The Strong Silent Type
Continued from page 1
Exhaust and Tailpipes:
The ultimate exhaust system should be able to flow as much exhaust and let the engine run as well as an open set of headers does. Therefore, tests were conducted at the drag strip to compare the wagon’s performance with open headers to its performance with various exhaust and tailpipe combinations.
A mandrel bent 3.0 " diameter system with 3.0" Walker #17773 Dynomax mufflers and 3.0" tailpipes (available from Torque Technologies ) was tested against open headers and against a system consisting of the same 3.0" exhaust pipes and mufflers but using only 2.25" tail pipes. The temperature of the exhaust gasses at various locations was also measured to provide additional data.
The temperature measurements showed that exhaust gasses cool significantly before they reach the tail pipes. The larger diameter exhaust pipes and mufflers dissipate heat, causing the volume of the exhaust gasses to be reduced. This characteristic enables smaller diameter tailpipes and in some cases, even a muffler with a smaller inlet and outlet to be used. The benefit of this heat loss was apparent when we contrasted the back pressure values of the same muffler mounted in two different locations.
The charts showing the results of the performance tests are given in Figures 5-7. One chart also demonstrates the heat loss affects the back pressure measurements between the front mounted and rear mounted Walker #17749 mufflers.
From these tests, it was noted that the Torque Technologies system, with the 3.0" Walker mufflers, produces performance essentially equal to properly tuned open headers. It was also demonstrated, that the use of 2.25" tailpipes, caused only a small reduction in performance.
A crossover, which is an interconnection between both sides of a dual exhaust system somewhere in front of the mufflers, has been used by automotive manufacturers to reduce sound levels and increase performance. A crossover lets the constantly changing pressure in both pipes equalize by letting each half of a V-type engine simultaneously use both sides of the dual system. In other words, the crossover helps minimize the negative effects of back pressure. Most crossovers look like an "H"; however, another type of crossover has been recently introduced that looks like an "X".
A 3.0" diameter X type crossover (from Dr. Gas/Pro Motorsports) was fitted to the LeMans wagon. Due to their superior sound level reduction, the Walker #17749 Dynomax mufflers were used instead of the smaller case but larger diameter inlet and outlet #17773 units. Using the #17749 mufflers and Flowmaster’s 3.0" to 2.5" reducers, performance comparisons of the X type crossover and the original H type were made.