I ran a dp, cat back, and intake on the stock ecu for a while and everything was ok. I later bought a boost controller and a power fc to be safe. I'm using a Greddy Ti cat-back and a Blitz sus intake with no boost spikes.

 

With stock ecu, I highly recommend putting back your main catalytic convertor, and fit a cat back. I have a Japan spec 1995 FD, comes with downpipe from factory, and added an RB dual tip catback, a greddy sm intercooler, efini y-pipe and took off the rubber seal between stock airbox and intake snorkel. That's the limit of mods I could do before boost spikes over 11.5psi at which I get 310bhp. Even if I replace the stock paper filter with a K&N drop in, boost will spike to over 12psi. I am not sure the stock ecu mapping for my FD is the same as yours, but with a mid pipe you are most probably going to run into trouble.

 

We agree on the basics....putting the cat back on. But understand that a midpipe causes boost CREEP, which is different than boost SPIKE. While both can lead to detonation, Spike can be contolled by a good BC. I think the only thing you can do for creep is to port the waste-gate or restore some exhaust restriction (i.e. reinstall the cat).