***How to Choose an Exhaust System***

[bairjo]

I just want a longer lasting replacement.

[fnkngrv]

Originally Posted by bairjo

I just want a longer lasting replacement.

My preference is T409 rather than T304. When I was at Miami Muffler back in 2011 they showed me the difference between the two after a few years and the T409 tends to have less likelihood of cracking due to the way they form the piping. T304 is supposedly the highest grade however they also showed me that for the most part this is a marketing thing. It costs more therefore they want you to buy it over T409 most times. T304 is less tolerant to heat from what they shared. I went with T409 and my piping looks like it did when it was installed in June 2011 and that is with running boost and living in Northern Maine. Just my 2 cents. I would also go with a mandrel bent custom setup and just be done with it. It was also cheaper for me that that. Who knows...I may actually have to ditch the one that I have since I will be running so much boost and hp. I had never thought that I would need bigger than 2.5". I may have been mistaken.

[bairjo]

So is that a draw back to stainless...cracking? It doesn't rust but cracks? I ask this due to what you said along with my experience with my stainless gas grill burners. I use the grill all year, cold weather and hot, and they always crack and fail in a year. Yes, they are not the best grade of stainless, but amplify things on an exhaust system and now im starting to have second thoughts.

[xnamerxx]

Stainless has bad thermal conductivity, and it has bad thermal expansion characteristics comparison to mild steel. The reason it cracks can be due to many things, but mostly because of a product design problem. Since steel expands slightly when heated, if that isn't taken into account when designing the product, it will fatigue and fail.
You'll notice alot of aftermarket headers do this as well Miatas specifically, and it almost always happens at where the metal is joined together, and thats specifically because the weld is more brittle compared the surrounding metal making them less ductile. So to get around this you can use thicker material, that can handle more stress compared to a thinner material.
If you want a fun experiment watch a truck climb up a steep grade at night, you'll see a glow underneath the car because the header is probably 900-1600 degrees, and thats the typical heat range a header is expected to operate in, whereas further down the exhaust stream you may only be seeing 200 degrees.

So in essense what I'm getting at is, nothing else out there is going to be as durable as the stock exhaust. Its made of 409ss and double walled, its sufficiently thick and has been properly designed to without the stresses of driving.

[bairjo]

Thank you xnamerxx. Sounds like you know metalurgy. But when you are saying the stock exhaust, are you saying the Yaris exhaust is already stainless? You have to understand...I'm not very bright.

[xnamerxx]

Stock exhaust is stainless for sure. It's made of out 409ss, its not quite as corrosion resistant, and will develop surface rust. Hence why its that brown color.

Since OEMs have to warranty their exhaust for 10 years of weather and salt, they need to use a material that's capable of withstanding that with a semi low rate of failure. So that means they can't use any grades of carbon steel, so low grades of stainless steel are cheap enough while offering enough weather resistance to last through the warranty period.

[bairjo]

Thank you for clarifying that...guess I'll hold of on any exhaust upgrade for now. Thanks again. You got to love Yarisworld...ask the question and you will get an answer from someone that knows his shit..er exhaust.