You work hard to earn your paycheck. Imagine if only $0.10 of every $1.00 you earned made it to your wallet! You wouldn’t be happy, and you’d want to do something about it. That poor earning efficiency would be highly motivating to find a way to reduce that “tax” in order to improve your earning efficiency.
Now imagine that every gallon of gasoline is like that $1.00 you earned. According to a US Department of Energy study on engine efficiency, only 10% of the energy from your vehicle’s fuel ends up actually moving the vehicle. That’s a 90% “tax” rate, which is an incredible amount of energy loss across the engine, transmission, and the rest of the vehicle.
Looking at the chart, it is easy to see why turbochargers are becoming so popular! With 35% of the energy potential (in the form of heat) going out the exhaust, recapturing that energy and converting it to useful work just makes sense. Today’s Turbo V6 engines, like Ford’s EcoBoost, make more power with better fuel economy than big V8’sfrom 20 years ago – clearly demonstrating the performance potential of turbocharging.
What’s next on the chart, and what about non-turbo engines? Upon a closer look down the chart, friction stands out as the next largest “tax” on energy efficiency. Of the energy moving the pistons and creating horsepower, another 12% of that energy is lost to friction.
Accordingly, reducing friction in the engine is the next best way to increase efficiency (even with a turbocharger). With friction playing such a major role in engine efficiency (AKA fuel economy), it’s no wonder why motor oils have changed so much in the last 20 years. Modern, synthetic lubricants contain way more friction reducing additives than regular motor oil did 20 years ago.
However, an examination of the sources of engine friction reveals the piston ring and cylinder wall account for over 45% of engine friction. In light of that, reducing piston ring and cylinder wall friction is actually the number one area of increasing engine efficiency.
What’s the best way to reduce piston ring to cylinder wall friction? Thinner rings with friction reducing coatings provide the largest reduction in cylinder wall friction. Top engine builders in Formula 1, NASCAR, NHRA and other forms of professional motorsports utilize piston rings 1/3 of the size of piston rings found in production cars 30 years ago. Made from advanced materials such as 440B stainless steel or M2 tool steel and coated with friction reducing aerospace grade coatings, modern piston ring technology provides significant reductions in friction.
When combined with lower viscosity, synthetic motor oils, thinner piston rings greatly improve fuel economy, and that is why the major car manufacturers have all gone to thinner piston rings and lower viscosity motor oil – efficiency. For proof, just look at a 1990 Chevy Silverado compared to a 2020 Silverado. Back in the day, the 5.7 Liter V8 featured a 2.0 mm compression ring along with 10W-30 motor oil. Today’s Direct Injected 6.2 Liter V8 features a 1.2 mm compression ring that’s lubricated by 0W-20, and despite the extra cubic inches, today’s Silverado gets 30% better gas mileage than its older brother.
While motor oil can reduce friction, thinner piston rings offer a 2 for 1 – reduced friction and better sealing efficiency. What’s sealing efficiency? Piston rings provide the seal which keeps combustion gases and pressure above the piston and out of the crankcase. Consequently, another area of “wasted potential” is blow-by. Combustion gases that leak past the piston rings are not pushing on the piston, so that power is wasted. We call that blow-by, and better piston ring seal equals less blow-by.
Now you might be wondering how a smaller, thinner ring can seal better. Wouldn’t a larger ring work better? On the surface that seems to make sense. However, cylinder bores in engines are not perfectly round nor are they perfectly straight. A thinner piston ring is more conformable to the irregularities in the cylinder bore. Think about a thick piece of metal, it is nearly impossible to bend, but a thin piece of wire is easily bent. As such, a thinner piston ring conforms to the changes in cylinder bore geometry as the piston travels up and down the bore, and with less friction! Piston ring engineering aims to provide a ring strong enough to maintain proper tension and form yet flexible enough to conform to the irregularities of the cylinder bore. When that happens, engine efficiency improves!
So, when you’re looking for a “tax shelter” that will allow you to keep more of the power you worked hard to make with manifolds, heads, camshafts and fueling, don’t forget about the piston ring.