Because the manifold is so short and the pipe is so thin, the manifold gets hot really fast.... This offers amazing spool up, but the problem is you can only bend a paper clip back and forth so many times before it breaks..... It comes down to a material being able to thermal cycle a given number of times at a given temperature. The higher the temperature the lower the number of times it can heat cycle before failure. Because the stock size manifold is so short it offers superior spool over a longer manifold, with the thickness of a cast manifold the manifold does not get too hot to quickly and a cast manifold will operate in a range where it will live a long life......A thin tube manifold will glow red by 3500 RPM as short as the 300zx manifold is.....This heat causes the manifold to grow or expand. When we made manifolds nothing else was available for the car to fit in the stock configuration. We tested several sets of 304 stainless manifolds and 321 stainless manifolds. The 304 cracked the material in a few weeks. The 304 lasted several races and street driving for a few months. We do the testing on our own cars and found they failed too easy and never sold any in the 304 or 321 stainless. We found a guy making Inconel Manifolds for NASCAR and had him build Inconel manifolds for us. These were still working well on my own car after a year of racing with N20 and street driving and we went ahead and started producing them. Because it was a better material it did last longer, but over time they do fail and the higher the temp the sooner they fail. At pump octane boost and having 3" exhaust some have still not cracked. Because of the short length of the manifolds on eBay they will fail. They will also fail soon because they can not be making them from a material that can handle any heat as the material itself would cost much more than the sale price of the unit they are selling.
