[Fendamonky]

The basic reliability mods like AST, all metal Radiator, removing the pre-cat, etc., etc. are always the first thing you'll want to do with an FD if it's not done already since they are cheap and (at this point) going on 20 years old.

Once you start pushing for power you'll see immense benefits from fitting a Water Injection system though. The reason being is that as you boost you will be spraying water into the combustion chamber. Not only will that have the immediate effect of cooling the intake temperatures and combating (damned near eliminating) pre-detonation, but it will also be essentially steam cleaning your engine internals. Running water injection is an excellent way to constantly remove carbon build-up.

A stock AST may break, a stock radiator may spring a leak, a stock (USDM) precat will cook the engine bay... Excessive carbon build up WILL ALWAYS lead to a rebuild one way or another.

Also, an alternate method (if Water Injection is not an option for whatever reason) is to feed your car distilled water as a matter of maintenance, say on a quarterly schedule.

Essentially all you do there is get yourself a gallon of distilled (possibly labeled as "demineralized") water from the grocery store, swing by the local auto parts store and get yourself a length of windshield wiper hose and a "T" fitting. Cut two 6"-8" sections from the end of the wiper hose and fit them to either end of the "T" connector, stick the longer hose to bottom of the fitting. Uncap the two nipples on your UIM (one should feed the front rotor housing, the other to the rear) and fit the two shorter hoses over the nipples. Stick the longer hose into the gallon of water then hold your RPMs steady at 3-4krpms (enough to keep the engine from dying, not so much to come into boost though) and let the vacuum draw in all the water.

The engine will start bucking, kick out a ton of smoke, and be REAL loud and pissed sounding when it's sucking in the water but that's ok. It's damned near impossible to hydrolock a rotary, so you're not likely to damage the engine (unless it's already fucked, and removing the carbon makes that damage apparent) while doing this. Once the water is all gone you're good to go. I'd suggest making sure the car is fully warmed up before doing it (go for an aggressive 20 minute drive before doing it), then taking the car out immediately after you're done for another spirited drive to make sure you get everything cleared out.