I am looking at getting a cone filter and replacing my stock air box.
What are the dimensions I need for a 91 dx? Also, is placing it behind the headlight an ideal spot? And what size tubing should I go for the intake to replace the stock plastic/rubber hose?

 

I recently installed a cone filter in my '94 dx.. it's well worth it in my opinion...

I installed it where the stock airbox is, behind the headlight..

It fits, a little bit of wiggling and it will go right in... You can get the cone filter and adapter off of Ebay for like $25-30 after shipping..

I used the stock rubber intake hose on mine for the moment, as far as I know, we have to make our own intake pipe, or modify off of another vehicle..

I've been told alot of stories on the size of intake pipe.. Some ppl like the 3" civic pipes, and some ppl say that you lose power with those.. Mine runs much better with just the cone filter at the moment.. If all you want is performance than just use the stock intake hose, if you want looks than you'll need to make one, get from another vehicle, or last time I checked on it, Gro harlem was making one for his 1st Gen... might want to check with him see if it ever got finished...

that's all the info I can offer.. Maybe do a search and you will find more..

 

I put in a rather small cone filter. I got it from K&N #RU-3580. It will work with the cone filter adapter from tradesonic.com. It is a round tapered universal air filter with a 3" mounting flange inside diameter, 6" base diameter, 4" filter top diameter, and a 5" filter length(not including the 1-3/4" flange length). There is not much more room for a longer one then the one that I got. It fits in there pretty snug.