I decided to have a play with my car again and give myself an excuse to make a few things on my lathe !
I did have a bleed valve fitted on my car a while ago but after the boost going high after removing the cat I decided to take it off.
I had to put the cat back for the MOT and it's been there since so I thought it might be worth having a play again.
Before trying various things before I read loads about what others had done. Bleed valves that allow a certain amount of pressurised air to escape were the most popular method. People have then started favouring adjustable ball valves. It's this type most commonly made from pneumatic/plumbing fittings seen for sale on ebay.
This is one of them for example.
While this type seems to work very well they need to have some sort of vent to allow the wastegate actuator to return quickly after it opens. Most I have seen don't have this and rely on leaks from the adjustment screw to work properly. I tried drilling a very small hole in one of the fittings which seemed to work. When I tested it on the car the boost semed very on or off which is fine if all you want is instant power but not very nice to drive around town.