'The standard power plant was the DB 605A using B4 (87 octane) fuel. The engine's compression ratio was 1 : 7.3/7.5. Takeoff and emergency power of 1,475 H.P. was achieved with 1.42 ata of boost at 2,800 rpm. This output was initially banned by VT-Anw.Nr.2206 and was not reinstated until 8 June 1943 when Daimler-Benz issued a technical directive.' (Page 23)
A more careful inspection of the available primary and secondary sources reveal that 1.42 ata was in fact cleared several times through 1942 and 1943.
The clearance for the 1,42 ata, 2800 R.P.M. 'Start und Notleistung' rating was ultimately given for service use in October 1943 after several improvements to the DB 605A powerplant.
Technical Sheet issued by
the Quartermaster General
Berlin, 18th June 1942.
Subject: DB 605 engine in the Me 109 G.
A number of cases of breakdown in the DB 605 engine as
a result of pistons burning through occured. The following must be therefore observed.
The take-off and emergency output with a boost pressure of 1.42 atm. and 2800 revs. may not at present be used. The climbing and combat output with 1.3 atm. and 2600 revs. may, in the case of the older engines (for works numbers see below), be used when operationally essential.
via http://kurfurst.allaboutwarfare.com/If, in spite of these regulations, a piston does burn through, this is indicated by a strong regular vibration of the engine.
It is still possible to reach the nearest friendly base if the stress is immidiately reduced to about 1600 revs. and the lowest possible boost pressure. The vibration of the engine as a result of piston damage
remains unchanged when both magneto 1 and magneto 2 are switched on, so
that it is possible to confuse it with the a damaged sparking plug. On
the bench, bursts of blue vapour are emitted from the housing ventillator
when a piston is damaged.
In engines with reinforced pistons the danger of their
burning through is not so great as in the older version of the piston, but the take-off and emergency output may still not be used. The following engines are fitted with reinforced pistong headsÉ
Works numbers 25796, 35706 and 77731 and upwards. Also
the engines with the following works numbers:
76 900-77 250
The pistons of older engines (before above-mentioned works
numbers) will be replaced by reinforced pistons during the first partial overhaul.
Older engines mst be partially overhauled after 50 hours,
engines with reinforced pistons after 100 hours.
Partial overhauls of the DB 605 are at present carried out only by the industry (home or front-line repair works).
To prevent damage due to overheating of the ignition harness, the engines are at present being fitted with bakelite plugs and the engine cowlings with sparking plug ventilators. (Modifications to be carried out by troops in the case of aircraft already supplied).
Teleprinter message R.L.M. GL/C-TT No.1374/42 of 12.6.42 is hereby cancelled.