Join Date: Mar 2001
Location: Peoples Republic of Vermont
The "racing oil" designation allows the refiner to market the oil without having to limit the amount of zinc and phosphorus. If the oil is marketed as "ordinary" engine oil then it's subject to the government limiting these additives due to potential damage to exhaust catalysts on newer cars.
IMHO, step number one in selecting an engine oil is to choose the right VISCOSITY. The factors that dictate the correct choice are bearing clearances, ambient temperature range during use, and severity of use. Generally speaking, if stock bearing clearances are maintained then go by the manufacturer's recommendation for viscosity. In almost all cases, Ford recommended a viscosity for vintage Mustangs of 10W-30 for the majority of uses, 10W-40 if the ambient temperatures regularly exceeded 70 or 80* and a 5W-20 if the temperature regularly was below freezing. Consult the owners manual for your exact vehicle.
The next choice is whether to use a conventional or synthetic oil. In simple terms, a synthetic oil has the base stock chemically manipulated to desired properties, one of the main ones being to provide a molecular structure where all the molecules are the same size, which spreads out the load bearing properties over a greater range. This also results in lower friction between surfaces. Synthetics also withstand a higher engine oil temperature without breaking down. Conventional oils, today, are much better than what they were years ago and are suitable for use most of the time and are significantly less costly, which may be desirable if you change your oil frequently or if you don't put many miles on and change it only a couple times per year.
The last factor is quality. There are many different facets to judging oils from the content of the additive package to shear strength, viscosity index, etc. Google is your friend here.
Last but not least, the American Petroleum Institute classification system designates into what vehicles an oil is suitable for use. API classifications beginning with "S" are for gasoline engines and "C" for diesel engines. Some oils are "dual" class. It is advisable to NOT use an oil in an engine for which it wasn't formulated (eg. using a diesel oil in a gasoline engine) or using a "dual" class oil in an engine type not listed first (eg. using CF4/SL in a gasoline engine). The additive packages of these oils are specifically designed to work with the particular engine type, such as types and amounts of detergents, dispersants, anti-acid agents, etc.
Also, if you DO choose a synthetic oil, make sure it contains a minimum of 1000 ppm of zinc/phosphorous/ZDDP. I recommend this regardless of whether you have a flat tappet camshaft or not... flat tappets aren't the only engine components where surfaces slide against another... bearings, pistons/rings, etc., are still rubbing against another part. The anti-wear properties of zinc and phosphorous is exactly what they are put there for.
What, me worry?
- Alfred E. Neuman