In the end, I think you still have the same restictive muffler, so the gains won't entirely be there. I still have my stock racing beat attached (but much bigger piping going to it). It works, but I will be replacing it soon, it is just too small and restrictive. I'd love to be able to do a before and after dyno, but that is unlikely.
So, yes you can do it, yes, you'll see some gains as you eliminate some restriction by the other mods, but if the final "hole" it has to come out is the same, you won't "break through" until you change that.
You will get some "popping" sounds and such since the air is going to be "confused" due to size changes and such, and could theoretically cause more backpressure, but I'd love to meet the engineer that can answer that just from the info you've given. Mind you, I know plenty that will try, but I also know plenty that I'm afraid to call "brothers".
Damn, sorry, I must be cranky today.
I've basically done what you're asking, so it is possible, but I cannot answer if there were any gains from that. Other than I did the turbo at the same time. So, Woooahh! Big difference!
