The low-temperature flow characteristics of a thinner oil help avoid significant wear at startup time and increase fuel economy. But single-weight "winter" base stocks don't perform well when hot, so chemists created multi-viscosity oils using high-temp viscosity index (VI) improver additives. Synthetics typically do not require large amounts of VI additives (in some cases none) to achieve excellent high-temp performance.
Synthetic Horsepower on the DynojetWe drove two test vehicles to Dynojet chassis dynamometers at Winter Performance and Strope Speed where the professional tuners and dyno jockeys could help us scientifically evaluate the effect of synthetic engine oil on performance. Test Vehicle No. 1 was a bone-stock 2001 Camaro SS 6-speed, loaned to GMHTP from the Chevrolet press fleet. The vehicle had enough miles that the oil had been changed more than once. Test Vehicle No. 2 was our very own "Project Thunderchicken," a vastly-hotrodded LT1 Firebird whose stroker 396 powerplant had made slightly over 400 rwhp on the Dynojet 40,000 hard miles ago.
In order to compare apples to apples, we first dyno-tested each vehicle with the used oil that was in the sump. In the case of Thunderchicken, the vehicle was due for an oil change, so after the initial test, we changed to fresh Quaker State 10W-30, a high-quality conventional mineral oil which meets the latest API SJ standards, and tested again. Finally, we changed the oil in both vehicles to Royal Purple 10W-30, a synthetic motor oil which meets API-SJ standards donated to GMHTP by the manufacturer for testing. RP synthetic lubricants are marketed through performance dealers for racing and hotrod usage and through other channels for industrial usage. In each case, we did our best to make sure that temperatures of the engine, oil, and inlet air were not a factor in comparing the two oils' performance. In each case, we made several dyno pulls, but not nearly enough to be statistically significant to a 95-percent confidence, particularly given the miniscule changes in torque and the potential for tiny changes to be cancelled out by "dyno noise." We chose the best dyno pulls with each type of oil and compared them.
From 4400 rpms to 5800, the Camaro SS was up on both torque and power using synthetic, with the dyno registering peak power of 325.4 rear wheel horsepower (rwhp) with Royal Purple synthetic versus 320.8 rwhp with the slightly-used unknown-brand mineral oil. It should be noted that in this test, we did not change over to fresh mineral based oil to quantify the effects of new mineral oil.
Thunderchicken has been a mite tired lately in the higher revs (we suspect the valve springs are weakening a bit). In the first Thunderchicken pull, peak rear-wheel power stood at 388.9. With fresh Quaker State 10W-30, power increased to 392.3. When we changed to Royal Purple 10W-30 synthetic, power maxed at 393.3 rwhp. Peak torque went from 382.6 to 384.5, to 383.9 with the RP synthetic. Average rear-wheel torque over the range of 2200-6000 rpm changed from 368.63 to 367.34, average power from 288.3 to 287.4.
In the Thunderchicken test, there was a 0.6 lb.-ft. torque change out of 384 lbs.-ft.--about 1/6 of a percent difference. A change of one horsepower out of 393 is about a 1/4th of a percent. In fact, applying T-test statistical analysis to the 76 pairs of results for torque and power across the range from 2200 to 6000 rpm for the two types of oil, we find a very small likelihood that the oil change actually made a difference in power. In the case of the stock SS Camaro, 4.6 rwhp out of 321 is about 1.5-percent (which might alternatively have been achieved by a change of fresh mineral-based oil). Still nothing much to write home about. Conclusion: It takes harsher conditions than a few eight-second dyno pulls for synthetic oil to really shine at our intended purpose: making the engine live a long time under harsh conditions without wearing out or catastrophic failure. In our view, any extra horses are purely a bonus.-J.H.
The Functions Of An Engine LubricantLubricants function to reduce friction, remove heat, and contain contaminants.