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Subject: | EGT Temps / New economy kit |
--> JabiruEngine-List message posted by: <info@suncoastjabiru.com>
The following question (and my answer) was posted on *another* Jabiru
Engines list, and I thought it would be helpful to post here too. Let me
know if you have any questions..
Question:
Subject: EGT temps
What you guys running for EGT temps? Mine are between 1150 and
1250 F?
My answer:
EGTs are a relative measurement - it depends on the position of the sensors,
but (to answer your question) I run our 3300 Jabiru demonstrator to around
1420 in the cruise. This is provided by the latest 'economy' needle and jet
setup for the Bing Carb. The needle has a very different shape, and gives a
definite rich - condition at maximum throttle / load. The results from
Jabiru's (limited) testing shows the following:
1. Jabiru have said that the economy kit works well for 'standard'
engine loadings on their own (Jabiru) aircraft and propellers. They have
tried a couple of (very) experimental setups and it's obvious that the
engine loading has to be within a certain range for the setup to work. A
cruise RPM between 2700 and 2850 with a wide-open throttle rpm in level
flight of around 3250 should be fine, but an engine operating at (say) 2400
in cruise and 2700 flat-out would probably not benefit, and may in fact be
damaged by over-leaning.
2. The ideal fuel:air mixture ratio for the engine is 14.5 : 1.
Existing needle and jet setups provide around 12 - 12.5:1 which we all feel
is 'safe ground' when operating the engine in so many different
installations. The new needle /j et setup (as tested on Jabiru aircraft and
propellers) gives 14.3:1 which is pretty close, but still just on the
rich-side of peak. Hopefully you can see that a different propeller / engine
/ airframe combination will cause different loadings, and therefore
different results, depending on where the carburetor slide (and hence main
needle position) is.
With the above in mind, I'm confident to offer the carburetor conversion to
the economy setup for 2200 and 3300 engines with the following conditions:
a. Initially, we'll offer the conversion to aircraft which have EGT
measurement on all cylinders and also those which exhibit rpm/load
characteristics which conform to the information above. We need to know that
cruise EGTs are not exceeding 1450F and that wide-open EGTs are around 1350F
or less, and measuring the hottest-EGT (as per the EIS) will confirm this
easily.
b. Customers send-in their carburetor for conversion, and get the same
one back. The job involves careful re-drilling of an air-bleed jet as well
as changing-out some of the internals. I'll offer a turnaround within three
business days assuming parts in stock, and include a thorough inspection and
clean of the carburetor with adjustment to float levels (unless specifically
declined!), a check of the diaphragm, seals and gaskets, and replacement of
the float needle with the upgraded version (if applicable) with stiffer
spring. Cost is $185 which includes the economy kit and labor for converting
/ checking / adjusting. Additional parts (gaskets / diaphragms / float
needles, etc) charged extra, as is return shipping (Priority mail) and
insurance.
c. I'll need to discuss individual cases for low-time engines. Clearly,
we will have problems supporting a warranty claim if an engine has been
cooked after fitting the economy kit (unlikely if you follow the above
rules, but anything's possible). My advice is to get at least 80 - hours on
your engine before considering this. New engines are tighter and benefit
from running-in with a richer fuel/air condition.
Customers should note that they will need to re-adjust the idle setting on
re-fitting, but should see an improvement in gas consumption or more than
15%. Ours worked out to 22% improvement.
Could be just the thing to give your engine for Christmas, unless you're in
Florida, where you'll be wondering how you can do without the airplane for a
few days..
Apologies for the shameless commercial plug, but I'm thinking some will be
interested.
Andy
Suncoast Sportplanes, Inc.
2005-2 Mainsail Drive
Naples, FL 3114
Tel: (239) 394 6800 Fax: (239) 394 0726
www.suncoastjabiru.com
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