HI,

What would be the effect of installing a slightly smaller compressor wheel inside of a turbo? Normal tip clearance is supposed to be within 1 mm. So what if you put in a smaller impeller that gave a 5mm tip clearance gap.

I was reading a paper on the effects of the impeller gap on turbines. They noted that with a larger gap there is less efficiency, however; the larger gap also reduces noise and vibration.

So if I had a turbo that was rated for 22 psi Max and I changed the compress side to smaller turbine in it would it still boost with the large gap to a lower psi? How much efficiency do you think would be lost?

 

Noise and vibration go away because the blade loading differential and tip vortices go away.

You'll gain flow up top, but lose the bottom end as the inducer cannot feed the wheel like its supposed to.

Inefficiencies go up squared. So double the gap, quadruple the loss.

There's better ways to achieve the same thing, which is mostly a deep groove right at the tips. Problem is water can accumulate there, either from pcv or condensation. If you live in a cold climate it's very well documented the water freezes to the blade tips and bends them. Although that is usually on the billet wheels that have thinner blade profiles.