| ___________________________________________ The issue was an annoying low frequency resonance in the exhaust note occurring between 1500 and 2200 rpm. This happened after removing both cats and installing SZ Super Split downpipes and larger diameter 2.5" stainless test pipes. I love the 100% free flow of the new setup... The quick spool-up, and the extra power; but the low frequency boom was very annoying. After 2500 rpm, the exhaust note smoothes out to a very sweet mellow tone; so I wanted to keep the overall system while tuning out the offending resonance. 
While researching my options, I read about “venturi reducers”. They are used to speed the exhaust gas flow and quiet the exhaust. In addition they have the effect of disrupting the amplitude of the wave oscillations within the tailpipe and muffler chamber. My benchracing [wishful thinking] theory postulates the faster sound waves will cancel each other inside the hollow muffler, instead of combining and resonating. 
I located a pair of 304 stainless venturi and tacked them into the tailpipes. It is recommended they be installed after the resonators and before the mufflers. I located these immediately downstream of the resonator/tailpipe flange. Four (4) tacks per pipe allows removal if I want to return to stock. 
The results were very satisfactory. The 'boom' is gone, replaced by a mellow exhaust note all the way through the rpm range. Because the venturi reduces the inside pipe diameter by about a 3/8 inch it is assumed there is some additional backpressure created. However, IMO by the time the cooled exhaust reaches this narrowest part of the pipe, it has already lost so much of its velocity that backpressure losses are nominal. I also think the increase in gas flow more than offsets any negative backpressure effects. Not withstanding back-to-back dyno runs, I could feel no noticeable power loss. Moreover, if there were a couple of horsepower difference, it would be a minor price to pay for a great new exhaust note. 
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What's the difference between Daytona and New York?? 
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Using Venturi to Cure Low Frequency Exhaust Booming - 
