I understand Garrett (the Turbo manufacturer) is working on a 3 turbo system. One turbo running the whole time, one for low revs and this will cut out when the turbo for high revs cuts in. The idea is to reduce any turbo lag and make acceleration smoother through the rev range. Just thought some of you may be interested.

 

Think of the heat generated by 3 turbos under the bonnet!

The one designed to provide boost at higher revs will still need to be big to be able to give the required throughput, though the others could no doubt be much smaller.