Are aviation gasoline octane numbers comparable?
Aviation gasolines were all highly leaded and graded using two numbers, with common grades being 80/87, 100/130, and 115/145 [70]. The first number is the Aviation rating ( aka Lean Mixture rating ), and the second number is the Supercharge rating ( aka Rich Mixture rating ). In the 1970s a new grade, 100LL ( low lead = 0.53mlTEL/L instead of 1.06mlTEL/L) was introduced to replace the 80/87 and 100/130. Soon after the introduction, there was a spate of plug fouling, and high cylinder head temperatures resulting in cracked cylinder heads [71]. The old 80/87 grade was reintroduced on a limited scale. The Aviation rating is determined using the automotive Motor Octane test procedure, and then corrected to an Aviation number using a table in the method – it’s usually only 1 – 2 Octane units different to the Motor value up to 100, but varies significant above that eg 110MON = 128AN. The second Avgas number is the Rich Mixture method Performance Number ( PN – they are not commonly called oct
