I am new to modifying anything Diesel always been a petrol head. I have a 2013 GU Y61 and I was wondering if I would benefit from fitting a Dawes Valve and Needle valve?
I have a EGR plate to install, a catch can, Pre Fuel Filter, EGT gauge and Boost gauge do I need the Dawes etc??
Taking away control of variable geometry turbocharger from the engine ECU is great improvement to overall performance.
Removing VNT control you need to limit your boost somehow and that's where Dawes valve comes in, indeed I recommend going for a local solution called Tillix valve. A needle valve is there to slow down the rate of turbo spoolup, I actually drove mine for a while with the needle valve fully closed (not functioning) and the low down turbo spool up was phenomenal except I decided to play it safe as well as ECU causing limps so I set it up to avoid those.
For performance improvements and reduction in EGTs when cruising on the highway I fully recommend you try them. It will transform the car and you'll be hooked. I don't think I'd ever go back to factory setup on mine for sure, especially if you're considering EGR plate fitted as well which might bring engine check lamp ON (especially on late CrD ZD30)some get away with drilling a small hole in the plate to fool the ECU.
If you need some convincing then test the theory yourself, after fitting EGT gauge (why bother with boost gauge I don't know as you have an access to OBD2 data via a cheap scanner like Scangauge) check the results before (with ECU controlling turbo and after with needle valve/Tillix valve combo.