actually, therookie, you are wrong in your thinking all forms of backpressure is bad. if this were true then pro drag racers would not have headers on their engines. back pressure IS needed. headers also "suck" the exhaust out of the engine due to the other cylinders flow. too little back pressure creates bad idleing and a loss of power, just unbolt your muffler from behind the cat and see. i recently added a summit racing glasspack to my X. i had too little back pressure because the exhaust came out under the car via turndown. well i had to weld on the 2.25 inch tubing to the back to gain some more pressure, now i have more power than before. very low back pressure is only for high output engines like drag racers, dont think a stock explorer needs very little back pressure. i would have kept the origianl setup with the glass pack on my X if i could run it above 5K rpm because it seemed the only power i got was above 4000RPM and last time i checked thats almost where my rev limiter kicked in.