Having found a 1942 (?) copy of R A Beaumont Aeronautical Engineering: A Practical Guide for Everyone Connected with the Aero Industry (modern reprint http://www.pitstop.net.au/view/aviat...uery/plu/23199) it's interesting to read what he says about the "four degrees (types) of boost" used by British aero engines:

(1) Take-off Boost - ...an additional amount of induction-pipe pressure....accompanied by an extra richening of the mixture which prevents an unstable combustion termed detonation...(p. 105)

(2) The Rated Boost - often known as maximum climbing boost....boost pressure is reduced to a value which permits the engine to run continuously at that particular power output...(p. 105-106)

(3)Override Boost - For the greatest possible power output for take-off or emergency, an increase in pressure above the normal take-off boost is permitted on some engines. This condition is used in conjunction with a special fuel. (p. 106)

(4) Maximum Cruising Boost....

Thus it is specifically stated that override or emergency boost was used only in conjunction with a fuel that permitted the higher boost rating.

Acctualy the SIM should be: SUPERMARINE SPITFIRE: CLIFFS OF DOVER. :o I almost sure the right the devs must go to BoM. At least no spitfires there. Most of data here come only from two sources: spitfireperformance.com or from Kurfurst site. I am almost sure that the DEVS had other data, maybe from URSS evaluations of the SPITS and 109s that not exactly match the data presented here.

No Seadog, it was possible as we can see from the Operating Notes. I am sure that engine was trashed after overboosting to +16lbs but it was definately possible on 87 Octane fuel.

It definately was not good but it was possible. Pulling the tit and overboosting the engine is not proof of the use of 100 Octane fuel.

Thus the boost override could not be used in the unmodded condition since it would cause almost instant engine destruction, which is a very bad thing for pilots to do during combat...It was only after 100 octane was used that the boost override became a useful adjunct to increase low altitude performance.

Indeed. Though it was possible to use the cut-out without modification and without 100 octane, this was only allowed in case of failure of the boost control. It is clearly not allowed during combat situations. The Merlin engine manual is pretty clear about this and even put an emphasize on this restriction, as posted already:
http://forum.1cpublishing.eu/attachm...1&d=1337196053

read:
http://www.wwiiaircraftperformance.o...ne/rcw-pg6.jpg

The above story clearly pertains to an engine that was already modded for 12lb boost (and thus using 100 octane) and the match stick mod permit boost up to 18lb, and it has already been established that Hurricanes in France were using 100 octane fuel by May 1940.

Maximum boost with 87 octane was 7lb:

http://www.spitfireperformance.com/spit2pnfs3.jpg

Well a key point about the spitfireperformance website is it gives us data collected at the time in reports written at the time. It is unlikely that Russian test organisations would have got any nearer to the true performance figures than the companies building the aircraft and engines and their prime user the RAF and its test organisations.

Did the Russians ever get any Spitfire Mk1s and/or MkIIs? They did get Mk Vs and MkIXs.

IvanK supplied most, if not all, of the data for the DEVS.

Great posts Seadog.

Wrong - there are two engine tests, one on 87 Octane and one on 100 which both ran up to 10.5 lbs boost - there was no boost override used which, as Beaumont observed, required special fuel - ie: 100 Octane - to achieve. Later Merlin engines, such as the 45 series, were capable of boost override of +18 lbs but needed, and were designed to use, 100 Octane to do so. Later still +25 lbs boost could only be achieved using 150 Octane.

Where does it clearly say that?

It does not, the General Operating Notes clearly say he can use it.