I have a 2012 ford focus sel. Im looking to increase horsepower but dont know where to start
The quickest is to put on a computer reprogram unit like a bully dog or similar, then there are cold air packs, exhaust mods, and then you can start getting expensive with Nitrious injection or turbocharging with engine modify's. Of course these things will need to be backed up with some suspension and braking mods and possibly some engine bracing, if you go that far the tranny will also need either modded or replaced with a beefed up version to stand the increased engine output. Remember horsepower costs money.
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