Quote:
Originally Posted by LuckyX2
Yes, inertia is linear with mass and quadratic with radius but even so that still means BW's claimed halving of mass allows them to make the turbines 1.4x larger and have the same inertia. A 40% increase in turbine size at no inertial cost is pretty dramatic to me. But this is also assuming the material is distributed the same in the turbine design. If BW's wheels have more material at the edges than Garrett's then obviously some of that advantage is lost. Even so, a 10-20% increase in turbine size would still be a formidable benefit. Combine that with the new geometry and twin scroll housing and I don't think anyone has anything to match the 7163.
Where are these comparisons you've seen? I've only seen a handful of comparisons with the first gen stuff and next to nothing on the 7163.
Edit: Found a GTX vs GT comparison
Looks like the GTX isn't much better than the GT. The 7163 that Perrin tested would still beat it pretty handily below 3500 and be about equal above there.
And if anything, the GTX spools slightly later. That makes sense considering they have a more aggressive compressor but the same turbine powering it from the GT. |
The GTX3076R is a crap turbo, as the GT3076R was already a compressor/turbine mismatch, and putting even MORE compressor on the small 60 mm turbine is just not going to go well. Of course it spools up slowly and barely outpowers it. Get to a more reasonable compressor/turbine wheel speed ratio like the GT3071R to GTX3071R and a better story emerges.
As for TiAl wheels - it's not just all a huge party. The turbine wheels need a larger cross sectional area on the blades to handle the stress since it is a weaker material at high temps than the very nice 718 Inconel of Garrett wheels. Ideally you'd have an infinitely thin turbine blade, so having a thicker blade cuts into your turbine efficiency. To combat this BW went with a full back plate on the turbine wheel like you see on compressor wheels. This enhances efficiency at the expense of a lot of inertia, and also helps give structural stability to the blades by supporting their back end. This all sums up to way more inertia than simple weight measurements would indicate, and a slight hit to turbine efficiency. Which probably explains why most EFR designs are going with higher turbine wheel major and minor diameters for the same "power" compressor wheels vs. the GTX lineup.
This is some good info on TiAl wheels (and other good info on speed ratios, and steady vs. unsteady behavior):
On Mixed Flow Turbines for Automotive Turbocharger Applications