Conclusion
Our goal was to deliver a straightforward story that would provide readers with a rough idea about what the advantages of real-world header sizing are in terms of power. The odd dyno curves with the larger headers sent us scurrying for answers, and the ones we found pointed us toward internal engine tuning. While this test may have best benefited our Smeding 383ci combination, there is still much to be learned from it.
All of the long-tube designs made more upper-end torque and horsepower than the small-tube pieces, but they also lost power in the midrange relative to where their peak power was made. As for the smallest of the headers tested, we meant to provide a baseline number but instead netted the best overall power curve for a street/strip vehicle. We feel comfortable concluding that the shortest and smallest tube design held true to our initial theories by promoting as much upper-end horsepower as possible with a short tube while building an impressive amount of torque with a small diameter. The four collectors were all pretty much the same, and we didn't test them thoroughly enough to notice any operational differences.
The perfect parts combination is nearly impossible to bolt together the first time. Find an engine combination you like, use the recommendations in this story, and choose a header that's bigger and shorter for the races or smaller and longer for the street. After all, it's not the size of the header that counts--what matters is how you use it.
Parts List
Description; Mfr.; PN
1 ½-inch headers, '73 Camaro; Flowtech; 31108FIT
1 5/8-inch headers, '73 Camaro; Hooker; 2136-1
1 ¾-inch headers, '73 Camaro; Hooker; 2117-1
1 7/8-inch headers, '73 Camaro; Hooker; 2239-1
Stock SBC gaskets, 1.38x1.38-inch; Fel Pro; 1444
Hooker and Stahl adapter plate gaskets for large tube headers, 1.81x1.81-inch; Fel Pro; 1407
Vortec gaskets, 1.50x1.50-inch*; Fel Pro; 1404
LT1 and LT4 gaskets, 1.39x1.41-inch*; Fel Pro; 1470
383ci crate engine; Smeding; Call
* Parts not used for this application