CelticFan

True, but in order for it to detect a knock it's got to actually "knock" first correct? I'd rather it not knock at all to prevent any problems.

HiFlite999

iTrader: (2)

Okay, there's a lot of misinfo in this thread about aircraft and 100LL. First, even a short visit to your local airport would reveal 100LL selling for $5-$6/gallon - hardly a cost saving in spite of 'no road tax'. Second, while it's called Low-Lead, that's only because it is so compared to other earlier variations. One typically pulls the plugs every 25 hours or so to clean off the deposits, or worse, lead beads which can short out the electrode. Oil change intervals are similarly short - and btw, any modern car motor oil has minimal capability for dealing with lead contaminants.

Airplane engines are "like VW's"? Yeah, like BMW inline 6's are like Cummins inline 6's. A fair number of them will run legally on premium car gas, but those are generally in the "lower performance" category. Low piston speeds, high loads, and large bore (~5"!) all tend to demand more anti-knock properties than any normal car equivalent. From memory, the highest hp, car-gas rated, ac engine is the ~1952 vintage Continental O-470 of 230 hp and a compression ratio of 7:1. The slightly more modern Lycoming IO-360 has a cr of 8.5:1 and absolutely requires 100/100LL.

The most modern ac engines are trending back to lower octane requirements over worries that leaded gas will eventually be unavailable.