What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

How many FIREWALL PASS THRU do i need

osaleh

Active Member
Hello

I am building my RV7A , my lycoming O-360 engine is on its way and so will the dynon VFR package. I was wondering how many FIREWALL PASS THRU points do i need and where is the best location to have them?

best regards.
 
I installed one on the right and one on the left and it has worked out great. I also installed extra unused wires thru them to make future installations easy. They have come in handy several times already! Good Luck!
 
Depends on the complexity of your avionics and where you have your EMS box. I thought I could get away with two 3/4" passthroughs, but found that wasn't quite enough so had to add a third one. That thermocouple wire is kind of thick, and one pair for each CHT and EGT adds up. If I had to do it over, I would have used two 1" passthroughs which would be enough.

Just for reference, here's my setup:

Right passthrough
-----
(18g) "Always-on" +12V
(3x22g) Oil pressure switch (for annunciator light)
(22g) Starter terminal engaged
(6g) Master power
(22g) Master contactor switch
(18g) Alternator field
(22g) Starter enable
(2x18g) Magneto switches

Left passthrough
-----
(3x22g) Fuel pressure
(3x22g) Manifold pressure
(3x22g) Oil pressure
(3x22g) Fuel flow
(2x22g) Oil temperature
(2x22g) Ammeter 1
(2x22g) Ammeter 2
(3x22g) Tachometer

Center passthrough
-----
(8xtypeK) CHT
(8xtypeK) EGT
 
Depends on the size you plan to use but I did two of them and they work great. I also tried to keep my sensor wires separate from most other things.
 
i made 3 and am using 2. sounds like 3 is a popular number. very easy to plug if you don't use and it will never be easier to drill the stainless steel firewall than now.
 
depends

The word "depends" appears several times in previous responses, for good reason.

With the newer kits there may (or may not) be less ambiguity but I'm sure it still depends a lot on factors specific to your particular build. For me it was hard to know for sure until I had the engine hung, and all of the instruments at least temporarily in the panel, and most of the harnesses at least partly done.

My point being, delay as long as possible then use stiff wire / string / etc. to simulate the routing of all items and sort out any unexpected interference etc. before committing to the holes and pass-thrus. And pay attention to where you'll need to get your hands in there past accessories, or to remove the oil filter, or to remove the magneto, etc. so you don't end up with a wire bundle in the way of something like that.

EDIT: I see I may be in disagreement with Bob who says "it will never be easier to drill the stainless steel firewall than it is right now". Which is absolutely correct, and if you can know with confidence where there could be interference from engine accessories beforehand (like, by suspending the engine in place temporarily) then his may well be the better approach.
 
Last edited:
Back
Top