I'm looking at ordering an air filter for a tight spot, and it looks like the safest bet to fit is a K&N, 3.5" wide, 4" long. Anybody think I'm going to be missing out with that small of a size and should try to squeeze the 5" long one in there? I'm looking at 2.5" ID, as I have piping in that size I can make work.

 

my new filter was 6 inches long and i trimmed the hood to make it fit. the 4 inch filter is very frigin small for my money but i plan on making alot of hp so to each there own.

 

According to the K&N website, a 1600 cc engine at 7000 rpm needs ~33 in^2 of effective filter area. Taking into account the seals at both ends, the 4" filter will provide ~35 in^2 of filter area, so it's just big enough. But I'm not sure that having a turbo won't increase the required surface area. Maybe I'll try the 5" and jam it in there.

 

I don't see how the turbo would not cause an increased flow above the stock 1.6L. You can figure it out if someone has fuel info, and AF ratio for both stock and a similar turbo setup.

 

Yeah, I went back and did some more quick calcs, and it looks like the 6" would get me to 11 psi, 5" to 6 psi, and the 4", well, maybe 1psi. So it looks like I'm going to have to cram a 6" in there.

 

dude it was a real tough fit for me i ended up cutting the flanges back on my 90 and my filter and still had to cut the hood, and use ductape as my 2 1/2 inch pipe had to be modded so it wasn't to long for me. If this doesn't work i am going to put a peice of pipe about as long as the afm in there and use the location i used with the afm alot more room there. GL man lemme know if you figure it out, it might help me as well.