Here are some exhaust muffler tests done by various people or magazines.
Some interesting reads.
http://www.gusmahon.org/html/mufflers.htm
http://www.pontiacstreetperformance.com/psp/exhaust.html
http://autospeed.com/cms/A_0383/article.html?popularArticle
Some charts;
I’ve enchanced the above chart to make it easier to read. Not sure if the RPM-numbers are correct above but that’s kinda moot IMO.
http://www.geocities.com/MotorCity/Pit/9975/dataBySubject/mufflers95.html
Click image for larger version
