If they are the same size, then they are most likely 600 cells... The N54 had a total of 2400 (between the 4 Cats). Does the N55 only have 1800? I'm curious to know what the count is on the main Downpipe Cat. I know i've read that the main cat is larger than what is on the N54, so by that reasoning, It's gotta be a pretty high cell count. I'm probably going to swap my OEM cats back onto my 335 and put the HFC's on the X5 when I get it... It's funny though, that they went with a dual exhaust setup on the N55 considering that it's only one Catted Downpipe coming from the Turbo (split into two outlets) Maybe a Single Exhaust Setup would have been better... IDK
BMW X5 35i: Boopie Exhaust, Boopie Intercooler, K&N Drop in Filter...
Audi S5 2013 (Delivery Sept 2013): Mods pending review