For maximum horsepower, the coolest, most dense air possible should be available at the carburetor inlet. Keeping restriction in the inlet path to a minimum or better yet, pressurizing the air, is also desirable.

The denser the air, the more you can get into the cylinders. This allows the engine to burn more fuel and make more power. A hood scoop or outside air nozzle intake should be installed wherever rules allow. This is always recommended. Under hood air is heated by the engine and headers and reduces the amount of power that can be produced. A reduction in temperature of 10 degrees F. is approximately equal to a one percent power gain.

There should be a minimum of three inches of clearance between the top of the venturis and a hood scoop. If an air cleaner is installed, the tallest possible element is preferred with four-inch element preferred for racing engines over 500 HP.

When a hood scoop or external air intake is used, it is highly suggested that the carburetor be sealed to it. Otherwise, air will flow across the top of the curb and out of the inlet tract rather than into the air horn. If air is forced past the carburetor it can siphon fuel, causing the engine to run lean. Windshield DLLA138S1191 snorkels are especially notorious for siphoning unless the rear is sealed. Air pan kits for sealing the carburetor to the scoop are available or they can be fabricated. An air bell or radiused intake should be used whenever possible to increase air flow into the carburetor.

It is not unusual for a drag race car to improve ETs by 0.3 second and increase top speed by as much as seven miles an hour after installation of a sealed scoop. A car will not pick up ET after the scoop is sealed off if the scoop is too short or the fuel delivery valve system is inadequate.

On oval track cars, the same is true. Paying attention to the inle tract design will pay off. Depending upon track length, oval track cars will typically improve lap times by 0.1 to 0.5 second once an optimized air intake system is installed.