I'll toss out a snip from William Wynne's "broken crank" webpage since it deals with leaning the mixture and may be of interest not just to KR/Vair operators: ========================== When leaning, he would lean until he saw a decrease in airspeed, and then slightly enrichen it. The evidence at teardown showed that either this leaning technique or his Ellison EFS-3A installation was the cause of lean operation and evidence of detonation. In many installations, especially aircraft without mufflers or flown by pilots with headsets, detonation in the plane cannot be heard. It is important that pilots trained in flying Cessna 150s to lean the aircraft until the engine runs slightly rough and then enrichen it slightly, should not use this technique on a Corvair engine, especially below 8,000 feet. The difference is simple: a Continental or Lycoming with a compression ratio in the 7:1 range, when excessively leaned from cruise power settings, will experience a lean misfire in the cylinder. A lean misfire is a harmless event compared to detonation. Here, the air/fuel mixture has reached a point where it will not ignite. Conversely, leaning an engine with a 9:1 compression ratio like a Corvair has the potential to detonate the engine long before it lean misfires. This is aggravated by high available density, as in low altitudes or throttle openings yielding MAPs more than 24". Corvair engines can be leaned, it just requires an EGT and common sense. The contribution of detonation to crank failure will be the hardest factor to replicate, model or evaluate. But, successful builders will avoid detonation for a multitude of reasons, not just its potential contribution to crank failures. ==============================
Oscar Zuniga San Antonio, TX mailto: taildr...@hotmail.com website at http://www.flysquirrel.net
