| A few weeks ago I started noticing an exhaust leak on the driver's side of the engine and after some inspection found that the two nuts on the rear-most port had backed off. I decided to pull the motor to address this as well as installing new bearings into the bottom end as I'm up at 48,000 miles now and I've been replacing them every 15K miles. After removing the manifolds and inspecting them I discovered a small crack in both of them in nearly identical locations - on the backside of the collector where it attaches to the turbine flange - a split reaching across the tube along that narrower side of the rectangular port at the turbine flange. I had them sand blasted to prep them for welding and TIG'd in some 347SS rod to repair it. After some thought it appears that the fatigue failure is a result of the turbine flange and rear head flange being joined together. This bracketing doesn't allow the short tube runner to expand and contract freely. I joined these two flanges out of concern of having the weight of the turbo hanging on the tubes - the joining bracket carries the load to the rear port flange bolted to the head. So I cut these joiners out of both manifolds - the tubing will now have to carry the weight of the turbo. We shall see what happens over time. When I originally built these manifolds there was some debate on using gusset reinforcements between the tube and head flange. Failures at this weld joint were wrecking a lot of the SZ inco manifolds back then. Unfortunately neither of the manifolds have cracks at these locations so the jury is still out on that one.
I've ceramic coated the manifolds using that VHT aerosol product you can get at Advance Auto Parts. I've used this product extensively in our permanent molds used to cast our MASSIVE sidemount endtanks. We pour the alloy at ~1250F and this high temp coating holds up exceptionally well. It helps to insulate the molten aluminum from the steel mold which lowers the pouring temperature required to prevent the metal from solidifying before it fully fills the mold cavity. Lower pouring temp also reduces metal porosity. A single coating of this VHT material will remain intact and functional over 20+ pours. We also use it on the outside of the steel molds to protect the metal from oxidation. So I applied this to the manifold's exterior solely to reduce the oxidation of the material. Alloy 321 is a stabilized stainless steel which offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). Alloy 321 stainless steel is stabilized against chromium carbide formation by the addition of titanium. Even still, over hundreds of heat cycles and exposure to these elevated temps, the material still oxidizes a bit. Alloy 321 stainless steel is also advantageous for high temperature service because of its good mechanical properties. Alloy 321 stainless steel has higher creep and stress rupture properties than Alloy 304 and 304L. It is an excellent material to use for turbo exhaust manifold construction and doesn't carry the huge financial penalty associated with using Inconel. Even still, I've got nearly $650 tied up in the materials. After welding expenses and heat treating they totaled around $1000, about half of what the inco manis were at the time. These days with the availability of cast iron manifolds for dirt cheap (comparatively) the tubular approach is obviously not the way to go. However, when I built these manifolds in 2005 we didn't have options like we do today. So, with that said, on to the flowtest results. Admittedly I was a bit disappointed as they didn't perform quite as well as I expected but I've got the data no less. Here's a comparison vs. the MS manifolds I flowtested some time ago:
 
Even despite the results not meeting my expectations, it does raise questions. I've been able to produce 693RWHP and 640RWTQ with my setup - 565RWHP on pumpfuel at 18psi. There's certainly no shortage of power and doing this with 60mm compressors and T28 turbines. My thoughts go directly to the turbine and housing with this info. So, I'll be flowtesting a turbine housing to see how it performs. There's only so much benefit you can get from opening the exhaust manifolds since there's a turbocharger directly downstream of it with a housing that funnels the gases through a rather small annulus leading to the turbine. If the turbine section is more restrictive than the manifold runners then there's really not much you can do to the manifolds to improve flow. I'll report back on this once I've done the testing. In addition, I will be flowtesting a set of stock turbo inlet pipes and accordion sections to get a good baseline on them to use for developing performance replacements. Will have that on Monday/Tuesday. :)
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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AshsZ-II Ultimate Street Z - Manifold Flowtest >>>> - 
