SIXTY YEARS AGO, THE FASTEST airplanes on the planet were powered by enormous, complex V-12 piston engines made by Rolls-Royce, Allison, and Daimler-Benz. Sixty years later, some of the very same engines are still running, powering weekend warbirds, museum artifacts, and Reno racers. Only a few mechanics in the United States have the knowledge, skills, equipment, and temperament to keep them flying. These are some of them.
The Junkyard Cats
Follow a two-lane road running from Nowhere to Nevermind until you’re just east of Gilroy, California, and there, down an unmarked dirt road, is Dwight Thorn’s company: Mystery Aire Ltd. From this collection of ramshackle industrial sheds emerge the most powerful, reliable, and admired Merlin V-12 air-racing engines in the world. Engine blocks and parts are everywhere. Scarred junkyard cats sun themselves atop pallets of superchargers. Cylinder heads are stacked like cordwood. Every sump and valve cover is filled with eucalyptus leaves and spider nests. Crankcases are slowly sinking into the sandy soil—ashes to ashes, aluminum to aluminum.
How he works miracles in such a setting may be a mystery, but make no mistake: Dwight Thorn builds awesome engines that routinely win races. Looking a bit like Wilfred Brimley in bib overalls, the white-haired, 64-year-old Thorn is putting the finishing touches on a bright red Merlin with mirror-polished aluminum valve covers that will soon fill the snout of the two-seat TF-51 Crazy Horse, a Mustang that flies riders for a fee in Florida. Seventy-five percent of his work is overhauls of stock engines like this one. “But the two or three racing engines we do every year take just as long as all the others put together,” he says. Thorn charges $60,000 to $80,000 for an overhaul, depending on the condition of the run-out engine, and $160,000 to $180,000—and up—for a labor-intensive, 3,500-horsepower racing motor.
Exactly what do you do to hop up a Merlin? “Simple,” Thorn says with a grin. “Disconnect the boost [limiting] control. We’ve seen 150 inches of boost, which is where the gauge stops. And which is probably just as well.”
Most of us accustomed to more conventional motorsports assume that “tuning” separates the prime V-12 builders from the also-rans. Tuning means “porting and polishing” the intake manifold passageways to improve the flow of the air-fuel mixture, “boring and stroking” to increase the engine’s working volume, “bench-flowing and blueprinting” to ensure that the cylinders’ mechanical dimensions match—all that plus tinkering with spark timing and tuning exhaust pipes to boost evacuation of the combustion gases must be a large part of successful air-race engine building, right?
Nope. The category in which the V-12 engines run at Reno is called Unlimited, and the rules basically say the engines must reciprocate and turn propellers. There is no size limit, no rule against performance-enhancing devices such as turbochargers, superchargers, nitrous oxide injectors, designer fuel, exotic materials, or weight-saving techniques.
As a result, the top V-12 builders put their engines together using the strongest possible parts, reinforcing weak areas (such as the Merlin’s relatively vulnerable crankcase), and carefully assembling and torquing each and every nut and bolt, but with normal, stock profiles and settings for the camshafts, valves, and ignition.
And then they turn up the boost. The more air and fuel the supercharger can cram into the engine, the more horsepower it makes. But the higher the boost, the stronger the engine must be to withstand the unholy pressures inside the cylinder.
Thorn’s specialty is replacing Rolls-Royce rods with beefy, never-run Allison connecting rods and adapting them to fit Merlin crankshafts and pistons. This allows the engine to operate at 135 inches of supercharger pressure but at lower rpm because of the rods’ greater mass. Before Thorn’s imaginative fix, racing Merlins with their lighter connecting rods turned as much as 3,800 rpm, the propeller spinning so fast the blade tips were supersonic, which meant they weren’t creating thrust. Now racers can back the revs down to 3,300 or 3,400, allowing the prop to get a better bite but sending cylinder pressures into the stratosphere.
Most of Mystery Aire’s clients aren’t racers. “We’re dealing with a different kind of customer now,” Thorn says. “Back in the 1960s and ’70s, the majority of the owners worked on their airplanes, had military experience, some had even flown the P-51 in the service. Today it’s the nouveau riche. They’re like the Ferrari guys—people who’ve bought something they assume will appreciate in value.”