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05/09/2004 Those of us who have a Jabiru engine on their Avids know that the original
air filter box doesn't fit our engines the way it should. On my original installation, I used it unmodified
because to change the air filter I would have had to remove the engine, there was no way to access the airfilter
with the engine on. Also Jabiru recommends providing smooth airflow to the carburetor which is hard to
accomplish with hard bends required in a SCAT hose.
I looked at the local auto parts store for a filter small enough to fit between the firewall and the distributor
but I was unable to find one. Web to the rescue K&N Filters had
to have what I was looking for. Sure enough under their special application section they had what I was looking
for R-1260 - 3.5 in. by 5 in. cone filter. The filter is small enough to fit and provides more than
adequate air supply for 2200cc Jabiru engine. Also the flange inside diameter had to be just the right
size to go over the hose connecting it to the carburetor.
First things first - I've used automotive engine formula to determine filter size.
For my engine A=20.74 sq.in.
K&N filter I used is 3.5 in. at the base 2 in. at the top and 5 in. tall - that comes
out to the A=43.175 sq.in. - plenty big enough to do the job. The original Jabiru filter was about 40 sq.in.
I decided to use hot air butterfly which came with the original Jabiru airbox, and add fiter box onto it.
I don't like fiberglass smell, dust, or mess it makes so I've built my box out of .020 aluminum. I added
a removable lid which will allow me to inspect and replace the filter. Since I've never built anything
out of sheet metal, I struggled but the end result is acceptable. I know that some of you more particular
folks wouldn't be happy with it' but it will do for me.
Another part of the project was to improve airflow to the carburetor - SCAT hose is easy to use but
introduces too much turbulance to the airflow. Bing carburetor is very sensitive to turbulent airflow
in particular in the area of pressure ports. Automotive rubber hose - smooth on the inside - would
be a good solution if I could find one to fit over the carburetor throat. Auto Zone's M-206 fit that
bill perfectly.
As you can see in the attached pictures the whole thing fits - and I can replace the filter by removing
the airbox lid. I guess that's an improvement over what I had.
05/19/2004 I've email Jabiru Mfg in Australia a question to verify that my filter has been sized
properly here is the reply:
G’day Mark,
Your calculations for the filter size seem to be pretty well on the money. Originally we ran
2200’s with a smaller filter and never really had an issue with them. The larger airbox was mainly
designed to improve access to the filter rather than feed the engine more air. One of the more powerful
2200’s here in bundy is actually running one of the old-style small filters, so I doubt you’ll have
any trouble.
Regards,
Doug Smith
Engineer, Jabiru Aircraft.
There are some people who think that the sharp bend in the hose connecting to the carburetor will be a problem.
My original setup had the same sharp turn but used SCAT hose and my engine did fine. Replacing SCAT hose with a smooth radiator hose
I view as an improvement. Never the less I'll do some testing before maiden flight and report results here and to the Yahoo Group.
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