Does anyone know what modifications I could do to get louder turbo noises on my '01 S40 1.9 turbo? Possibly a cold air intake, wastegate, downpipe, or boost controller and would stuff like that help?

 

Downpipe will increase airflow out of the turbo but you'd still be feeding a stock exhaust. If you went to a cat-back exhaust system (including something home made with straight pipes) you'd increase the airflow and sound. Your car still only makes 160 HP so its not going to really be a rocket unless you do some other mods like upgrading the turbo to a T14 (found on some S60s) and adding an ECU tune. Do those plus a downpipe/exhaust and you'd be in the 200+ HP range - enough to walk with GTIs. Otherwise, I'd invest in the handling - bigger wheels (I have 16s from a 2003 on mine), springs (at some point yours will snap and need replacing) and a rear sway bar to start. Stock struts are Boge Sachs so they are pretty good but you can find Bilsteins and match with some HR Springs etc or even shop for coil overs.

 

Thank you for the information, the car was very cheap and I am not looking to put a ton of money into it so any mods I will be doing will be as cheap as I can get them. I don't think that I'll be doing any turbo modifications but I will look into the HR springs and it has new tires so I wouldn't want to replace the wheels yet, I think I will just plastidip them. Where would I be able to get an ECU tune because I haven't found any and are they expensive for this car?