A couple of things:
theman352001 spooling is not necessarily the problem, for instance when gear changing the turbine/impellor can actually spin faster because it isn't doing much work, it's stall that causes the problem. The stall occurs after stall flutter and is the air stream breaking away from the blade contours; the compressor impellor does not actually physically stall, the air does.
Godlaus there are lots of ways to reduce lag. The most obvious method is to make a hybrid that suits the application. Other common things are dump pipes, long radius up pipes, plenum resizing, etc. A method some of us use is to run the fueling lean at lower revs in certain circumstances so that the throttle is more open and flow through the turbine higher, thus earlier spooling.
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