Is the lower firewall structural?

[bbrown]

Does anybody know for sure if the lower portion of the firewall is structural?  I would like to make a notch in the lower portion to accommodate the air intake like so:
http://bbrown.smugmug.com/photos/106918671-S.jpg
The engine I have is an IO360-C1C6, and it's intake faces the firewall, and there's not enough room for the throttle body without putting in a relief.

[GlennBob]

Dear Bbob,

I've not responded because I'm not a builder, but from what I can see, the main spar crosses the firewall above the area you show. I think as long as you stay away from the main spar and the longerons (area where the motor mounts attach),  I think you should be O.K.   Maybe a true EZ builder will respond.  Waiter would be a good one if you can get his attention.

Glennbob

[Waiter]

You should be OK, Be careful, there really isn't that much room in there. This is the area inside the "hell hole"

When cutting, don't cut into the center spar or the gear leg. (this will ruin your entire day)

Good luck

Waiter

[Bruce Hughes]

Many of us have a NACA duct in that area.   We also have an
access plate in the top of the duct so the inside of the "hell hole"
can be reached (with difficulty)

Just be aware that the area you are changing is extremely useful
for passage of (1) throttle, mixture, and carb heat controls  
(2) fuel line   (3) 12 V and ground wires    (4) sensor wires  
(5) rudder cables (6) aileron controls   (7) cabin heat air or oil line
and vacuum line if you have such

The area is nearly impossible to reach unless the aircraft is sitting
upside down.   ALL of the above (1-7) should be installed while you
have it upside down.   Nothing there is easy to change later

I think there is a VERY high potential for you to find that the change
in the plans was NOT a good idea.

It will be VERY difficult to change back to the original configuration
after you do the cutting.   I have a NACA duct there but I have often
wished that the air was coming in on each side ABOVE the strakes.
Lots of builders use downdraft cooling.  

 

Bruce Hughes