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      02-06-2013, 10:43 AM   #30
Cozy
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Drives: E82 135i
Join Date: Mar 2011
Location: Surrey, England

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Is the 335is N54?

If so I can't see why sticking N55 335i mids on would be an issue, they must follow the same path.

The N55 is a more fuel efficient engine with one large cat in the downpipe. The N54 is fairly polluting and as a consequence has four mid-sized cats to controll its emmissions.