Hey Guys,


I have a question about then stainless used on manifolds. Most stainless I have seen used is 304 including Lovefab, full race. There is a company here in town that uses schd 40 piping for their manifolds. My uncle told me to use 321 stainless. The whole idea to use the 321 comes from the flaking concept. I guess this means where the stainless flakes on the inside of the manifold and then goes into turbo which equals boom. Anyways, I guess my main question is has anyone had problems with flaking in their manifolds. Apparently, when 304 stainless was available at a cheap price in the past, the porsche 930 owners would continually blow up their turbos???

Any suggestions would be helpful.

 

I've heard the same about it flaking in general when exposed to heat stresses ..... anyone have details?

I'm about to have custom stainless done myself so I'm worried too

 

There is a major price difference in the two because the 321 has some titanium in it. In addition, has anyone dealt with Burns Stainless?

 

^ My engineer goes to the trouble of sourcing his steel and aluminium piping from Burns, and he lives in Malta...

 

As mentioned, 321 is a Ti stabilized grade of stainless. The Ti is used to avoid issues with intergranular corrosion attack, 'IGA'. The problem with IGA happens in the heat affected zone, HAZ, of the weld. The carbon in the non stabilized 304 combines with the chrome and forms Cr carbides. This effectively removes chrome from the grain boundaries in the HAZ. As a result those grain boundaries are subjected to attack by corrosion. With 321 the carbon is tied up with the titanium to form Ti carbides. As such the HAZ is not depleted of chrome.

Have you ever seen a muffler with a crack around the perimeter of the weld? Most people think the weld has failed. In most cases it is due to IGA. A lot of manufacturers will tell you it is due to poor installation. I went through that once until I sectioned the welds and showed them the real problem.

Many people have no idea of what they are really working with. My melt code list at work shows in excess of 30 grades of 304!

As to flaking, the surface of the stainless oxidizes at elevated temperatures and forms an oxide. This oxide can flake off after repeated cycles. However, we are not talking about large chunks. It would be very small and with very little mass. Not enough to harm an impeller, IMO.

 

Alan