///the compression ration is higher than in an equivalent automotive engine. Use of lower octane ULP can lead to pre-ignition problems which can dramatically shorten engine life/// Peter and netters, Scott Cable and I had a discussion of auto engines a short time ago, and prevent a misinformation, auto engines typically will run compression ratios much higher than aircraft engines. Auto engines typical of today and in the past run ratios of 9:1, up to 10.5:1 compression ratio, using EGR valves, and knock sensors, and computer managed spark timing to control detonation. Since aircraft do not have these devices in most cases, they rely on ratios of 7:1, to 8:1 and 100LL to handle the job of preventing detonation. Also modern (post 1975) auto engines are all designed for use of unleaded gasoline, having come from the factory with hardened exhaust seats, and redesigned valve train components to eliminate the need for the lead lubrication of pre-1975 engines, and present aircraft piston engines. Auto engines also tend to have much closer engine tolerances than their aircraft counterparts due to better heat control, so there is less expansion internally. If an auto engine is set up as it was in the vehicle it came from, and the temperatures are controlled properly, it should be able to run any octane desired by the owner. I personally think the quality of the fuel is much better in the premiums, so I would only run that in my aircraft, but the engine is designed to run them all except for a handful of performance engines which the vehicle owner's manuals will make that obvious in the recommended fuel use section. This being said if one raises the compression, and advances timing, and allows the engine to run at hotter temps than higher octane fuel is going to be required to resist detonation, or some form of spark retard, detonation prevention, such as using the factory egr valve will have to be employed.
Colin & Bev Rainey KR2(td) N96TA Sanford, FL [email protected] http://kr-builder.org/Colin/index.html
