Turbine impeller machining

[Billman]

I was looking again at the pictures of James Bufkin and I while I new it is done by many people I never given any thought there.

What is it with the machining of the turbine impeller nut?
Does it reduce the weight that much that it is worth?
Does it make balancing difficult?

take a look at those pictures and comment please.

Here as on SQ K27:



and then machined also

[mcandmar]

I think its part of the balancing process..

[Billman]

No, not in that extent.

[AndyP]

The top one, where it's just machined on one edge I would say is balancing. The others that are machined in the middle I would say are for lightening, taken to the extreme!

[Billman]

Yes the first one is not machined for "enhancement" but for balancing. It is clear. But does anyone has any data as to how much does this kind of machining improve spool up on a mid frame turbo?

[quattro84]

It's neglectable, inertia equals mass times squared radius, so mass that close to the center of rotation does not contribute that much.