John@Fabspeed

Without the cats the CEL will be illuminated. There are a few owners here including the gentleman who posted the video above who has Fabspeed headers without cats and our valved side muffler bypass pipes.

He will verify my statement that there is no annoying drone or resonance. I would drive a GT3 with Fabspeed race headers and valved side muffler bypass pipes for 10hrs in one day and not be annoyed by the sound, and I mean that.

TRAKCAR

Cant get rid of the CEL?

snabbgt3

Yes, the new owner received my Fabspeed system plus the complete OEM exhaust system.

With the configuration I eventually selected (Fabspeed race headers without cats, side muffler bypass pipes with valves, and OEM rear center muffler) there was definitely NO low rpm drone that I felt excessive. For me, the OEM rear center muffler was necessary ... when I had the smaller Mini Maxflo mufflers installed I felt the drone too much. But as I mentioned before, in other thread, the drone is very much a personal preference and tolerance issue.

With the current configuration I drove back and forth to Watkins Glen for a DE event with PCA in early May (3.5 hours each way) and was satisfied with the absence of significant drone during the entire trip, highway as well as secondary roads. I drove the GT3 with valves open AND closed ... either was OK from drone standpoint.

The CEL light was always lit on my dash, because of the catless race headers. When we reinstalled the OEM system, at the recent sale of this car to a Calif. buyer, the CEL light no longer lit up as the OEM headers with cats were now present.

When using the race headers without cats in my GT3 the CEL was always lit ... perhaps future tune can correct this, when available. An ECU tune needs to be created to take advantage of the higher flow and lower resistance of these Fabspeed systems.