I did not want to experiment with oem options so I looked for other alternatives. I found those 3 web pages most interesting for ideas:
http://www.r3vlimited.com/board/showthread.php?t=185577
http://ls1tech.com/forums/16096461-post162.html
http://members.dodo.com.au/~wawawa/e30index.htm
Things I used: Offset tin snips, 2mm aluminium sheet, 2mm edge grip seal, a steel ruler, divider with two metal points and a pair of vice grips.
So here's what I have done, first I've printed this pattern taken from the 3rd link above, after editing it to the right size. (each square represent 1cmX1cm)
Then gathered my stuff
I traced the pattern on cardboard, adjusted that a few times then traced it to my aluminium sheet. I made two brackets incorporated to the box, both facing inward on the radiator side, one visible here at the top and the other one on the opposite lower corner. Both using existing holes.
With the lid:
I polished it using 1200, 2000, 3000 grit sand paper and Mother's mag and aluminum polish.
Before/after shot:
Inside painted black for maximum stealth... also drilled holes at equal spacing.
Its very easy to make and I'm well pleased with it. The car is now much more enjoyable to drive as the bassy reverberating resonance in the cabin is now totally gone! Man that induction noise was loud! The box is very solid too.
Top tip: Making a deep scratch using a carpet knife or similar, against a straight edge, will make bending the aluminium very easy at that spot.
Ok, have a nice day now
JF
Edit:
I could not keep the box clean and it looked bad with water marks etc so I had it powder coated black with a grainy texture. Looks better and easy to clean
I also put the plastic thingy back behind the headlights to avoid sucking water in!
