Tail Pipe Kit- 3in 67-69 GM F-Body Inline Chips & Modules Muffler - Flow FX -

Muffler - Flow FX - 3 in Center Inlet - 3 in Offset Outlet - 14 x 9 x 4 in Oval Body - 39

While the unit could be physically thicker the 40mm dimension was ultimately chosen with consideration of airflow requirements of the main radiator which is located directly behind the heat exchanger

5 in Tips - Stainless - Natural - Ford Mustang 1986-93 - Kit

Exhaust System - Sport - Cat-Back - 3 in Diameter - 4 in Tip - Stainless - Natural - GM LS-Series - GM Fullsize Truck 2010-13 - Kit

With 60% more volume and 19% more face area than stock along with being a whopping 40mm thick (stock is 24mm)

Tail Pipe Kit- 3in 67-69 GM F-Body Inline Chips & Modules Muffler - Flow FX -Exhaust Tailpipe 3 in Diameter Steel Aluminized GM F Body 1967 69 Pair