect on the dipstick. I drilled the AOS due to excess pressure, not excess oil coming out of the AOS, so cars that are blowing out a lot of oil from the AOS may have different results...
Ok Tom. On the hose between the AOS and your Catch can do you have that small valve present as on the stock hose?
OK, I am finally getting around to making my stock '86 951 faster, which will also include testing different breather configurations.
Charlie at Evergreen built me a trick hybrid turbo that uses the factory K26 center section, so I will be retaining the original turbo oil drain/mount system, but will incorporate a closed Saikou Michi catch can between the factory AOS and J-boot.
However, I will also be running a VEMS standalone engine management system with speed/density airflow measurement (MAP sensor, no airflow meter/MAF sensor of any type), and as such the J boot will basically be an open intake tube attached to a modified factory airbox. So, there probably won't be much of a vacuum in the J-boot at idle, but I will test this.
If the vacuum in the J-boot at idle is insufficient and/or smoking occurs, this is where the two-way system with check valves comes into play. Several of you postulated various renditions of this idea, and I mentioned how the Porsche factory does it in their modern cars in a previous post:
Though the fittings are huge, I will test this out using a check valve assembly from a first-gen (2003-2006) Cayenne Turbo:
The upper fitting is the inlet from the valve cover/crankcase (the Cayenne bank 2 valve cover has a pressure regulating valve built in). The outlet at the right connects to the intake manifold, downstream of the throttle body; during idle and light load/cruise situations (vacuum present in the intake manifold), the crankcase gases are vented here. Any boost/positive pressure in the intake manifold will cause the right-side check valve to close, and the crankcase will be vented to the turbo inlet hose (J-boot of the 951) where there is low pressure (the left check valve in the assembly is closed when there is vacuum in the intake manifold).
Now, the fittings on this are huge as the breather system has to support airflow from a twin-turbocharged 4.5-liter V8. Even a modified 951 likely does not need that much flow through the breather system, but I happen to have this lying around and its configuration is handy for testing purposes.
Of course, exposing the intake manifold to the crankcase via a large port results in a large unmetered air leak as mentioned earlier in the thread. As I mentioned before, the Cayenne (and most other factory German breather systems) use a crankcase pressure regulating valve (basically a fancy PCV valve with a spring-loaded diaphragm) to regulate flow from the crankcase. Other systems (such as that of the twin-turbo BMW N54 engine) merely used fixed orifice tubes to limit the amount of flow from the breather system to the intake. Fun fact: the check valves of the N54's two-way breather system are built into the valve cover, so if one of the check valves fails, the entire cover needs to be replaced!
Anyway, as long as this unmetered airflow is regulated/restricted in some manner, it shouldn't affect the operation of a speed/density system as much as it would a system that directly measures airflow.
I should be getting the VEMS system installed in the next week or so, and before that I will test the crankcase vacuum/pressure of my otherwise stock engine and monitor any changes with modifications and report back here. My engine does have almost 170K miles on the original bottom end and is getting tired (gonna rebuild one of my spare engines to replace it), but it runs great and has a leak-free intake system and should provide a good indicator of how the factory designed the breather system . . . .
been thinking about crank pressure and also oil separation recently and remembered this thread...
food for thought to maybe spur further discussion:
1) the stock 968 AOS hose dumps just in front of the throttle plate (atmo side, not manifold side)
---- relevant because people in this thread were wondering about vacuum or lack thereof with a MAF setup rather than stock AFM/J-boot.
-------- my theory is that this location is still sufficient to get the vapors carried into the manifold/engine by in-rushing air regardless of throttle position, and that the AOS system only seeks to equalize crankcase pressure with atmosphere (so any excess pressure inside gets routed to the TB)
2) if someone were in an experimental mood and wanted to check vacuum in a MAF/MAP setup pre-turbo perhaps a good way to feed oil vapors back into the system would be a carb-style venturi...give your AOS an annular booster
Bump. There are so many threads that reference the turbo catch can, so I just kinda picked one randomly. What's the best solution for a guy that's not DIY? I just want to give my Indy an easy to install and easy to drain, check each oil change kinda thing. What's the easy peasy bestest option in 2018? Thanks in advance.
Just finished reading through this entire thread. Don't recall if anyone suggested this, but why not use a vacuum pump? I think it would help suck the oil through the turbo drain. I just picked up one to assist with turbo drainage (and hey if it improves braking, then that's wonderful). I scored one that looks identical to this for $200 US.https://www.speedwaymotors.com/SSBC-...ump,50355.html
Belt driven is the way to go, that way you can select pulleys to customize the vacuum.
Vendors that specialize in these will also have an option to limit max vacuum via a pressure relief valve mounted at the valve cover (S, S2, 968) or cam housing threaded plug (T and NA).
You have to be careful here and know what you are doing.....too much crankcase vacuum from a pump can rob lubrication from piston wrist pin and rod small end bushing.
T
Originally Posted by Noahs944
Just finished reading through this entire thread. Don't recall if anyone suggested this, but why not use a vacuum pump? I think it would help suck the oil through the turbo drain. I just picked up one to assist with turbo drainage (and hey if it improves braking, then that's wonderful). I scored one that looks identical to this for $200 US.https://www.speedwaymotors.com/SSBC-...ump,50355.html
Interesting, T. That's good to know. Any recommendation on an ideal vacuum value? I think this kit comes with a switch to only turn on when it detects pressure.
The one you showed is an electric motor driven diaphragm pump..? Probably won't last long.
If your car duty is rally, off road, you can just run a venturi into your exhaust pipe stream with an old 80's one way pollution AIR pump diverter valve to check decel back flow.
Assuming you deleted or are willing to delete your cat, oil residue in the scavange would certainly clog it.
T
Originally Posted by Noahs944
Also, is there a suggested way to run a catch can on a turbo'd engine if still running a closed system with an auxiliary vacuum pump?
Thank you for the suggestions. That old school scavenge is tempting. I absolutely love how simple it is. I have opted to run 3" high flow cat(s) on the car as a courtesy to other cars on the road.
My research is showing 8 inches of vacuum is about perfect. Thank you for mentioning the bearings being starved for oil... I had no clue & certainly don't want that headache! For those with any interest in an electric vacuum "booster" pump, you will need a trigger/switch to shut it off once at the ideal pressure or negative pressure. This 700r4 transmission switch is adjustable from 6-22 negative pressure, is designed for a 12 v system and can be used on a normally open or normally closed circuit. This will be used to turn it off but the pump comes with a switch to turn it on when it senses pressure. I will be using a boost gauge to monitor crankcase pressure and also install an led dash mounted light to monitor when the pump is running.
02-16-2017, 11:46 PM
