Hi Mark, thanks for the email it was a prompter for me to take a few minutes and get back to this thread. Over the years I have used a suite of fixes for the RB's propensity to pump oil into the inlet system and or catch can. Depending on the condition of the engine and the size of oil pump used, there are a number of things that can be done.
1. Pick the right sized oil pump for what your car is going to be used for. For example if you are doing only daily driver, street work you don't need a Jun/Tomei etc oil pump, a new standard R34GTR oil pump does everything a street engine needs. If you are doing a fair bit of track work then an N1 pump is a worthwhile upgrade especially if you are adding an engine oil cooler . At the same time you should be looking at a larger capacity, winged and baffled sump. In simple terms, if you are doing enough track work to justify an N1 pump and oil cooler then you need a decent sump. If you are doing targa work, drags, lots of launch control and rev limiter use then that’s where I would suggest a Jun/Tomei etc oil pump be used. They better tolerate the hammer action, but eventually even they will fail. We replace them once per year as part of the lifing cycle.
2. Fit the right sized oil flow restrictors , use the table to determine the size and number of oil flow restrictors.
3. Improve the oil flow away from the cylinder head, tidy up the oil collectors with a die grinder, drill out the oil return holes (+1 mm is plenty) and if you are doing lots of drag, targa, circuit work etc then an external oil return is advised. I have a preference, based on experience, for the rear return as it is inertia supplied with oil under acceleration.
4. Make sure the cam cover baffles are in place and in good condition. I see so many RB’s cam covers that have had the baffles removed, possibly for cleaning, that have subsequently not been replaced. The standard RB26 baffles are fairly effective on their own, but I have had some success with adding stainless steel wool stuffed inside the baffle covers. Obviously the wool helps to separate the geyser, into oil and air, with the oil running back into the cam covers and the airflow continuing on to the catch can. For RB20’s and RB25’s I would always use the stainless steel wool as their standard baffles are not as effective.
5. The above items are usually enough except when the engine has an excessive blow by problem. Obviously the correct remedy for this is to fix the problem, find out what’s causing the excessive blow by and eradicate it. If I need a short term band aid then I remove the dip stick and vent the dip stick tube to the catch can. This usually removes sufficient blow by airflow from the sump up to the head such that 1 to 4 above can do their job.
If you have done all 5 of the above and you still have excessive oil flow into the catch can, then the engine has a serious problem that needs to be fixed. The first thing I do is get out my trusty leak down gauge and check the status of each cylinder. My rule for a turbo engine is, if am seeing leak down in excess of 10%, then I seriously consider pulling it and doing a proper inspection and rebuild. Better to catch it while it’s still has some life, than let if die a death filed with mechanical mayhem.
Hope that was of some help
Cheers
Gary