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I have a very old article by Gérard Hartmann which stated that "Quand l'essence à 130 degrés d'octane est reçue par la Grande-Bretagne et la France en septembre 1939, des moteurs sont testés avec ce nouveau carburant. L'effet est magique sur le 14 N : la puissance s'élève aussitôt à plus de 1 300 ch au banc (niveau de la mer)." Thus I assume the upper part of the curve can be used with some sort of 100 octane fuel. The problem is that, as pointed out by Shortround6, there wasn't a well defined 100/130 octane fuel available before June 1940. Do you know the type of fuel used for your power curve? SR6 also asked whether such high power came at a cost in reliability.Here is the power curve for one of the latest type of Gnome-Rhine 14N, the 14N48/49 :
Can you tell us the secrets of the mysterious 14R of the MB-157? Alas, my French doesn't distinguish well between two speed and two stage superchargers....
If you want to know more about these engines, I AM the French Wikipédia notice writer...