DailyDriverMods
Member
- Joined
- Aug 23, 2020
- Location
- Netherlands
The short version is that the TiAL turbine flows a tad less than the Inconel one. This causes higher backpressure which resulted into retarded ignition timing during the tests in order to prevent knock. That's why the torque numbers are a little lower. Now they also stated that the flow difference between the two turbine wheels is so small that it's considered "not significant".I think I read this report. I think there was something to do with the shape of the blades or something like that. If it's the same test, there was some nuances about the differences that didn't come down to just weight, but the materials used also allowed/did not allow some changes to the overall design of the impeller. Maybe one had thicker blades? Dang I can't remember.
The small difference between the turbine wheels comes from the usage of different materials, TiAL is lighter but also weaker than Inconel. Because of this the TiAL turbine wheel needs a slightly tweaked design, most importantly it needs thicker blades. This generally reduces turbine efficiency by a smidge but can be (partially) compensated for by tweaking the rest of the design.
And that's what you're seeing here i think. It's not that both turbines are already at choke flow at these 2000rpm tests, it's more like the TiAL turbine wheel is a little less efficient and needs a smidge higher pressure ratio thus reducing flow. Insignificant on itself but on the knock limited 2.0 GDI engine it seemingly makes a visible difference when using the stock ECU.