📋 Quick Facts
On naturally-aspirated cars, a cold air intake adds 3-12 wheel horsepower on most engines. On turbocharged engines paired with a tune, gains stretch to 15-30+ wheel hp. The "+40 hp!" boxes are marketing.
What dyno tests actually show
Published Mustang Dyno and Dynojet results from K&N, AEM, Injen, aFe, and independent shops show consistent numbers:
- Honda Civic Si (K20): +6 whp, +7 wtq (AEM short-ram, no tune)
- 5.7L Hemi Ram 1500: +9 whp, +11 wtq (aFe Momentum)
- 5.0L Mustang GT (Coyote): +12 whp, +9 wtq (Roush CAI)
- WRX FA20DIT (turbo): +18 whp, +22 wtq (COBB SF intake + Stage 1 tune)
- F-150 EcoBoost 3.5L: +24 whp, +33 wtq (S&B intake + 91 tune)
- BMW B58 (M340i/Supra): +28 whp, +30 wtq (Eventuri carbon + JB4)
The pattern: turbo engines see meaningful gains because the turbo benefits from reduced intake restriction. NA engines are airflow-limited mostly at the head, not the airbox, so gains are modest.
Why marketing numbers are higher
Manufacturers quote "crank" or "engine" horsepower, not wheel horsepower. Drivetrain loss is roughly 15% on a manual FWD car, 18-22% on an automatic RWD, 25% on a 4WD with transfer case. A claimed "+15 hp at the crank" is roughly +12 whp on FWD, +11 whp on RWD auto. Then add seasonal variability of 3-5 whp between cold and hot dyno days.
When the gains are real (and when they are not)
- Real gains: Turbo engines with a supporting tune. The intake reduces pre-turbo pressure drop.
- Modest gains: Stock NA engines with restrictive factory airboxes (older trucks, V8s).
- Near-zero gains: Modern NA cars with already-good factory airboxes (most Toyotas, Hondas after 2015).
- Potential losses: Hot-air intakes pulling engine bay air on a hot day can actually lose 2-3 whp vs. stock.
Is it worth the money?
At $25-80 per wheel horsepower, a CAI is one of the most expensive ways to make power if measured by HP/$. A tune is almost always a better dollar value. But intakes deliver an audible "induction noise" that many owners value independently of the power gain. Buy it for the sound and the easier filter service - and treat the HP as a bonus.