Stainless steel is a common term that represents a wide range of alloy steels. It was developed to satisfy the industry's demand for steels with high mechnical properties and physical constants under high heat, acid and corrosive conditions. Today, it accounts for more than 50% of all steel produced.

1. t 410
11.50 - 13.50
2. t 409
10.50 - 11.75
3. t 304
18.00 - 20.00
8.00 - 10.00

The outstanding characteristic of stainless steels is their ability to readily form a chromium film, which acts as a constant buffer against corrosion. This film is quite stable and if broken or destroyed, will reform instantly and continue its protective action. The higher the chromium content, the greater the corrosion resistance.  Nickel additions in stainless steel profoundly affect the resulting steel. They act as a supplementary to chromium thus producing a product even more corrosive resistant. If the alloy contains sufficient nickel, the steel becomes non-magnetic and non-hardening under high temperatures providing optimum strength-to-weight ratio for forming, bending and welding applications. Yet, stainless is more brittle than mild steel, so make sure, if you are using it for an exhaust system, that it is held along its length by rubber which is checked often. If the system is held too rigidly, it can break when hot, or worse, allow the impact to travel up to the manifolds and damage the heads. When steel bolts are used in aluminium, the steel will always win. Additionally, the rubber "doughnuts" at the rear that Morgan uses on coat hangers wear rapidly and soon announced their failure when turning. Kevin Vernon and I came up with a more reliable and attractive solution pictured here. 

A good stainless exhaust system will use 16 gauge, T304 stainless. Many suppliers, Morgan dealers as well, will use inferior qualities so buyer beware!

Frankly, a better option for manifolds is mild steel ceramacoated inside and out. They also do not rust, can withstand impact, flow the gases faster and have greater flexibility and they do not discolour after the first usage. Sadly, there is more profit in stainless steel exhausts and mild steel has become rare. The best option is to ceramacoat the stainless steel manifolds.

Flex pipes 
are used primarily as a cost saver rather than crafting a fully bespoke system. They prevent the exhaust parts of the system from cracking they can take up the flexing movement of the components of the car. However, they don't flow as well as a normal pipe so one must expect a power loss and the public  preception of making do BUT they are better than having a cracked header/ manifold and other components. Beware as they will deteriorate faster than the rest of the system. A small section of flex pipe never hurt anyone outside a Concours competition.