Two dynos are shown below.
Blue line was with 2.5 headers and midpipes (with cats) and 3.2L muffler.
Red line was with 3.2 catless headers, catless midpipe, and 3.2 muffler.
Max HP increase was just less than 10 HP and 12 lb ft of TQ, but usable power throughout the range is much better, at times 20 lb ft of torque as well as HP.
Still a bit fat on the air/fuel.
