Bf-109E-7/Z 's GM-1 not working?

[boogabooga]

I'm on stock 4.13.4 with all complex engine management options "on".

At 7000m in reasonably straight and level flight over water, it seems that engaging GM-1 has almost no effect on top speed.

I'm not a total noob, and I am watching true airspeed and altitude in "cockpit off" view. I go to 110% throttle and let the airspeed reach a max(ish) value while trimming to maintain level flight. Then I engage GM-1. Nothing. It says GM-1 on the HUD, but see no effect on speed at all.

I tried again on version 4.09. The boost in speed was quite noticeable when GM-1 was engaged (~30km/h but nothing like the "advertised" 80 km/hr). Problem seems to occur starting around version 4.10. Does anyone have any more info, or can prove me wrong?