2000 Posts and climbing!!!
Join Date: Nov 2009
Re: High Octane on small engines?
Better late than never,I'll jump in.I'm an old Aircraft Mechanic and am quite familiar with AV-Gas.The LL100(low lead) is just the latest version of aircraft gasoline,the LL100 replaces the former 100/130 fuel,as well as 80/87,it meets the requirements of 100/130,with about half the lead content.There was also a 115/145 grade,and that still be bought in tank truck lots,and can be found at the Reno air races,and at some airports,but not many.The 100 number is the "lean" rating,the 130 number is the "rich" rating,actually the 100 is the MON,or "Motor Octane Rating". The 100LL and 100/130 and 115/145 fuels are made for supercharged engines,I know that 100LL will work fine at 48 in.hg(1.6 atmospheres,24PSI)for 5 minutes ,much above that,115/145 is required,and some of the military or racing engines,also use water injection too.The "slow burning" can be overcome with more spark advance,and richer mixture,and it will bring a return to "lead fouling" ,which some of you younger mechanics may have never seen.As to Ethanol,remember that when using a carburetor,10% Ethanol will lean the mixture 5%,and so on for any mixture of gas/Ethanol,100% Ethanol requires around twice the jet AREA.Pre-ignition and detonation,are both abnormal burning conditions,pre-ignition occurs before the spark plug fires,detonation occurs after the spark plug fires,pre-ignition can cause detonation,but detonation can't cause pre-ignition.