It seems like a lot longer, but about 12 years ago-circa 1996-the Great Leaning War was fought. If you don’t own a high-performance single, you may not have been a combatant and even if you do, you may have chosen wisely to remain on the sidelines.The short summary is this: George Braly, then and still a Bonanza owning lawyer and aeronautical engineer, wondered why the IO-520 wouldn’t run smoother when leaned. His investigations re-discovered what the late Continental engineer Carl Goulet had known for years: the log-and-runner induction system on these engines had some air flow oddities that complicated fuel/air distribution such that some cylinders ran richer (or leaner) than others. Braly’s idea was to micro tweak the fuel injection nozzles to balance the gas to the air and thus was born GAMIjectors, of which some 18,000 sets have been sold.As GAMIjectors took off, Braly further discovered-make that re-discovered-that engines ran at peak efficiency and were cooler and cleaner when flown on the lean side of peak EGT/TIT. Continental knew this, because they authorized lean of peak operation for the Piper Malibu in 1984. Any 10th grade physics student can grasp the science with a few minutes spent studying the EGT, CHT and cylinder pressure curves that have been out there since God created dirt, or at least relatively accurate temperature and pressure instruments.But a reasoned and calm understanding was not to be. Lycoming objected-and still objects-to lean-of-peak operation, claiming that it of itself is not harmful, but owners lack the instrumentation to do it correctly. Somehow the multi-probe engine monitor and, lately, MFD engine analytical pages the size of a small television, escaped them. Continental has run hot and cold on the idea, but most of the engines it sells for high-performance airplanes are factory blessed for lean of peak. None of Lycoming’s are, although some owners do it anyway. The airport couch-rat chattering class and no small number of mechanics blindly resisted LOP. You’d burn your valves. The engine would run too hot. Some kind of mysterious chemical reaction would erode the exhaust manifold. You’d void the warranty. Hair would grow on your palms. Never mind that there was no science or engineering to support any of this. Some mechanics who are absolute geniuses at bending metal and bringing spark and fuel together to create the magic of internal combustion are absolute idiots when it comes to understanding that combustion.Clearly, owners had to be educated in the hopes of bringing their mechanics along. Braly and two early acolytes of GAMIjectors-John Deakin and Walter Atkins–put together Advanced Pilots Seminars, a series of weekend courses designed to school discerning owners in the finer points of engine operation and leaning. And thus went forth across the land a new understanding of leaning based on actual science, not engine manufacturer reactionism or mechanic hideboundedness. After a few years, APS stopped the course because, as Walter Atkinson likes to say, “we won.” And given that every new Cirrus SR22 turbo exits the factory with a POH more or less requiring lean of peak operation, he’s not exaggerating. Yet still, a decade later, there are pockets of resistance.I periodically fly new airplanes for product review purposes and I’m occasionally surprised at how poorly some demo pilots have this leaning thing down. At Cirrus, they’re all over it-you’d expect that. Less so at Mooney and Cessna. I’m still occasionally told that “this lean of peak thing runs the engine too hot.” There was a time when I’d put my flight instructor hat on, draw the little CHTs and EGT curves and try to explain how it really works. I don’t do that anymore. As my boss says, we’re not running a school for boys.But APS is and they still occasionally offer the weekend course. George Braly emailed me this week to say the next one is scheduled June 20 to 22. Check APS’s site for the details. (www.advancedpilot.com)What’s curious about any resistance to lean-of-peak operation is that it exists in a world where avgas is $5 or more a gallon. If you could run your car the same way you run your airplane lean, you could increase fuel economy by about 20 percent. Who wouldn’t do that? Well, some people to whom high gas prices don’t matter aren’t interested in lean of peak and don’t want to suffer the slight speed penalty associated with it. Fair enough-at least the argument isn’t based on some phony claim about burned valves.Out of curiosity, I asked Braly how much total fuel savings GAMIjectors and lean of peak could conceivably be responsible for. “Current estimate is that there are about 18,000 GAMIjector kits and that at 125 hours/year, that amounts to about 2,250,000 hours annually.” Owners who run rich of peak may save about 1.5 GPH, while lean of peak on large displacement engines drops the fuel burn by 2.75 GPH. That’s a total of 6.2 million gallons a year or more than $30 million a year at current prices.That’s a big number. Moreover, for the individual owner flying a modest 125 hours a year, the payback on a $750 set of GAMIjectors used to be about a year and a half. Now it’s six months. Not bad for set of hardware you can hold in one hand.