I have a downey header; when it was installed in my 4-runner it had straight 2 1/4" into a flow master and then 3" out, i really like the way it sounded, but I could have used a little more tail pipe, I only had 2ft. No cat.
It ran fine for awhile but after I had the truck for about two or three months it started running really rich, it would load up all the time and even with all the windows rolled up you eyes would water up and you get this really funny feeling, almost like you were high. I replaced the O2 sensor and it helped for like two days and then back to normal, I could not figure out what the rpoblem was.
You might start with the O2 sensor but you may need to investigate farther, I know that with the Downey header you have to purchase a universal o2 sensor and wire it in to the factory plug wire. I cant use a factory toyota O2 sensor, that may of been my issue.
