The intake tube is 3". You might try to find one of those ricer type filters to fit. Mine has been working fine. It fits into the stock air box like it should and I just had to tighten the clamp down tight. Give it try, you might like it.LOL
Diameter is 6". I didn't notice much of a performace increase but right after I put it in the fuel milage went up about 1.5 mpg but that might be driving style. I live in a very rural setting and its hard to judge "city" driving.