Anyone know how much power an exhaust mounted turbine (turbocharger minus the compressor) can generate at the shaft? Say the amount necessary to generate 1 bar of boost with a compressor?

I've had one suggestion that around 2lbft at 80,000rpm (around 30bhp) would be a reasonable expectation? Does this sound about right?

If the engine is designed to run NA and the output of the turbine is used for other purposes, does the turbine itself become a big parasitic loss to engine output or is it still essentially recovering energy from spent exhaust gases that would otherwise be dissipated to the atmosphere?

TIA for any input!