The entire idea of an aftermarket exhaust system, as well as headers, is to allow for improved evacuation of exhaust gasses from the vehicle. If these gases are allowed to linger in the combustion chamber, they will take up valuable space that could be better utilized by fresh air and fuel. This, in turn, depletes the potential power and torque of your motor (this is a bad thing). Heaters connect the primary tubes to a collector, which efficiently scavenges exhaust gasses and allows more complete evacuation of the cylinder during the exhaust stroke than is possible without headers.
How to Choose the Correct Headers
Choosing the Proper Header Tube Dimensions
To begin, you must respond to the following question: “What type of driving will you be conducting in the car?” When it comes to drag racing, circle track vehicles, and track day cars, greater power at higher RPMs is required; nevertheless, when it comes to street driving, a broad power curve with a low-end response is required for city driving from stoplight to stoplight. The RPM at which you will be operating your engine most of the time, as well as the throttle position (wide open throttle cruising vs 1/4 throttle cruising), will have a significant impact on the header tube size that is recommended for your application.
It is not necessary to go out and purchase a 1 7/8-inch primary tube header for your street-driven 350, which is often regarded as overkill. Not only that, but it can deplete the power of your engine. The majority of our technicians think that a 350 for street use will benefit from a header with primary tubes ranging from 1 1/2″ to 1 5/8″ in diameter and collectors ranging from 2 1/2 to 3 inches in diameter. What this size achieves is a speedier evacuation of spent gas while simultaneously developing just enough backpressure to provide a broad torque response.
For racing applications such as circle track cars, a 350 engine will typically be equipped with a primary tube size of 1 3/4 or 1 7/8 inches and a collector size of 3 inches or 3 1/2 inches, respectively. These engines often produce more horsepower and spin at a higher RPM than street-legal engines, necessitating the use of larger header tube diameters than street-legal engines. To achieve even higher horsepower and sustained RPM, such as that found in drag race engines, a 350 would typically be equipped with 1 7/8-inch or potentially 2-inch primary tubes and 3-1/2-inch or 4-inch collectors.