I am not trying to be disagreeable with whoever told you that, but it certainly looks like the top of the blades were ground down or clipped. Here is a picture of a similar 9-blade TD06H turbine wheel of a similar design puled out of a failed turbo a customer sent in. The top of the blades are not clipped. The difference should look obvious.
Clipping is an old-school hack. It can increase the turbine section flow, but kind of wrecks the areo of the turbine wheel. It basically make it much less efficient. Normally improved flow does not offset the drop in efficiency performance wise. The trick can workout sometimes if you are stuck with say the OEM turbine wheel and housing, and are adding a high flow comp wheel. Anyway, if you are making a new turbine wheel anyway, you can just size it correctly such that it flow well enough without clipping. You get the flow you need, and keep the wheels efficiency.
As a side note, we also use similar 9-blade turbines in our STI turbos. We have also gas bench tested them and have compressor and turbine maps for them which we posted below.
Pros for the 9-blade turbine wheel like this:
- low mass = low moment of inertia = faster response
- tiny hubs = low mass & more blade area
- flow great for size
Cons:
- poor efficiency (52% vs Garrett's 72%)
- low harmonic frequency = potentially lower RPM potential and durablity
- tiny hub = high blade failure risk due to stress at the junction of the blade to the hub
With all of that said, they worked well for our JB STI turbos, so we continue to use them.
-Sam
https://blog.steamspeed.com/2015/03/12/steam-stx-71-flow-testing-part-2-stx-71-vs-gtx3071r/
