Re: 2005+ and Pre 2005 Focus motors.
Getting a vehicly dyno'd is exactly that. A shop that has the proper equipment will charge generally a flat fee to put the car on the dyno and you'll get a printout of the performance numbers. To get it tuned, a shop will generally charge hourly as they figure out the best air-fuel ratio while calibrating all your mods into the vehicles computer to get the most performance out of what is installed. Depending on the complexity of the mods it can take 1-4hours to do a proper job and cost around $500...if not more. It's not cheap in most cases, but it's worth while to get all the mods working in unison with the engine.
You can tune for low end torque at the cost of some HP. You can't tune for better mileage, however a lot of people say after a proper tune, mileage will improve since you're maximizing the performance potential of the mods installed on the vehicle.
If your unsure what to add to your vehicle. I'd wait until parts start to need replacement such as regular maintenance items. When its time for a new air filter, get a performance cold air intake installed, when its time for an oil change, get full synthetic oil installed with a good filter which will free up drag on the engine and give you an extra horse or two. When the exhaust is shot, replace it with a free-er flowing one. If you're concerned about increased noise with an aftermarket exhaust don't be. There are a few on the market that hardly increase noise while giving better flow than stock. If you want to go a bit more extreme such as a performance cam, or even a supercharger/turbo setup then a proper tune with a dyno is a must. You will notice a benefit just from tuning a vehicle with synthetic oil, intake and an exhaust, but it won't totally justify the money to get it done. Generally adding an intake all you have to do is disconnect the battery for ten to fifteen minutes and then reconnect it so the computer can 'learn' the new intake air volume and adjust the air-fuel ratio accordingly and a tune isn't generally necessary.
You can purchase programs to install on a laptop to tune the vehicle yourself, but that isn't cheap. While on the 'cheap' subject, there are programmers available that will allow a mild tune by changing spark advance etc to aid in increasing vehicle performance. Some chips include but not limited to JET, Superchips & Hypertech which are the most popular. JET chips are the cheapest and don't give good gains, but are available for nearly every vehicle on the market. For smaller engines with minimal mods a custom tune at a shop is still the way to go. With today's modern electronically controlled engines, it's easier to customize mods to work in together on any particular vehicle.
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!