Would this quiet down the PV noticebly? Or will it only help vehicles with no muffler at all?

http://www.secureperformanceorder.co...ProductID=2476




100% T-304 Stainless Steel Construction
Compact Size Fits All Racing Applications
Ultra Lightweight-Less Than 1/2 lb. each
Little or No Power Loss
Easy Bolt Installation
Insert Cones on 3", 3 1/2", 4", 4 1/2", 5"
Turn Down with Insert Cone in 3", 3 1/2", 4"

Let's face it! Open exhaust racing is a thing of the past. Sound requirements, mandatory mufflers, or maximum dB levels are found in all forms of racing today. From Mini-Stocks to Outlaw Sprint Cars, reducing the sound level is becoming the norm. Today's racers are spending thousands of dollars to go racing. The last thing they want to do is get put on the trailer for too much noise. The Vortex Insert Cone can help keep you on track.

How It Works: The Vortex Insert Cone, installed near the exit of the header collector or muffler outlet, provides a large friction area to reflect and dissipate sound energy, thus reducing the dB level. The open area of the cone is actually greater than the area of the collector or exhaust pipe, thus reducing a backpressure condition. Because no significant backpressure has been introduced, the engine is still able to use the scavenge ability of a good header to creat horsepower and torque. Dyno and track testing show significant noise reduction with little or no power loss.