I was thinking of using intercooler silicon pipe (3-4 inch?) in place of parts of my stock air intake. I want to feed some pipe directly into the airbox as the original piping is very narrow.

Is the silicon appropriate for the job? In particular, i'm worried if it rubs against the intake plenum it might melt and whether it fits under the bonnet without warping.

Your home made intake pics would be great...

many previous threads devoted to this mate

Yeah there is a s**t load of intake related threads on here. Unfortunately the search doesnt work to well yet.

Seeing as you have the standard EL intake setup first thing id do is change to an EF airbox, has a bigger outlet than the EL one. Leave the rubber elbow that comes off the throttlebody there, i know its a bit of a restriction but lots of people still use it in their intake setup nd still make good power. Then replace the plastic piping with 3" stainless and add the silicon joiners wheere necessary. Another option would be change over to a BA intake pipe witha 3" pipe to extend to the airbox.

FAST-XR i think it was made up a really nice looking intake on his EL xr6 out of stainless and silicon joiners.

Since most boosted cars use silicone in there intake pipes I'm sure it will suffice for your application. 4" would be overkill and probably too big to fit between the bonnet and manifold - 3" will do the job for you.

to do it completely from silicone you wil need 3 bends and a reducing bend
(2 bends if you get lucky and find a 4"to 3" 135 degree reducing bend joined to 80degree 3"from memory)
an apropriate amount of alluminium joiners,a very expensive stiff straight piece of 3"silicone 2 foot ?,cheap shinney hose calmps.
around $5-600 and an ebay headache should be enough to make your dream come true.

i reccomend for budget
include original piping to flex pipe then add
monza 3" alloy straight pipe from supercheap $35
3" blue silicone sleeve from super cheap $13
3" alloy pipe 4" long supercheap $13
massive k&n $85
ts50 aka tikford snorkel $38

Here's A godd thread that i posted a while back.
http://www.fordmods.com/ford-4l-and-6-cylinder-f1/show-us-your-air-intake-t70357.html

I want to retain the std air box but in some way modify the exit of the box.

The very narrow mouth is made from a rather complicated piece that is bolted to the airbox and the factory pipe attaches. One removed it is a nice 3 inch hole.

Id like to seal the new hosing to the airbox and do the 'supercheap' mod mentioned above.

Is sealing new silicon hose directly to the box doable???

is sealing it even needed ?
remove the old pipe and adaptor.
clamp 3 inch pipe to original flex elbow
clamp silcone sleeve to end of pipe
clamp small 3 inch pipe to sleeve
poke into lid add pod to pipe.
remove plastic in top of lid as required.
add extra speed holes,snorkels,cai as tasteful
the posibiltie and combos are endless

I want to keep my panel filter in place, no pod.