alvis et al
The V16 was running a petrol/alcohol mix to avoid detonation at those high boost pressures. If you remember, one of the most powerful turbo-era F1 engines was the M12/13 BMW. Up to 1400 BHP in qualifying trim. These race engines ran on a mixture of 84% Toluene and 16% n-heptane. Why weren't they running on 100% Toluene you ask? Well, there were two reasons;
The regulatory body at the time didn't allow higher than a 102 Octane fuel
Toluene is very difficult to evaporate, so n-heptane was added to speed up evaporation for cold starting. Even so, hot air from the radiators was directed to the fuel tanks to aid in evaporation.
Here's a link to an Australian man who's been rebuilding just such an engine, there's even a dyno sheet:
http://www.gurneyflap.com/bmwturbof1engine.html
A photo from the archives of the engine running on a dyno:
And here's a link to the BRM V-16 running at full chat. Mohsin Sb. put it very rightly when he said it's the most beautiful-sounding engine in existence:
http://videos.streetfire.net/video/British-Racing-Motors-BRM_111609.htm
And here's a photo of the subsequent H-16:
