Slick Talk - Oil Tech

Track days on road courses are becoming increasingly popular with the Pro Touring crowd. Even a couple of laps of wide-open throttle use will rocket oil temperatures far above 300 degrees F if the engine is not equipped with an oil cooler.

Thinner Is Better?

Besides the inherent high-pressure lubrication advantages in areas like the cam and lifter interface and piston rings to the cylinder wall that synthetics offer, there has been a move in the last few years to create lighter viscosity oils that can still deliver protection and temperature stability with thinner oils that are easier to pump. It's a generally accepted fact that thick oil tends to create higher oil pressures. The thicker or more viscous the fluid, the more power is required to push the lubricant throughout the engine.

The trick is to create an oil that requires less power to pump through the engine yet still delivers sufficient protection. Oil pressure is an indication of resistance to flow in the engine, so it makes sense that reducing the oil pressure (while maintaining sufficient flow to protect the internal components) will result in more power. Drag racers have been doing this for years with excellent results.

This is an oil cooler located in the nose of a Cobra replicar. The cooler is positioned directly in the path of fresh, cool air in an attempt to keep oil temperatures in line when running the car on a road course.

Farner showed us some Quaker State research that tested several different weights of synthetics to dig up some horsepower from this thin-oil theory. Quaker State actually tested five different multi-grade synthetics on a 300hp small-block Chevy, including a range of oils between 10W60 and an incredibly thin 0W10. While you might think that the thinnest oil would have the best shot at making the most power, the 0W20 turned out to be the best in terms of both peak power and best overall power. We're talking about minor power differences of around 8 hp between the 10W60 oil and the 0W20, which is still a great change based on how easy it was to make this power.

This test looked intriguing, so we decided to do our own testing with a much higher horsepower small-block. Our test "Mule" is Bill Mitchell's 454ci small-block Chevy that we spooled up on the dyno at Westech. For our test, we limited the testing to three different-weight oils starting with a petroleum-based 20W50, then to Quaker State's full synthetic 10W30, and finally to Quaker State's full synthetic 5W20.

Synthetics enjoy a significant advantage over petroleum-based oil in terms of high-pressure anti-wear characteristics such as the interface between the cam lobe and lifter. If you've ever handled synthetic oil, it even feels more slippery than conventional oil.

During the testing, we noted that the 20W50 oil temperature seemed to remain much more stable during the testing. As we tested the thinner oils, each less viscous oil seemed to gain oil temperature much more quickly than its thicker cousins. We also saw an accompanying slight drop in oil pressure as we tested the thinner oils, which we expected. Once we assembled all the data, it appeared that the thinner 5W20 oil performed much better, but after averaging the data, compared to the thicker 20W50, the average power was only marginally better. Average power is probably the better way to look at this data, since the one 10hp gain at 5,000 rpm is not consistent with the other tests. Plus, this would even out had we tested each combination over 10 runs and averaged the numbers.

The focus of this exercise is that thinner oil will support a slight power gain and the only real cost is around $10 or $15 per oil change. But besides the potential power gain, there are significant advantages to using synthetic oil, especially if you plan on running your engine hard at the next track day. The engine you save just might be your own!

Test 1: We baselined the engine with a petroleum-based 20W50 oil. All testing kept the oil temperature between 190 and 200 degrees F.

Test 2: We changed to Quake State 10W30, including the oil in the filter.

Test 3: Changed oil again, this time to Quaker State 5W20.