Just overview My Opinions, Pros / Cons 912S vs 914
912S Pros:
* Less expensive
* Less complicated: no computer, wastegate, turbo, coking of oil
* Lighter
912S Cons:
* Thus far the exhaust systems I have seen for Europa 912S are far inferior to
the new style 914 exhaust. I do not like leaks and cracking very much in my
aircraft exhaust. Type 308 stainless the new 914 exhaust is made of allows
wrapping exhaust without damaging system
* 912S is not only higher compression, but larger displacement, upon start up
and shut down 912S shakes more, also kickbacks more prevalent, possible
causing Sprague damage even with HD starter. I.E. trying to start in the cold
and there is a bit of carb snot in carbs, using 100LL and battery is not
putting out what it does in the hot.
914 Pros:
* Turbo absorbs energy, thus a bit quieter
* High density altitude benefit
* Emergency War Power for up to 5 minutes
* Altitude compensation works better on Turbo / Bing 64s than with Normal
aspiration
* You can always run a 914 like a 912, but not vise versa, this will keep
temperatures down.
* 914 allows for easy modification of mixture by varying float bowl pressure.
I know many say this is not needed, but 914s tend to run a bit rich at
altitude and leaning is not a bad thing to do. I have 2 EGTs and a O2 sensor
with mixture monitor display on my 914 installation. Also have a switch to run
a bit richer if needed. Many will say who wants to run a 914 richer? Probably
anybody who has flown a 914 with dirty carbs and 1 side is running lean
because of it, or any number of places a intake leak occurred. If notice lean
mixture, reduce power, run rich land as soon as possible. Run lean, ignore and
over temp things at high power setting, you will probably get to where you are
going, costly bliss though.
914 Cons:
* Need to deal with hotter exhaust components so as not damage things.
* Need to understand how turbo works, and more important what to do if there
is a failure. If wastegate sticks closed the motor will over boost, besides
hurting the motor, you will probably run out of fuel where the fuel pressure
regulator can't keep up. Of course this is at 300 feet! reduce throttle and MP
RIGHT NOW. If you have other than a momentary switch for the
wastegate/computer, if left off chances are the wastegate is in the closed
position, this will cause over boost with full throttle.
* Lead can cause wastegate to stick, lubing with mouse milk or such is a good
idea whenever you can
* High temperatures in turbo can cause coking of oil. Synthetic oil best, but
need to deal with more frequent changes and lead deposits ( 25 hour changes
and clean oil tank screen) if using a lot of 100LL
* Need to deal with more complicated fuel system. You need to understand on
the 914 if you have less fuel pressure in the float bowl, than in the airbox,
you will run out of gas! Duh!! That said airbox pressure is measured in
absolute terms, in other words 34 inches at sea level is the same as 34 inches
at 18,000 feet. You want approx. 2 to 5 PSI over this. The problem is if you
are just measuring fuel pressure, that reading is over ambient pressure. Thus
7 PSI at sea level is less than 7 PSI at 18,000 feet. Best have a differential
gauge. With a excel spread sheet and MP and fuel pressure, could perhaps
squeak by, but you are not going to be able to follow trends. You can see that
you need more fuel PSI at altitude, if you have a slight clogged fuel filter,
or slight low fuel pump or restriction it can work fine down low and show up
high. Vapor lock more likely up high, best make sure you have adequate return
fuel flowing.
* Need to keep motor cool at altitude when you are making some BTUs where
there are not as many air molecules around for this purpose. Normal aspirated
just can't make many BTUs at altitude so this is not as much a problem. Also
not only less air molecules, but things boil at a lower temperature when there
is a lower outside pressure. Mogas will boil before avgas.
* Turbo will stop boosting if you get airbox air too hot. Turbo needs to
pressurize more at altitude.
I chose the 914. I will attempt to overcool. Installing a cooling air baffle,
and can heat up by closing cowl flap. Will drop and direct a good amount of
air to oil cooler, but install a Mocal 190 degree oil thermostat to get heat
up. Water radiator will get a good amount of airflow, and cowl flap can reduce
drag a bit and get temps up. Have Differential fuel pressure gauge, HD starter
and intercooler. Closed cowl flap and oil thermostat should help get temps up
on in-flight restarts after soaring.
Ron Parigoris
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