• Dump your stock exhaust system and muffler for better power and economy.exhaust pipe image by A74.FR Ben Fontaine from Fotolia.com
  
  Introduced at the Paris Motor Show in 1998, the Focus was Ford's Hail Mary play for dominance in the popular sport compact and hot hatchback market. Over the course of its life, the Focus has had no fewer than eight different engines and five different transmissions. A few of these (most notably the 170 horsepower SVT engine) nearly qualify the Focus as a bona fide sports car, a status reflected by its vast aftermarket support.
  
  

Header

• If you're simply replacing your stock Focus' header for increased power, you'll face no shortage of aftermarket headers claiming to be the best. The larger 2.0L and 2.3L engines can make do with a good "shorty" block-hugging header, but you'll want to use a slightly longer and narrower tube unit for smaller 1.8L engines. Ford's 1.8L engines aren't exactly known for their bottom-end torque and throttle response; there's no sense making it worse for the maybe one to two horsepower gain you'll see with larger headers.
  
  

Converter

• While its factory exhaust manifold is already pretty good, the Focus' catalytic converter ("cat") isn't exactly the highest-flowing unit out there, so you might want to consider a high-flow replacement. Although high-flow cats may not be legal in some states, they're de rigueur for serious horsepower junkies with an eye toward future upgrades. Consider the cat the biggest cork in your exhaust system.
  
  

Exhaust Size

• One perk of having the cat attached directly to the engine is that you have the option of replacing the entire exhaust with a bolt-on aftermarket unit. While all the old-school guys will tell you that small exhaust pipes will help to increase torque, don't believe it. Past the cat, small exhaust pipes can only stand to inhibit exhaust flow and decrease horsepower. But don't go crazy: anything bigger than 2.5 inches is overkill for anything but turbocharged engines, and is likely to sound like garbage.
  
  

Tubing

• Exhaust drone is the result of high-frequency soundwaves vibrating the thinner portions of an exhaust system's metal tubing. As a rule, four cylinders like those used in the Focus make a lot of high-frequency racket, so resist the temptation to purchase those paper-thin, $2,000 titanium tubes you saw online. Thick, mild steel tubing will only add about 15 to 25 pounds to your car, and is certain to sound better. After all, it doesn't matter how fast your car is on the track if driving it gives you chronic migraines.
  
  

Resonator and Muffler

• When it comes to a muffler, forget about those straight-through cantaloupe-shooters that all the Honda kids are running. Like it or not, they sound terrible and are sure to result in mind-numbing exhaust drone. Consider installing a chambered (baffled) or hybrid-chambered muffler for the best sound. Here's a tip: talk to your local Mustang owner's club and see if you can acquire a used Mustang Cobra muffler. They go for cheap and sound pretty good on Focuses. As far as the resonator goes: get rid of it. You don't need it, and it really doesn't do much for controlling high-frequency sound.