Ok so I give, after saying I'll never do anything ricer-like to my Jeep.... To many people I know have gotten better gas mileage out of a "cold-air" intake.
I guess I could have just paid the $200+ for K&N setup, but thats not quite my style. All said and done I have $15 in mine, but I got some freebies.
Here is what I used, with retail prices, had I needed to buy everything new:
3" Exhaust pipe, 18" section: $6
2.5" - 3" Adapter - $6
Reusable/Generic Air Filter - $20
3/8 Drive, 9 mm Deep well socket - $3
Total - $35
You want the air flow to be as smooth as possible into the throttle body, so you can't just cut the pipe at a 45 degree angle and weld it back together, this would be to disruptive. I thought about having an exhaust shop bend a piece, but the bend would make the pipe too tall. So I decide I'd cut the pipe and weld it back together. Even if you don't have a welder, you might be able to talk an exhaust shop into welding the pieces for you, most of the time they will do little stuff like this cheap if they aren't busy.
You need to cut the 3" exhaust pipe into 3 pieces, I just used a hacksaw for this.
Here are the measurements I used:
After you have the pieces cut, weld them together. After I had them welded together, I used water inside the pipe to see if I had any leaks. Any place water dripped out I marked with a marker, then re-welded and re-ground them. Repeat as necessary until you have no leaks. You don't have to grind the welds, I just did to make it look smoother.
On my YJ, the CCV system, and the evap canister hook into the intake tubing, one is a 1/2" hose, the other is 5/8" hose. This is where the 3/8 drive 9mm socket comes into play. One side measures 5/8", the other side measures 1/2". Cut the socket in half. Then I drilled two holes in my exhaust pipe, one on each side, then welded the socket pieces to the pipe.
This next step is critical, so pay attention! You must hit the intake tube up with some Kentucky Chrome. If the intake tube work isn't shiney its not going to attract cold air, and you aren't going to gain power..... Adding a sticker to the tube will also help too.....
I was forced to quite a little early today thanks to some rain, but here it is "installed". The zip-ties obvisously aren't permnanent, I'll work on a better mounting setup on another day, as well as a heat/splash shield
Ok so how she run? Well it definitely made a difference, leaving the neighborhood, I turned left and let it run in 1st gear about 2000 RPM, for a moment, then planted the pedal, and the Jeep lit the tires up and instantly set the rear end sideways (Ok the groud was a little wet), but it definitely seems to be more lively now. The air filter does make some extra noises and you do here it sucking air in from time to time. I'll be filling up my tank later and we'll see if I actually gain some gas mileage, which is the goal.