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Restricted cat-back?
A well known N54 tuner has told me that an aftermarket cat-back exhaust will help the 1M gain top end power.
According to him, both the 135i and 1M share a restricted section of cat-back compared to the 335i and 535i.
Typically, cat-back systems yield relatively minor power gains (though they often produce much nicer sounds).
Has anybody compared the cat-back sections of 135i/1M relative to the 335i/535i?
Thanks.
Neil
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