K&N FilterK&N Filter, Pacesetter Header and Flowmaster Muffler:
My camera was toast at the time we did the installations, but I took some post installation pics once I got a new camera:
The K&N (model RE-0810 - note that this is a off-road racing model with only a 1 year unlimited mileage warranty) was the easiest part of the install. We took off the stock air box, put a 1" long piece of 3" steel pipe inside the end of the K&N outlet to reinforce it, put it directly into the stock air tube and used the stock clamp to hold it in place. I built a bracket to support the front with sheet metal, bolted it to one of the stock air box mounting points and used a sheet metal screw to hold it to the K&N. Then we drilled a 1/2" hole in the side of the outlet to insert the vacuum tube into (later I siliconed it in).
These pics of the header don't show much. Its the Pacesetter header for a 90 or older 4.0L XJ. The only modifications we had to do were to plug the EGR valve fitting (boxed area in the first pic) using a piece of 3/4" round stock and mig welding it in, trim the new gasket around the intake ports and to cut off the flange where it meets the cat converter as the 91 and after XJs don't have a flange. It was recommended to me to weld the Y-pipe to the header, but we couldn't figure out an easy way to do it after it was installed, and didn't figure we could guarantee the angles (or even get it in easily) if we did it before.
The Flowmaster muffler (model 42442) was a relatively routine install, the 2 1/4" outlet fro the cat fit directly into the 2 1/2" inlet to the muffler, we used a piece of 2 1/4" pipe inside the outlet of the muffler to the 2" tailpipe (that's gotta be replaced one of these days with a 2 1/2" one).
Net result: a bit more power, roughly the same mileage I was getting with the busted up exhaust we replaced (23-24 MPG - imperial gallons), and a REALLY nice sound.