Shortround6
Major General
I think this is part of the problem. The Germans didn't seem to assign a new fuel code to the later fuel (if it was different) and they didn't dye it a different color. This does NOT mean they didn't actually improve it however. What are dates of the fuel tests? If the one with the high reading is late war it may show that late war fuel was of the higher rating. If it was one of the first then it may be a faulty test or show the Germans didn't really know what they had in that batch, performance wise. And lets face it, the British and the Americans didn't KNOW what they had , performance wise, in either of their own 100 octane fuels in 1940.
All fuel is NOT 30 points better in rich condition than lean. Most 87 octane fuel may show little improvement in knock rating in rich conditions. This is why there is/was a 91/96 rated American fuel. Gasoline that will show such an improvement from rich to lean needs to made of different base stocks than fuel that shows little improvement, or it needs different refining or additives. It is almost always more expensive and in some cases the base stocks/additives are in short supply and are better used in making the 100/130 fuel (or equivalent) than making 'super trainer fuel'.
A post war booklet by the Ethyl Corporation ( written in part by Sam Heron I believe) with Navaer-06-5-501 and USAF T.O. No. 06-5-4 has a page giving some of the specifications for MIL-F-5572 fuels of 80, 91/96, 100/130 and 115/145 grades. It also gives the same specs for ASTM D910-48T fuels of 80/87, 91/98, 100/130, 108/135 and 115/145 grades. Some of the gum residue tests and such are different but of some interest to us is the fact that some of the "middle" grades differ in the amount of lead per gallon allowed. The MIL spec allows 4.6ml of lead per gallon of 100/130 while the ASTM spec only allows 3.0ml per gallon for instance.