You might get away with a BNR S1 without retuning.
The problem is your stock tune is based on the boost response of the stock turbo.
If you have a turbo that spools differently and is more efficient you could end up with boost spikes and overboosting.
The HPFP are marginal on these cars with the stock turbo and tune. With any higher performance turbo you will need HPFP internals upgraded.
The fluttering could be your turbo vanes scraping the casing. If you can get the inlet pipe off you can feel how much lateral play is in the turbo shaft by hand.
There is a local Mazda tech who does the timing chain replacements from his home business Laxspeed. I am doing mine myself on my CX7 starting tomorrow, wish me luck.
CX7 - The younger, taller and sexier replacement for the MPS6 and the first car designed around the MZR DISI
2007 CX7 2.3 DISI AWD Ice Blue | HID's | ETS TMIC | Cobb XLE BOV | CX9 20" wheels | 245/50/20 Scorpion STR's | CS HPFP | CX9 Brakes | Pedders Sports Ryders -40mm | CS Turbo | JBR 3.5" WPI | Cooling Mist WMI |Versatune