It's been a while, but we finally dragged out the Circle Track dyno mule for a new round of testing. This time around the idea came from a bench racing session where we were talking about different header designs and how they are "supposed" to affect an engine's performance. For example, unequal-length headers are popular in dirt classes where the tire size is limited (like IMCA Modified) because the common thinking is that while these headers do not produce the most power, they are less peaky and can help limit wheel spin. It's one of those things we've always assumed was true, but hadn't tested.

So with that idea, we called up Doug Schoenfeld at Schoenfeld Headers to develop a plan using Circle Track's dyno mule as a test bed. If you've been a racer for any length of time, you've probably already heard of Schoenfeld Headers. It is one of the most popular header manufacturers in the racing industry. Schoenfeld is known for producing a product that is consistent from one header to the next, is affordable for the average racer, and, most of all, makes good power. Choosing Schoenfeld Headers as a partner for this test was a no-brainer.

We also enlisted the help of the NASCAR Technical Institute (NTI) in Mooresville, N.C. NTI is a technical training school that combines general automotive educations with an advanced regimen specializing in stock car racing. In addition to fabrication, pit crew training and other racing-specific courses, NTI also offers its students an engine-building program stocked with two dyno cells (one engine dyno and one chassis dyno) and more NASCAR Sprint Cup engines than most single-car teams. NTI has provided the engine dyno facilities in all of our previous tests (oil pans and rocker arms). It not only provides expertise in getting good, reliable dyno results, but its teachers also have a wealth of general engine-building knowledge which is invaluable.

While Schoenfeld Headers provided the test components, Circle Track provided the engine and NTI provided the dyno facilities, it was the NTI students who provided almost all of the labor installing the engine on the dyno, switching out the headers and even logging the dyno pulls themselves (under instructor supervision). An added bonus to the story was that the students got to see firsthand how header selection can affect performance of a race-engine package. In all of our previous tests with NTI, we've been impressed with the knowledge of the instructors as well as the quality of the students and were eager to work with them again.

The Test We settled on three different header tests for our dyno session that covered some of the biggest design decisions most racers face: Stepped versus straight tubes, equal-length versus unequal-length primaries and four-into-one collectors versus Tri-Y collectors. By combining different headers with similar characteristics, we were able to eliminate several variables as well as use only four different sets of headers (instead of six) for the three tests. We did this by making one set of headers our baseline, Schoenfeld part number 1024LV. The baseline headers were a stepped tube design that expanded to 17/8-inch with a four-into-one collector and unequal-length pipes. All four headers were 18 gauge mild steel with identical flanges and all four started with 13/4-inch primaries.

The first test would compare a stepped-tube header to a straight-tube header design. The headers to be compared (part number 1024L) to the baseline have all the same features except the primaries are 13/4-inches all the way to the collector.

For the second test, we used Schoenfeld Headers' part number 1014LV to compare an unequal-length design (the baseline) to a set of headers with equal-length primaries. Again, all other variables were the same. Both stepped from 13/4 to 17/8 inches, and both used a four-into-one collector.