This is directly from the Performance Fords Site:
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Unfortunately at the time of our prototyping, our project SVT already had a modified y-pipe before testing of our new equal length downpipe was conducted. The modified downpipe had exhibited gains on the bottom end (3-5HP and lb-ft of torque up to 5500rpm) when we first dyno'ed that configuration. The dyno chart shown here shows that our equal length downpipe had additional gains of 4-7 ft-lbs of torque and 2-4 HP along the rev range up to 6000rpm. While we were not able to compare our new equal length downpipe to a stock down pipe, performance gains have been clearly identified.
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