Oil Catch Can Options

I'm about to finish up installing VF Engineering's supercharger kit on my 2000 996. While fastening the positive crankcase hose to the SC's air duct, I remembered seeing somewhere on a forum the use of an oil catch can . I'm familiar with its purpose, and have done some research. There are a lot of them to choose from (examples: http://store.42draftdesigns.com/Stea...Can_p_289.html and http://jlttruecoldair.com/ZenCart/in...dh08smq80tf1p6 that few p-car owners are using. Anybody have recommendations? What inlet/outlet ID size should I be looking for? Capacity? Would love to hear from some of you that have superchargers. EDIT: Wait... doesn't the "AOS" (air oil separator) handle this task already?

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Answer: Yes that is exactly what it does. New question: Does anyone know if the Turbo 996 use the same AOS or do they do something completely different? Was wondering if the stock AOS is up to the task on a boosted car.

You probably don't need one. But it is an extra step to prevent oil from gumming up your intake. Since you're now boosting the engine, the intake will be more likely to pull oil from the AOS/crankcase under pressure than in n/a form. IMO a cheap eBay unit is fine. You can adjust the size of the tubing by picking up fittings & hose from home depot.

The AOS separates the oil vapor from the crankcase fumes and returns the oil to the engine while letting the new oil free (so to speak) fumes continue to the intake where the fumes are routed to the engine and burned. The 996 AOS is designed to work with a NA engine that has a vacuum at the point the AOS hose connects to the intake manifold. With the addition of a supercharger and the resulting positive air pressure in the intake at least some of the time I'm not sure what's required. The supercharger manufacturer should have some recommendation I would think. The 996 Turbo is a dry-dumped engine. The oil tank (the upper portion of it anyhow) acts serves to separate the oil vapor from what is returned by the oil scavenge pumps. I do not know the differences beyond this. I will note the turbo engine does not make boost all the time and when not making boost the intake runs with some low pressure which will help remove crankcase fumes that have been cleansed of their oil vapor content.

Thanks for the info, guys. For now, I'm going to run the SC manufacturer's standard setup (as pictured above). After the break-in period, I'll disconnect the air duct and see how much oil build-up there is. Will report back in a month or so.

Doug, I wouldnt think you need it either except I suppose its possible the extra crankcase vapor could overwhelm the stock Oil Vapor Separator. Hope you took lots of pics and will be doing a detailed thread on this including results. Not sure I would have the b@#$! to SC the stock HC engine but look forward to seeing your results. Great job!

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The oil build up is a poor barometer in this case. I hear from a number of techs that whenever they expose the intake system the walls are almost always wet with oil, oil that makes it through the AOS. The stock AOS sucks and I don't mean that in a good way. With a supercharger blow by will increase and this can lower the efficiency of the AOS while at the same time putting more fumes (and oil vapor) into the crankcase thus increasing the amount of work the AOS has to do. A better barometer I would think is how often the engine smokes upon startup. It is my belief that this arises from the oil that manages to get past the AOS -- which ain't hard (to beat a dead horse...) -- and collects on the intake walls where it drains down into one or more combustion chambers and is burned upon the next engine start. If you find the engine smokes more often upon a cold start, all other things being equal (other than the obvious difference being the engine now has a SC) then this would suggest to me the AOS is doing an even worse job at what it does poorly at best. But what to do about it I'm not sure. The smoking isn't the biggest problem though it is the most obvious. What I would be concerned about is the risk of increased contamination in the oil from the extra blow by and the likely diminished ability of the engine with the SC and its AOS to remove this contamination. You might want to due periodic oil analysis to see if water and other contaminates are reaching levels that are cause for concern. The first defense against this would be more frequent oil/filter services. If the AOS can't remove these contaminates then you can remove them by draining away the contaminated oil and refilling the engine with fresh oil. You might object to this "extra" work but it is part of the cost of running a SC'd engine and giving it reasonable servicing that SC'ing can bring with it.

May not be helpful but in my mustang days i always kept the closed loop pvc system. One way to stop oil contaminating the intake was to install a one way check valve so the oil could not be sucked in and the PVC continued to do its job. We used to have isues of excessive crankcase pressure until i did the one way system, even blew out the dipstick once! I want to SC the Porsche, but it is the small issues like this that make me think twice, even though the boost is so low. Let us know how you get on, it may be in next years cards.

You can also run a carbureted fuel filter as a separator to monitor blow-by. Super cheap.

^^yup i used this both between the intake and the SC inlet tube and the crankcase and intake. Works great to monitor the situation!