* The quality of the intake: A well-designed and properly installed intake will yield better results than a cheap, poorly designed one.
* Other modifications: If the car has other performance modifications (exhaust, tune, etc.), the gains from the cold air intake might be less noticeable or even negligible. Conversely, other modifications can amplify the benefits.
* Testing methodology: Dyno results can vary depending on the dyno itself and the conditions under which it's used.
It's important to be realistic. While you might see claims of higher gains, a 5-15 horsepower increase is a more reasonable expectation for a stock 1994 Mustang GT. Don't expect to magically gain 30+ horsepower from just a cold air intake.
