Mike Rainbird I'm told that you can get a couple bhp more then 320 but not much. Most of the difference is due to getting higher heat efficcency and using oxygen which is bound in fuel particles. But it won't make much difference.

I don't know if anbody experimented with this a lot but I would expect that with "bilion pound budget" thry wuld still make zilion horsepower if restrictor were fittted bedind the turbo.