Hi Area 51
Graph 6 on page 7-10 is in fact airbox pressure, not manifold pressure. That
would
be the pressure before it gets to the carbs. The wastegate is in fact fully
closed at idle position and up to about up to 1/2" advanced. There is turbo
pressure even at idle and because the butterfly is mostly closed and whatever
pressure there is can't escape thus airbox pressure increases, it increases the
airbox pressure to 44" as per graph. When the engine is off and you move
throttle
to idle, the wastegate closes. Then you advance it to about 1/2" it opens.
Net increase of power over straight 912 doesn't start to occur till about half
throttle.
The old TCU had a airbox temperature intervention temperature of 160F, the newer
style TCU 190F. Even with new style TCU, if for whatever reason you are going
to trust that your 914 is going to be making boost HP and not 912 normally
aspirated
HP, and your life is going to depend on that, Rotax suggests a DO 178
B take off. See page 3-11 in Operators manual. In other words, move the
wastegate
to the closed position (which you can do by placing the throttle lever to
less than 1/2" advancement) then turnoff your TCU. Now you have a closed
wastegate.
One needs to be extremely careful doing this, you can easily exceed maximum
boost. That said, if you advance slowly and select maximum boost using the
throttle, you can limit boost pressure. Just like at idle where airbox pressure
is way up and manifold pressure is way down, doing a DO 178B take off airbox
pressure will be way up and you are limiting manifold pressure with throttle.
At high power settings this is not something you want to do for a very long
time as it's hard on the turbo. But to clear those 50 foot trees taking off
downwind from a short field (which you should probably not be doing in the first
place) but if you ever do that or something where you don't the turbo to
quit when you can't abort, best eliminate uncommanded removal of turbo boost.
Ron P.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511031#511031
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