8
Now, let’s calculate the proper engine box length for your setup.
Cowl length (minus) engine length = engine box length
If you measure the sides of your engine box, you will see that they are different
lengths. This is because some right thrust is built in. Add the 2 measurements and
divide by 2 to get the length at the center.
EXAMPLE: one side measures 6 5/8”(starboard) and the other 6 7/8”(port). Our
average uncut engine box length would be (6 5/8” + 6 7/8”) / 2 = 6 3/4” If we use
the example above and wanted our final engine box length to be 6 1/16”, then 6
3/4”(avg. original length) – 6 1/16”(final length) = 11/16”. I would have to cut
11/16” from each of the engine box sides. By cutting both sides the same amount,
we do not change our thrust angle.
Now, let’s mark and prepare our firewall for engine mounting before we glue it in
place.
First, remove your carburetor and trace your engine mounting plate.
EXAMPLE:
CL = 11 3/4” EL = 5 15/16” so,
11.75
- 5.94
engine box =
5.81
now let’s add ¼” so our prop will
_ .25
have a little clearance from the cowl
6.06
We would cut our engine box to be 6 1/16” long
After you trace it, cut it out and
then draw diagonals from hole
to hole. When you are done, it
should look similar to this:
