The typical bolt on build would be RRE header, RRE underdrive pulley, DC sports cold air intake, 2.25-2.5" exhaust, and a 91 tune. Goes from about 140-145whp to 175-180whp generally on a healthy motor.
Turbo wise, GT28/GT30 or precision 56-60mm are a common go.
Internals wise, I've got a 4G69 bottom end kit for about 700hp.
Manifold, Fernando Motorsport (FMS) makes a very nice one with T3 or T4 flanges. A basic log manifold will be coming on the market very soon, they're just setting up production method and pricing. It's to be a cheap entry to turbo.
FI tuning is on pause with factory ECU right now due to long delays in software setup by the maker of the software I use. Standalone is the only reasonable option. Piggyback can't fuel properly as they can't remove some vacuum reference stuff in the ECU for fuel injector pulse offsetting. Has led to many headaches and some blown motors over the years.
NA tuning is available.
Stock MAF housing can handle about 340whp. Stock motor you'll be topped out around there anyway with safe-ish tuning if the motor is healthy.
Stock clutch will hold fine to bolt ons, but not FI. FX350 from clutch masters is good to about 15-20lbs boost depending on setup. FX400 I've run to ~500whp. I haven't got the turbo flow to go much farther for testing.
Stock fuel system is good to about 230hp. Bigger injectors, you can get past 300whp on the stock pump. Stock pump is ~240lph.
There are compact drop in pumps which work. I run an AEM 340lph pump in my GS with a return fueling conversion. A lot of people suggest the Deatchwerks 255lph. It'll fit, and can use the factory regulator and wiring. Because it's almost no change from stock and a waste of money.
LSD are a tricky one to find for these. Wavetrac and Quaife used to make them. Stock GS manual dif is open, but can hold up to about 600hp. Lancer ralliart guys for contrast usually see issues around 400.
Input shaft bearings are a deep groove ball bearing. They should be a roller bearing instead. I'm trying to get something custom made without success just yet. Ball bearings can't take the thrust load, and the cages wear and fall apart. Mitsubishi knew about this issue in design in 2005. They blame it on hard launches. Happens on the Evo more commonly for the same reason. Offered no fix.
Timing belts on these are great, as they protect the engine better than a chain at high revs. But being a belt, they do of course need to be replaced more often. By this point, every 4g should be on its second or 3rd belt depending on year alone. Mileage and use affects it as well.
As for oil, the cap says 5w-20. If you check the owner's manual section, you'll find different oil viscosities based on use. 5w-20 is no good for hard use, which basically is anything in the 4000+ rpm range when the VVT engages. Plenty of people have wrecked oil pumps and bearings at the track running 5w-20. Some in only a few laps. GT are worse for this, but GS are not exempt. The bearings are identical to an Evo 8/9, which does not run 5w-20. 5w-30 is the suggested oil unless you're babying the car.
That should be a nice intro to the platform for someone looking to mod.
