I have just gotten a 2007 Volvo s40 2.4i and need help on what should I do to increase horsepower.

 

I'm serious when I say "trade it in on a T5 model". Net/net, that will give you the most reliable horsepower for the least money.

Other than that, the best thing to start with is a new air filter (not "system" - just a new, clean paper filter element), and plugs. That's likely to get you a few easy, cheap horsepower, and improve your MPG as well (more important now than it was a year ago!!!).

 

yep. its not easy to add HP to a NA engine. ECU tune, free flow exhaust/header may add 10 HP - not enough to really drop 0-60 times. Turbo engines on the other hand can gain 50HP just from the ECU tune and easily add 100+ when combined with downpipes/bigger turbos etc. For you car, I'd say forget the HP and go for handling/braking upgrades. For handling (in $ to benefit order) you can upgrade the wheels/tires, sway bars, shocks, springs, bushings. For brakes you can upgrade pads, rotors, calipers (more pots = more clamping force) and upgrade to larger rotors (larger rotor = more heat dissipation ), braided flex lines. Last option is leave the car stock and upgrade the stereo/speakers and enjoy your tunes while driving legal.

 

Well at the moment I live in RSA but on most cars the cheapest and safest way is to change to the higher output one , as mentioned in your case is to go for a T5 , not sure in your country but here in RSA the Turbo ones are quite cheap as people are scared of an old turbo car , but the T5 is a low pressure unit that is quite good , have not heard of many turbo problems , mine is still fine after 16 years .
You will then have an upgrage that is virtually impossible in your 2.4
Remember that once you have the T5 to get more power is quite easy and relatively cheap .We have one T5 standard for 17 years with 125 000 km on its a spare car now as in RSA one needs that as their is no good Publick transport
But remember more power less reliable as manufactures make the brakes , suspension ets to handle the power unt , more power better brakes , better suspension , stronger drive shafts etc

 

I've owned 3 turbo cars so far - and none have experienced issues related to being a turbo engine. #1 1995 850T - put 250K miles on it from new sold it when my daughter inherited a newer car. #2 2000 S40 with 140K miles. Son's daily driver. Runs like a charm but has had typical S40 repairs, most recently needed a PNP switch. 2012 VW CC 2.0T. My daily driver with 100K miles. Still runs like new. I put in IPD sway bars and bilsteins in the 850 and it drove better than an R. S40 is bone stock except for running 16 inch wheels but could use an upgraded radio head unit. CC is bone stock - given I now telecommute, it gets used about 500 miles a month so not much point to doing any upgrades, but I am tempted to get some nicer 18 inch wheels and use the originals with my winter tires.