Often overlooked in the pursuit of horsepower, air filters can significantly impact performance. On Engine Masters, the team tested 19 different air filter setups on a 489 cubic-inch big-block Chevy that produced 760 horsepower. The goal was to see just how much airflow restriction each design introduced and to rank them from worst to best.

While few enthusiasts run engines this powerful, the results scale down. A 760-horsepower big-block at full song pulls as much air as a 350-horsepower small-block at lower rpm. That means the airflow lessons here apply whether you’re running a mild small-block Chevy in a street car or a serious big-inch race engine.

The Big Losers

Some air cleaners strangled the engine. The worst was a 6.5×2.5-inch element that cost 145 horsepower, leaving it suitable only for low-output engines around 300 horsepower. A single-snorkel Mopar unit with one inlet taped off killed nearly 96 horsepower. Foam velocity stack filters and fly’s eyelids also dropped more than 70 horsepower each.

Even for a small-block, those setups would be restrictive. A healthy 350, with 400 horsepower, would quickly overrun them, proving that undersized elements are a poor choice no matter the application.

Middle Ground Results

More traditional round filters told a clearer story. A 10×1.25-inch unit dropped 33 horsepower, but 14×3 filters with paper or K&N elements only lost 10–12 horsepower. The test also confirmed that dropped-base housings flow worse than flat bases, an important detail for anyone trying to fit a carburetor under a stock hood.

K&N’s filtered lids showed mixed results. In some combinations, they hurt power, but when used correctly, they add airflow by directing air straight down the carburetor. That’s valuable knowledge for both small- and big-block Chevys, since carburetor efficiency is all about airflow direction and velocity.

The Winners

The top 10 results proved which setups really worked. A 14×3 Fram paper filter with a flat base came in 10th, losing 10 horsepower. A B&B housing with a K&N element followed at –8.9, and variations of 14×3 setups with solid or filtered lids filled out the middle ranks.

From there, the real winners emerged. A 4-inch K&N with a solid lid lost just 1.2 horsepower, essentially nothing. Running an open carburetor ranked fourth, while the K&N velocity stack matched it nearly identically at –0.9. Surprisingly, the improvised salad bowl gained 3 horsepower, showing the benefit of directing air straight down. The ultimate winner was an open velocity stack, which added 5.7 horsepower over baseline.

Lessons For Every Build

The takeaway is simple: the size and shape of your air filter matter. Flat bases, taller filters, and airflow directed straight into the carburetor deliver the best results. For small-block Chevy owners, that means avoiding undersized filters and restrictive stock housings, especially if the engine is built to rev. On big-blocks, the stakes are higher, but the principle remains the same: let the engine breathe.