I recently replaced my factory mid-pipe & catalytic converters with an SLP X-Pipe with high flow cats. Went to the 1/4 mile dragstrip yesterday to try it out and had a decent improvement to show for it. My last trip to the track was nearly identical weather (upper 50's, similar barometer, overcast, etc.). Solid traction with no spin then or now. No other changes to the car other than the SLP Catted X-Pipe.

Before SLP X-Pipe: 12.34 @ 111.93 mph.
With SLP X-Pipe: 12.14 @ 113.05 mph.

Two tenths and 1.1 mph improvement. According to my math, that's about a 10 rwhp improvement.

 

How does it sound now? How much was the catted x?

 

Sounds raspier and a bit louder. Almost reminds me of a 6.4L PowerStroke Diesel from a 2008 or newer Super Duty pickup at wide open throttle. Kinda cool, but not what I had envisioned before I bought it. However, the performance gain was better than expected, so I'm very pleased.

I paid $360 for the cats/x-pipe and another $50 for the O2 extensions. And, I'm lazy so I paid our shop $160 to install it for me. The labor was a little more than I expected because they ended up having to remove my front BMR driveshaft loop, notch it to clear the x-pipe, then reinstall.