I just watched The World at War battle of Britain episode (on Amazon prime if anyone is interested), and they mentioned this program of the United States sending over higher octane fuel for British Hurricanes and Spitfires. Did this actually provide a measurable advantage for the British pilots? for instance if I was to fill an old Honda up with super premium gas I know it wouldn't noticeably make the car faster. Also they eluded to this program being conducted with a high level of secrecy, how were oil tankers sent across the Atlantic with any level of increased secrecy? Thank you looking forward to any responses!
100 octane fuel did give a measurable performance increase, yes. It allowed higher supercharger boost pressure to be used for a short period of time; the Merlin III engine of the Spitfire and Hurricane had a maximum boost pressure of +6 psi with 87 octane fuel, this increased to +12 psi with 100 octane. There are a substantial number of sources in the "+12 lbs boost & 100 octane fuel" section at the bottom of the [Spitfire I Performance page] (http://www.spitfireperformance.com/spitfire-I.html); [this chart] (http://www.spitfireperformance.com/merlin3curve.jpg) shows the increase in engine power (up to around 10,000 feet), [a memo] (http://www.spitfireperformance.com/spit1-12lbs.jpg) gives the approximate increase in speed as 28/34 mph.
It sounds like the programme may have been slightly overstating the secrecy aspect; there was a [front page article] (https://www.flightglobal.com/pdfarchive/view/1940/1940%20-%200897.html) in Flight magazine in March 1940, before the Battle, entitled "Hundred Octane", outlining the benefits, with a photograph in the same issue captioned "Hundred-octane fuel surges along the triple arms of a Zwicky unit into the tanks of Spitfires".
Dr Gavin Bailey's [The Narrow Margin of Criticality: The Question of the Supply of 100-Octane Fuel in the Battle of Britain] (http://ehr.oxfordjournals.org/content/CXXIII/501/394) from The English Historical Review sounds like a thorough coverage of the subject, I must get hold of a copy.
