Originally Posted by kmax1980
yup, biggest gains on the m3 are found by deleting the cat and chipping to remap engine to freer flowing exhaust...
the bmw engineers had to pull a few tricks out of the bag to make this car meet California emissions standards (anyone notice how rough the car idles when cold? this is why...)
without knowing too much about the subject, I could safely say defeating some of these emissions controls (i.e Cat and o2 sensors) you would unlock some relatively significant gains (40-50hp) at the cost of making your car non-street legal .... then again, will cops really catch you on this?
Well, you are correct with your guess and Turner deletes the pre-cats and tunes for that. 40 wheel gain, very significant.
Anyway, the car will be legal still with one set of cats, as in passing emissions. Tampering with any cat is illegal I think, but I don't know the exact regulations on this and they can vary by state.
I am getting a custom exhaust with a custom tune next week, I'll have more info.