Best Oil for Flat Tappet Cam
As a hot rodder, race car builder, or classic car owner, the oil you put into your engine should not be a decision made lightly. Over the past 15 years, the oil composition of typical over-the-counter parts store oil has changed drastically. If you aren’t using the correct formulation, you can expect an almost certain death for one of the costliest parts of your vehicle. In our introduction to ZDDP, we shared some of the reasons oil has changed over the years and the benefits of zinc. With this installment of the ZDDP article series, we want to share the importance of selecting oil for the specific needs of engines with flat tappet camshafts.
Flat Tappet Cam vs. Roller Cam Differences
By now, as an automotive enthusiast, you are probably fully aware of the differences between a roller cam and a flat tappet cam, whether they are used with hydraulic flat tappet lifters or solid lifters. In case you aren’t, the examples shown below should paint a pretty clear picture.
Flat tappet lifters like these Howards Cams lifters have a flat bottom. But, to be technical, the bottom is actually slightly domed. The face of the lifter slides directly over the camshaft lobe.
Roller lifters like this GM LS7 Roller Lifter have a wheel supported by an axle and needle bearings at the bottom of the lifter. This design allows the wheel to roll over the camshaft lobes instead of sliding across the surface like a flat tappet lifter. Roller lifters are always locked in a fixed position rotationally, unlike flat tappet lifters, which must rotate in the lifter bore, or a failure will result.
As you can tell, a flat tappet lifter will have a much higher level of friction compared to a roller lifter. When a flat tappet lifter is sliding across a camshaft lobe, the thin yet super critical film of oil is all that is keeping metal-on-metal contact from happening. There are thousands of pounds of pressure per square inch on the small surface between the cam lobe and the lifter face. The oil additive ZDDP chemically reacts to these high load and high heat conditions by creating a hard phosphate glass layer, significantly minimizing wear on flat tappet cam lobes and lifters. However, not all motor oils have the necessary amount of ZDDP for flat tappet cams to keep them protected.
New engine technology has fully embraced the superior performance and wear qualities of using roller camshafts. Roller lifters provide such a high friction reduction between the cam and lifters that high levels of ZDDP additives are no longer necessary. The reduction of friction paired with the increasing emissions requirements have led to mandates that zinc levels in oil be reduced for mainstream motor oil.
Diagnosing a Flat Cam Lobe
So what happens if you don’t use oil with high levels of ZDDP in engines with flat tappet cams? Disaster.
It all starts with a little miss fire. Then a little lifter tap. Maybe some popping out of the carb. Then once you find out that changing the timing or tuning the carb doesn’t help, pulling the valve covers off to see a rocker arm not move while turning the engine over leads to a heart-sinking feeling. The cam went flat. With a flat cam comes an engine full of highly abrasive metal debris. More than likely an entire engine rebuild will be needed. Without the correct amount of ZDDP to protect the area between the camshaft and lifter, the oil layer alone will fail to prevent metal-on-metal contact.
Best Oil for Flat Tappet Cam Engines
Whether you choose to use a ZDDP oil additive, or a dedicated zinc-enhanced oil, be sure the oil contains between 1,200 – 2,400 ppm of zinc at every oil change. Engine break-in oils & additives (specific for engine break-in) typically have higher ppm levels, but continuous use of more zinc than recommended isn’t a good idea. We always recommend talking to your engine builder – they can usually recommend a formulation that provides reliable performance based on their experience. Also, some camshaft manufacturers will require use of a certain oil or oil additive, in case you need to make a warranty claim, so be sure to follow their recommendations.
Our final piece of advice would be to call, email or chat the experts at Speedway Motors. Our business is run by enthusiasts who’ve been building, racing and rebuilding engines for 3 generations. We know what you need, and which oils perform best.