[NOS2Go4Me]

Here's the thing:

05-07 Duratec Foci came with secondary cat/resonator under the floorpan, before the primary muffler. When I did development work with MBRP (as a customer) before they disco'ed the Focus offerings, they told me that pipe was a cat. The main cat, as we known, is just south of the manifold on any Focus. I was always skeptical because I was told anecdotal evidence that while some thought Ford had carried the second (California) cat offering as stock for all Duratec Foci, it seemed too long/narrow to be an effective catalytic.

When we did development for the 2.25" and 2.5" exhaust offerings for the Duratec, I had them cut my cat/resonator off before my final fitting of the actual system. The final MBRP exhaust set was made to include said secondary cat/resonator out of legal concerns from advising customers to deliberately cut out their section of pipe that might have caused them legal issues otherwise.

When adapting a Zetec-era MBRP (or any other exhaust offering) exhaust, you shorten one of the pipes (normally the lead pipe to the cat) because the exhaust mani is at the rear of the engine, whereas on the Zetec/SPI the exhaust mani is at the front - hence the longer pipe.