Stainless Steel Exhaust System: 304 or 409?

Thousands of exhaust systems are being replaced annually in Australia, which is to be expected given the fact that most, if not all stock exhaust systems are made of materials unsuitable for the job, such as mild steel. That being said, if you’re looking for a stock exhaust replacement, then you might as well make a long-term investment, and pay a higher initial price, but get more value out of it in the long run.

The reason why stock exhaust systems are made of non-suitable materials, is because they’re made to be affordable, so that the overall price of the vehicle is lower. On the other hand, an aftermarket stainless steel exhaust system is made with durability and quality in mind. However, not even every stainless steel exhaust system is made the same.

You’ll find two popular types of stainless steel exhaust systems, and they go by the numbers 304 and 409. There are a couple of differences between both types, which you might not be able to tell just by looking at them. For instance, the corrosion resistance properties might not be the same, as both types have a different amount of nickel and chromium in the alloy.

409 is designed specifically for the exhaust industry, although it can be used for other industrial purposes as well. The main reason why 409 is so popular is because it combines strength, a decent amount of temperature and corrosion resistance, yet is relatively inexpensive. It’s the most common material which aftermarket exhaust systems are made of, and typically has 10.5% to 11.75% chromium and 0.5% nickel in its alloy.

304, on the other hand, is one of the oldest variants of stainless steel alloys and it’s one of the most commonly used alloys to this very day. 304 is the highest quality of stainless steel alloy for exhausts, and it’s used whenever strength is of utmost importance. Moreover, it’s incredibly tough and rust-resistant and the alloy typically contains 20% chromium and 10% nickel. However, when exposed to heat, it can develop a golden colour over time, because of its low ferrous content.

Simply put, both 304 and 409 stainless steel systems will significantly outperform your stock exhaust in every single way: air flow, fuel economy, more horsepower and throttle, and the main difference between them is their durability, which the 304 is better at, but it all comes at a price. Even the 409 will likely last you for many years, and it very well might outlast your vehicle’s life span.