In a recent test conducted by Speedway Motors, a detailed comparison was performed to evaluate the performance differences between stock exhaust manifolds and headers on a Small Block Chevy 604 Circle Track engine. This investigation aimed to provide insights into how much power gains could be achieved by switching to headers, a common modification among performance enthusiasts.
The Engine and Test Setup
The engine used in this test was a GM CT 604, a popular choice for Circle Track racing. This engine, equipped with fast-burn heads and a hydraulic roller cam, is a typical representative of both racing and street car crate engines. The factory claims it produces around 400 horsepower. To explore the impact of different exhaust setups, the team started with the stock manifolds before progressing to a tight-fit shorty header, and finally, a long tube header.
Stock Manifolds: The Baseline
The first test involved the stock exhaust manifolds, which are designed for simplicity and reliability. Upon testing, the engine produced 403.9 horsepower and 395.4 ft-lbs of torque, with the peak horsepower recorded at 5,900 RPM. However, the test revealed significant instability and erratic power delivery at the lower end, suggesting that the restrictive nature of the manifolds was limiting performance.
Shorty Headers: A Modest Improvement
Next, the team installed shorty headers, which are often used when space is tight under the hood. These headers feature unequal tube lengths and are not ideal for maximizing horsepower but offer a more free-flowing design compared to the stock manifolds. The results showed a slight improvement, with the engine producing 420 horsepower and 411.5 ft-lbs of torque. The headers smoothed out the power delivery and provided a noticeable increase in performance, especially at higher RPMs.
Long Tube Headers: Maximizing Power
Finally, the test moved on to long tube headers, which are designed to optimize exhaust scavenging and flow. These headers featured 1 3/4-inch primary tubes leading into a 3 1/2-inch collector, with the collector measuring approximately 12 inches in length. Long tube headers are known for their effectiveness in performance applications, and the results did not disappoint. The engine’s power output increased consistently across the RPM range, with significant gains in mid-range torque, which would be particularly noticeable in a street car.
Sound Comparison: Manifolds vs. Headers
Beyond power, one of the noticeable differences between manifolds and headers is the sound. The stock manifolds gave the engine a tame, almost factory-like exhaust note, reminiscent of an old Chevy pickup. In contrast, the headers provided a much more aggressive and resonant sound, which many enthusiasts prefer for their performance vehicles.
Maintenance Considerations
While headers offer clear performance benefits, they also come with maintenance challenges. Unlike the robust and trouble-free design of stock manifolds, headers are known for their tendency to loosen at the flange, leading to exhaust leaks. To mitigate this, it’s recommended to choose headers with a thicker flange and regularly check the flange bolts during routine maintenance.
Conclusion
This comprehensive test at Speedway Motors highlights the significant performance gains that can be achieved by upgrading from stock exhaust manifolds to headers on a Chevy 604 Circle Track engine. While the power increase is substantial, it’s essential to consider the trade-offs in terms of sound and maintenance. For those looking to extract every ounce of power from their engine, especially in performance or racing applications, long tube headers prove to be the superior choice.
