go to brenspeeds web site they have them under exhaust components u put the spacers in the put the o2 in the space this sets the o2 sensor further back from the exhaust gases in which will allow it to read cooler...this is posed to work with no cats...with no cats the exhaust is hotter which will send a different signal to the computer putting a spacer in will allow the o2 to stay cooler so the o2 sensor will still be in range of the factory signal....its mainly just a way to trick the computer jst like the mil eliminators but the eliminators us a resistor to change the signal...either way could work but it just depends on where the o2 bungs are in the exhaust if the bungs are further away you will still throw a CEL because the exhaust is cooler the further back you go...