Cooling management is one of the biggest things to consider with grip racing these chassis, along with utilising the advancements in grip that drifting has brought about. The chassis is over powered easily IMO, hence the suitability for drifting. However it is relatively easily to make them grip up and fly around circuits.
An external engine oil cooler is a big necessity, along with accurate gauges showing oil pressure, oil temp and coolant temp (and exhaust temp if you can). Look to get an aftermarket ECU to ensure mixtures are correct with the modifications you've done, with it in mind you want to err on the side of a safe tune as you'll be pushing the engine hard for extended periods at a time. You won't need the added features of a Link, but a Nistune would be perfect.
Expect things like coilpacks to die due to the heat experienced in circuit racing. Make sure there is a flexi join in the exhaust and combined with properly bracing the turbo it is the BEST thing you can do to stop the turbo-manifold nuts backing off (a constant source of problems with SR's). Do it before it happens and you'll thank yourself later.
Running fully synthetic gearbox oil and ensuring the gearbox is sealed well is important. If you can find a way to keep the gearbox oil from boiling then do that (not sure if gearbox coolers are available sorry)
A mate Elliot grip raced his S14 and it was very competitive but had issues with gearbox oil overheating and coming out the shifter hole:
https://www.youtube.com/channel/UC-mpTKGVRHOPqpAZHOf7ZIA
Drilled and slotted front brake discs are needed as getting rid of heat is a big requirement. Along with running the best brake fluid you can afford. Look to duct air from the front bar to the discs to help and keep an eye out for upgraded front calipers and BMC in the future (ideally R33 GTST/Z32 or similar)
A full suspension bushing replacement is also a necessity to reduce flex (but not eliminate it), especially steering rack bushes, rear subframe bushes, engine mounts and rear camber & toe arm bushes - these experience the highest loads in circuit racing on these chassis (plus front ball joints). Don't bother with expensive swaybars at this stage, you want a relatively soft one in the rear, and the front will be tight enough with the HSD's
Tyres will make or break it - look to run at least a 235 up front and a 265 out the back. Look to run a semi slick that can handle being heat cycled regularly, but be aware tyres will be a big expense. Only expect them to last 2-3 track days at a time. Michelin's, Toyo's and Nitto's are widely used, but to start off i would recommend a cheaper semi slick like Westlakes as they can take a beating while you're learning the rest of the car
For the future look out for a 1.5 way mechanical diff as the viscous will eventually degrade and act like an open
Also consider running rear drop knuckles in order to get the suspension working as good as it can. Drop knuckles up front are not as critical, especially as i don't imagine the car will be running low ride heights with grip in mind
While learning keep an eye on your gauges, hopefully get a set with warning lights. Change the oil after every second event and check the filter for bearing material - you want to give the engine the best chance to survive the conditions
But if you set up an RPS13 with the above things done and you'll have a package to scare the shit out of some seriously fast factory cars
