Its not much
slammed against a hardened steel seat 10 times a second swirled in a gale of white hot combustion gas. When an engine tanks prematurely or needs a midstream top overhaul, its often something to do with exhaust valves-bad guides, leaky seats, cracks around plug bosses originating near the exhaust valve.The engine makers and airframers have tried to meet these problems head on with mixed success. Cylinder cracking and valve issues continue to trouble owners, seemingly in cycles.
But with little fanfare and without even intending to, Cirrus Design may have just launched the boldest exhaust-valve rescue mission yet by all but mandating lean-of-peak operation for its new turbonormalized SR22. Its not the first time an airplane company has put lean of peak in the POH, but how Cirrus got there is one of the more interesting recent developments in GA-equal parts of good engineering, grass roots proselytizing and shrewd management.
Whats more interesting is this: Cirrus uses a variant of the IO-550 that both Mooney and Columbia have in their new turbocharged models, the Acclaim and the Columbia 400, respectively. Yet each airplanes POH calls for a different leaning strategy and the differences between the three arent subtle. What may be shaping up here is a laboratory of sorts shedding light on-if not proving-whether lean-of-peak operation has all the benefits its proponents claim for it. (Fuel savings are a given, in our view.)