Up till recently I used the original Kendall GT1 (the green stuff). However, they don’t make it anymore. Luckily, Brad Penn has taken the original Kendall formula and updated it. The original GT1 additives and Pennsylvania grade base stocks are used in an updated semi-synthetic formulation. This oil has the advantages of both a synthetic and a non-synthetic at a competitive price. The very high lubricity/high pressure additives that have been taken out of API “street” oils are still in this product. The only reason to use a full synthetic would be for extended oil change intervals, not something you want for a race or hi-performance motor anyway.