>> while the the engine revs too low for the turbo to kick in?

This is a common misconception of 'turbo lag'. A modern turbo is actually operating at the low revs too. The boost is there. But a modern turbo engine, especially a diesel, has a very narrow powerband, giving the impression that the turbo isn't active until higher rpms. This isn't real 'turbo lag'. Real 'turbo lag' is the delay caused by the fact that the turbo depends on exhaust pressures, which rise only momentarily after throttle increases. But this problem has largely been solved via mutli-stage turbos, lighter turbo parts, waste gates and the like. Real turbo lag, where it is noticeable, occurs at all rpm ranges.