Best oil for air-cooled Porsche
After a lot of research, here’s my conclusion on the best oil for a Porsche 914-4, and most other air cooled flat-tappet engines. It really does make a difference.
Brad Penn 20w50, “Penn Grade 1 Racing Oil” or “High Performance Oil,” confirm that it is GREEN in color instead of caramel. Not always easy to find, but lucky for me, the local Summit Racing store has it in stock.
These flat-tappet air cooled engines need oil with zinc and phosphorous. Most of the oils nowadays are missing these important ingredients. Years ago, Castrol 20w50 was the common stuff and was recommended by Porsche. But in recent years the oils have changed, and without warning. Look at the “API” rating. It is common to see “SM” now, and that’s BAD for these engines!
Another great oil is Royal Purple (again make sure it has the SJ api rating (Not SM!)). Some synthetics you need the off-road racing formula to get that. Also make sure it has zinc and phosphorous. Note, the phosphorous oil needs to be changed more often, every 3000 miles. Higher zinc (like 1500) is better than lower (1100). By the way, Royal Purple oil filter # 20-253 is correct for the 4.
Note this however: Jake Raby prefers Brad Penn over Royal Purple for the Type IV engines because of the flat tappets. So my conclusion is Royal Purple is great for the 6, Brad Penn is best for the 4. One thing for sure I do know is that the BP is absolutely as good as it gets for my 4, it is cheaper than RP, and it is readily available at my local Summit Racing store.