WE USTA HEAR AMERICA PINGING

“TO UNDERSTAND THIS (HISTORICAL) ABNORMALITY OF COMBUSTION,” I wrote (sans the parenthetical modifier) in R&T back in December 1979, “we’d be wise to begin by examining the combustion process as God and Nicolaus Otto intended it.” You know, the old “Suck/Squish/Pop/Pooey” of intake, compression, power, and exhaust strokes.

 What is Ping? The abnormality of ping, detonation, or its extreme form, combustion knock, I noted, is “the sound of self-igniting end-gas, stuff out in the boonies of the combustion chamber that ignites on its own ahead of the advancing flame front.” This ignition in the wrong place and time “sets engine components to resonate (thus, the pinging noise).”

“It’s accompanied by increased heat and power loss,” I noted. “In its most extreme form, severe combustion knock can lead to melted piston crowns and other attendant distresses. In its mildest form, barely detectable ping is only a minor annoyance.” 

Back then I cited GM President Pete Estes calling ping “the sound of optimal fuel economy,” but then remember the part about melted piston crowns. 

Lead and the Fuel Expert’s Tie. There’s an oft-told tale of the 1921 discovery of tetraethyl lead as an antiknock agent. In fact, I repeated it back in 1979: “Given a badly knocking engine, a Model T with its timing advanced, for instance, the fuel expert would sprinkle a bit of mysterious liquid on his tie, and then wave the tie back and forth over the carburetor intake. The knocking would disappear immediately—and, of course, the mysterious liquid was tetraethyl lead.’ ”

“I’d hate to be wearing that tie, though. Since from the very beginning, even before EPA, OSHA, and all the other alphabetical protectors of the common weal, it was recognized that lead was toxic as hell.” 

A Modern Observation. The U.S. eliminated lead in motor fuels in 1996 after a 26-year phaseout. However, it wasn’t until 2021 before the stuff was banned worldwide. Gad, let’s hope the tetraethyl lead people don’t get to Trump.

Knock and Gasoline Octane. “A fuel’s octane rating, stripped of all the advertising jargon we enjoyed during those glorious days of super high-test, measures its resistance to knock.” One of the hydrocarbons, iso-octane, is highly resistance to knock and it’s defined as 100 on the octane scale. At the other extreme, n-heptane is a real knocker and is assigned the value 0. 

A fuel’s octane is determined by its place in the iso-octane/n-heptane spectrum. Two experimental methods are cited: Research Octane Number, RON, and Motor Octane Number, MON. “As a general rule,” I noted, “RON is a better indicator of heavy-throttle low-speed knock resistance, while MON better tests part-throttle or high-speed operations.” 

Three Grades of Gasoline. “Pump Octane” is the average of RON and MON. With the 1970s beginning of lead removal and other environmental concerns, gasoline suppliers eventually added a Mid-grade 89-90 (Pump) Octane to its Regular 87 and Premium 91-94.

Back to 1979 Ping. “Are the Engines at Fault?,” I asked rhetorically. “It’s clear that lower compression ratios lessen an engine’s appetite for octane, but they reduce efficiency as well. So this tradeoff has to be considered very carefully. We’ve seen compression ratios stabilize around 8.0:1 or a bit higher, and it’s generally agreed they’ll stay in this range. Going lower with normally aspirated engines only trades away too much efficiency.”

See Wikipedia for today’s general 8:0- to 12:0- range, with several innovative variations.

Searching for MBT. “For a given set of steady-state speed, load, fuel-air mixture, etc, any particular engine has an ignition advance setting that gives maximum torque at these operating conditions. This point of minimum spark advance for best torque (known as MBT to engine folks) is also close to the point of incipient knock, however. So in a very real sense, an engine that’s timed optimally for performance is tiptoeing particularly near ping.” (By the way, don’t confuse MBT with methyl tertiary butyl ether (MTBE), another thing entirely.)

Enter the Knock Sensor. I noted, “Knock sensors, on several new cars, turbocharged and otherwise, are automakers’ responses to this, and we’re likely to see more as time goes on. These devices allow timing advances that approach MBT (and incipient knock) without production variations and normal wear turning the engine into a recognizable pinger.”

How prophetic: Today, all gasoline cars have knock sensors—thus, the “usta” in this article’s title. 

Celebrating the Wizardry of Saab’s APC. Within a year, in 1980 I discussed Saab’s Automatic Performance Control.

“First,” I described, “there’s a pressure sensor similar to an oil pressure sender unit linked with the intake manifold, on the pressurized side of the compressor. Second, there’s a knock sensor of piezoelectric crystal type on the cylinder head, nestled between the intake runners of cylinders 2 and 3. Last, a sensor in the distributor keeps track of engine rpm, because detonation is rpm-specific as well…. The electronic brain ponders these three signals and sends a control impulse to a solenoid valve that’s added to the wastegate circuitry.” 

All, Sorta Familiar to Me. With a funny story associated to it: During my days at SAE’s Automotive Engineering magazine, I had summarized an SAE technical paper about APC presented by Saab engineers.

Later at an auto show, an SAE colleague and I were examining an odd sparkplug-looking gizmo at the Saab display. We asked about it, and the Saab rep replied, “That’s the knock sensor of our APC. You can learn about it over there.” And he pointed to my nearby SAE Automotive Engineering writeup. Opps; I had never seen actual hardware in preparing the piece. Fumbling at my lanyard name-tag, I smiled and thanked him. ds

© Dennis Simanaitis, SimanaitisSays.com, 2026