questions on cutting circular hole in firewall

thinking of cutting fresh air hole in firewall.
is it best to cut from inside motor. what is on other side of firewall, im guessing the carpeting of interior.
can it be cut from interior of car into motor compartment.
how do you finish off the holes, wire mesh.
anyone with pics especially of inside of car most appreciated.

Suspect the VS is same mould as my CMC - if so, there are 2 "firewalls" one just behind the engine fan (according to CMC build manual there should be a good size 3/4 moon piece of fiberglass cut out for fresh air intake (see build manual in library). The other (guess you could call it) firewall is the back of the rear seat area --- don't think you want to cut an open hole there unless you like breathing exhaust fumes.

Bob: There is a void or open area between the interior and the engine bulkhead. DON'T cut from the interior side. Raise the left rear of the car and put on a jackstand, pull the left rear tire and look in there before you cut anything. You'll see the open area above the transaxle.

~WB

This pic is from a bug, but what do you guys think of the idea? I thought it might be good for a car driven in Texas heat...

those do absolutely nothing - aside look like they look (and cheap IMHO)

i don't think i have ever seen anyone put vents behind their louvered firewall to keep the engine bay air flowing. Not a bad idea, but make sure you have somewhere for the added air pressure ot leave from (like dragging a parachute behind your car).

you'd be better off making sure the engine bay is sealed really well and the rear hood has vents to let teh heat that rises escape. you want to make sure the rear fan sucks in *cold* air and not air from the engein compartment.

That louvered chrome stuff is purely for looks (if you like that look) - on the Beetle that is indeed the area right behind the rear seat. My guess is the insulation which is stock there reduces the noise inside the vehicle - this is then just a covering. This is probably cheap Taiwan chrome which after couple weeks will already be rusting. If you were driving long distances guess you could put a scoup under the car by the rear seat to direct aid up over the transmission to the engine cooling fan - but since pan is flat anyhow suspect it would do nothing except compromise road clearance. Be curious to see a 356 in a wind tunnel - I've seen wind tunnel test disprove the urban myth that leaving the tail gate down in a pickup gives you better gas mileage (NOT True).

http://kwc.org/mythbusters/2006/12/episode_64_more_myths_revisite.html

tailgate down - better miliage & fuel savings - BUSTED!
Actually tailgate up = beter fuel milage!
Who would have thunk it!

For some real world aerodynamic applications, go to the library and grab the March 2007 Hot Rod magazine. It covers the subject very well, from race car to street truck. Data came from a guy who runs a wind tunnel for NASCAR. He agrees, dropping the tailgate doesn't matter aerodynamically (but it sure helps when backing up your boat trailer). Article includes stuff that almost always works and stuff that really doesn't matter. Good read. i xeroxed the whole article - cheaper than a subscription!