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1. 05:31 AM - Some interesting temperatures recorded (Lynn Matteson)
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| Subject: | Some interesting temperatures recorded |
Since I bought and installed the Rotec TBI-40 mechanical fuel
injector on my Jabiru 2200 mechanical lifter engine, serial #2062,
I've been pretty impressed with the results. Mainly the ability to
adjust the mixture. For the last month, I've been making flights at
various speeds and directions, and recording the EGT's and CHT's and
rpm's and fuel flows with the Bing carb, and for the last week with
the TBI. All the tests have been done with flights into the wind,
with the wind, and perpendicular to the wind, and mostly at about
2000-3000 feet AGL.
Yesterday I decided to average the results. While this is certainly
not a scientific approach, it's the best I could do without having a
recording device aboard, and feeding the info into a computer.
Bing: EGT spread 89 deg F.
CHT spread 44.4 deg F
Fuel flow 4.27 gph
Rotec TBI: EGT spread 84 deg F.
CHT spread 21 deg F.
Fuel flow 3.25 gph
While these numbers may not mean much without the actual temperature
numbers, it is interesting that I saw CHT's for the TBI as close as 3
degrees apart, ranging from 322 to 325.
(Keep in mind that I take my readings from a thermocouple attached
directly on the head, between the spark plugs, not on the spark plug
location which puts the reading about a half-inch ABOVE the head, so
my CHT readings will show a higher number.)
Other readings of CHT's show spreads of 6, 7, 9, 10, 11, 12, 20, etc.
The closest I was ever able to get the Bing CHT's was 30, 31, 34, 35,
36, etc. In thinking about why this differential in CHT's should be,
between the Bing and the TBI, I can only point to the fact that the
Bing has a horizontal throttle plate and shaft to which it is
mounted, and the TBI has....in my installation, anyway....a vertical
fuel-discharge tube, the only obstruction in the airflow at wide-open-
throttle (WOT). Now the Jabiru has a vertical splitter, and maybe
the vertical discharge tube and the vertical splitter make for less
turbulence, and therefore more even fuel charges going into each
cylinder, I don't know for sure. But the numbers are showing
something to be quite different in the CHT department at least, and a
less dramatic comparison in the EGT's.
I'm gonna start going on longer flights today, and see how the
numbers look while actually going somewhere besides around the patch.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 727.5 hrs
Sensenich 62"x46" Wood prop
Electroair direct-fire ignition system
Rotec TBI-40 injection
Status: TBI installation done...tests flights underway
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