Quoting grocery_getter:
I was waiting for this to come up. Here is the problem with installing those bigger flapper valve. With the bigger valve, and a bigger hole, it is easier for exhaust flow pressure to push open the valve and bleed boost once you are above 22-24psi. On a boost graph, you can see a steady boost and then boost will start going down noticeably on the top end.
I'd say the ideal solution is to fuel it. Don't put an evo3 16G on a straight thru 3" turbo back exhaust if you don't have the fuel for it yet. It will creep and it will lean out. So the stock fuel system will not handle 24psi out of an evo3 16G, so add fuel to the equation. Instead of spending time and money curbing boost or avoiding boost creep, embrace the boost!!! Spend money upgrading the fuel side, get a good boost controller, fuel parts, fuel management and actually run it up there and get power as a dividend.
You can do all the trick to eliminate boost creep and have a steady boost but all those time and money that you spent "fixing" boost creep is for what? To run less boost and less power? Did I hear that right? You are spending money to run less power? Better spent buying a fuel pump and big injector. So if life gives you a lemon, make lemonade! If you are going to spend money, by God, spend it to go faster not slower.
That Andre is what i wanted to hear, apart from the 3" o2 back, my fuel system except the rail and injectors are ready. i've been looking into the evo8 ecu swap and plan to run a slightly tweaked base tune, stock e8 injectors, maf, ect. i think this will be adequate in combating said lean out issues, what do you guys think?