how can you upgrade bmw m3 convertible to have more horse power

visit dinan is or active autowerke is websites. they will tell you all you need to know. be prepared to shell out big bucks, because it is a different level than tuning a civic.

It is a waste of time and money to upgrade the performance of an M3 to a significant degree.
An M3 is already at the peak of its capacity. Altering it to boost power would have dire consequences for the engine (and the whole power train itself).
Not to mention the safety of a convertible.

you could change your chassis if it is getting old or get a suspension tune up