Blenheim Mk IV start up ?

[Buzpilot]

Running from airstart, I have to keep rpm at bottom, to avoid engine failures.
And rpm gauges only show min 1600, but it's almost like engine control think it's 2xRPM, assuming it's really below 1400 rpm in cruise.

From a; Approval of Fairchild Bolingbroke Mk IV T, i read that rpm at takeoff should be at 2650 rpm, and thats impossible, even after a airstart.

Edit; I managed to run engines at 2650rpm, after i warmed up 15 minutes, but engines warmed up beyond 235C too fast, Cowl flaps maxed for air cooling didn't help at all.
So normal takeoff at 2650 rpm is impossible. And engines should be able to run 100% power at 2750rpm continously without overheating, so something is bugged here.

2.2 Engines
Model: Bristol Mercury XX air-cooled nine cylinder single stage Supercharged
radial rated at 820 hp for sea level take-off at 2,650 rpm and 4.25 lbs in2 boost
pressure. Each engine is fitted with dual Watford SP9-6 magnetos, a single
booster coil, a Claudel Hobson AVT.85MB carburettor incorporating
automatic boost and mixture controls and a Rotax E160 electric starter and
hand crank.

Source: http://www.caa.co.uk/aandocs/21124/21124020000.pdf