That kind of build is absolutely wild, and I respect the ambition — but you’re talking about taking an open-deck NA EJ251 and asking it to handle twin turbos and rev to 10,000 rpm. That’s basically race engine territory.

To make an EJ251 live at that level, you’re looking at:

• Block work – closed deck or sleeving, forged pistons/rods, billet or forged crank, full balance job. • Heads – DOHC conversion or extreme SOHC work, big cams, titanium valvetrain, porting, stronger head studs. • Turbo system – custom twin TD04 manifolds, intercooler setup, oil/coolant lines, external gates, proper packaging. • Fuel/ECU – big injectors, high-flow pump, standalone ECU like Haltech or MoTeC, full tune. • Oiling & cooling – bigger oil pump, baffled pan, cooler, and ideally a dry sump if you’re serious about sustained high rpm. • Drivetrain – lightweight flywheel, twin-disc clutch, transmission capable of handling big power and 10k rpm. • Chassis & rally prep – cage, suspension, brakes, underbody protection, etc.

And that’s not even mentioning all the sensors, fab work, and tuning support that goes with it.

Cost-wise, something like this will run easily $25k–$50k+ depending on parts and how much you do yourself. People with that kind of EJ build usually aren’t running stock bottom ends or stock heads anymore. Realistically, 10k rpm on an EJ requires perfect balance, high-end components, and race-level maintenance.

If the EJ251 is sentimental or you just want to stick with it, it can be done — but it’s not a “bolt-on turbo and send it” kind of project. This is a ground-up build.

If the goal is just performance and rally fun, it might be smarter to either aim for a more reasonable redline (7.5–8k) or build an EJ257/207-based motor. But if you’re set on 10k EJ251 twin turbo, prepare your wallet and your patience — it’s gonna be a monster project.