Source by: http://www.cartuningguide.com/bmw-3-series-tuning.php
Tuning Tips & Advice
Available in standard form with power of up to 301bhp (depending on the year), so this goes to show the tuning potential of the 3-Series. From this you can increase the power from anywhere between 331.1bhp to 511.7bhp with mods ranging from a few subtle add ons to a full engine rebuild! And more in the case of most Turbo engines if you include an uprated turbo.
If you have a lower powered 3-Series your best bet for a mod would be an engine swap with the 301bhp 3-Series Saloon. BMW certainly know what they are doing when it comes to making a fun car and the more powerful 3-Seriess provide and excellent tuning base to work from. Your first engine modifications for your 3-Series should be an induction kit, sports exhaust and fuel boost valve.
* The modification that gives the biggest power gain on your car would be a fast road cam. Internal engine modifications that should be high up on your list would be polishing and porting the head.
The 3-Seriess come in various power levels right up to 301bhp as per the 3-Series Saloon If you apply a few tuning mods to this model of 3-Series you will see power gains from anywhere between 331.1bhp to 511.7bhp. Any more than this and you will start to see unreliability appearing.
Forced induction 3-Seriess respond exceptionally well to tuning mods especially remaps, also add an intercooler to your mod list. The top 3-Series offers a base power level of 301 bhp. In Turbo form the power gains can range from 391.3 bhp to 571.9 bhp! Many 3-Series owners improve the handling of their cars with slightly stiffer springs. A drop of 35mm will work well on most cars, any lower and you will hit other problems.
