Let's be honest, your Mustang's factory exhaust manifolds just don't quite cut it, especially if your throwing together a serious build with a ton of high-powered Mustang performance parts. The stock manifolds of your 1999 to 2004 Mustang GT have small-diameter primary tubes and crimped tubing that restricts exhaust outflow and prevents your engine from making more power. You can get all the power back with a set of high-quality Mustang headers from Stage 3. If you're looking for decent power gains but don't want to ditch your factory mid-pipe, then shorty headers are probably for you.