The various grades of 300 Series Stainless Steel have long been used for aircraft intake and exhaust systems due to their high strength, excellent heat tolerance, and corrosion resistance.

304 Stainless Steel tubing is generally used for intake systems and relatively low temperature exhaust components, such as extension tubes and muffler shrouds. 304 is used when corrosion resistance is required but high temperatures are not encountered. 304 is also the most extensively used austenitic grade due to it's use in automotive and industrial applications and therefore is the least expensive grade.

321 Stainless is the most commonly-used material grade for primary aircraft exhaust system components. It combines excellent ductility with high temperature strength and corrosion resistance. 321 maintains it's strength in applications that exceed 1600degF for prolonged periods. We use 321 extensively for our exhaust systems as well as many of the critical formed bends that we produce.

347 Stainless material maintains the high temperature strength of 321, but differs from 321 in that it is further stabilized against chromium carbide precipitation by the addition of niobium and tantalum. 347 material is sometimes specified for turbine/compressor discharge tubes and other cost-is-no-object applications.

Grade 2 Titanium tubing has some very enticing properties - approximately 55% lighter than stainless, similar strength qualities, and resistance to corrosion. But unfortunately, Titanium loses it's strength quickly as high temperatures are encountered. The use of titanium tubing as a primary exhaust section leads to stress fractures in very little time. Titanium also has almost twice the degree of thermal conductivity as stainless, so heat more readily transfers through the material and onto the surrounding components. Also, like aluminum, titanium alloy endures only small amounts of elongation before failure which makes the material very difficult to form.

Inconel 625 tubing is another intriguing alloy used in severe duty, ultra-high temperature applications. With a general temperature rating that exceeds 1800 degrees Fahrenheit, it's high temperature strength properties exceed 321 and 347 Stainless while matching it's corrosion resistance. In theory this sounds great, but how often do your lean-of-peak EGT readings exceed even 1550°? And best power mixture is generally in the 1350°F range...Then factor in the price of the material at close to $10USD per inch as well as it's comparatively higher weight than stainless and it's easy to see why it is inefficient to use on naturally aspirated, piston engines.