Rev hanging was a hot topic a few years ago and restrictor plates appeared to offer a solution although I went down a different route. On my Blacktop Zetec I replaced the exhaust manifold with a less restrictive version a 200 cell cat and a free flowing exhaust, Librands set up, and the rev hanging disappeared and I have a very responsive engine that is a joy to drive. Not a cheap solution but it transformed the car.
