Hi Chessie 4905 - As you said: Nelson Global Exhaust products has a section in their aftermarket catalog that details muffer specs for both gas and diesel engines. A much more in depth article is in the Donaldson muffler catalog (
www.donaldson.com). The Donaldson on-line catalog has a multi page section with charts/diagrams/photos featuring every possible element of muffler construction, muffler regulation, muffler history through the years and even has the math formulas needed to DIY compute muffler back pressure, muffler flow rates and muffler decible levels. Good stuff. -Dean