New 3" exhaust with 2.5" Tailpipes

From my draft in 2002 or so. We even tested 2.25" tailpipes

Exhaust and Tailpipe Testing

For these tests, the performance of Torque Technologies’ mandrel-bent 3.0” pipes with an H-type crossover and 3.0” inlet and outlet Walker 17773 Dynomax mufflers feeding 3.0” tailpipes was compared to 1) open headers and 2) a system consisting of the same 3.0” pipes and mufflers but with 2.25” tail pipes. The goal was to see how much the size of the tailpipe affected a typical 455’s performance. Additional tests were made of the system’s backpressure and sound. Pressure taps were installed in four locations on the system and the backpressure (in inches of water) at wide-open throttle was measured. The sound levels were measured with the engine held at 2200 rpm and the sound level meter was mounted on a tripod 25 feet away from the outlet of the exhaust. The performance tests were run at Kansas City International Raceway and all weather and track conditions were monitored to insure consistency. Temperature measurements were taken at various locations on the system to determine the effect, if any, of running the smaller diameter tailpipes. Fast reacting temperature probes were positioned in the same locations used for pressure measurements and the exhaust gas temperatures were monitored.

Exhaust and Tailpipe Test Results

Surprisingly, the smaller tailpipes did not hurt performance as much as expected. The temperature measurements taken at various locations on the pipes offered one solution. The measurements indicated that the exhaust gas was cooling significantly before reaching the tailpipes. Heat energy is lost because the large diameter exhaust pipes and mufflers (having a lot of exposed surface area) dissipate it. This heat loss causes the volume of the gas to be reduced enabling smaller diameter tailpipes and, in some cases, a smaller muffler to be used without increasing backpressure. [Insert figure. Figure 12 shows the results of temperature testing.]

To verify that the heat loss and its related volume reduction really lower backpressure, another test was performed. The Walker 17749 Dynomax mufflers were used and moved between a front and rear location. The backpressure at the collector was measured and recorded. [Insert figure. Figure 13 demonstrates how the backpressure dropped when the muffler was moved from the collector to the “traditional” location in front of the rear axle.]

[Insert figure. Figure 14 shows the results of the drag strip performance tests.] From these tests, note that the 3.0” diameter Torque Technologies system with the 3.0” Walker 17773 Dynomax mufflers produced performance essentially equal to properly tuned, open headers. The other tests demonstrate that the use of 2.25” diameter tailpipes causes only a small reduction in performance on this particular combination due to the large amount of heat dissipated from the exhaust gas before it reaches the tailpipes.