The Nissan 240SX remains one of the most popular platforms for aftermarket performance builds, and swapping in or turbocharging the RB20DET is a well-trodden path for enthusiasts seeking a unique balance of inline-six smoothness and big power potential. While the RB20DET offers a strong foundation from the factory, adding or upgrading a turbocharger can transform the car’s character entirely. This guide provides a detailed breakdown of the power gains, costs, supporting modifications, and real-world considerations for turbocharging an RB20DET in a 240SX.

RB20DET Engine Overview and Factory Capabilities

The RB20DET is a 2.0-liter inline-six turbocharged engine produced by Nissan from the late 1980s through the early 1990s. It was originally found in models such as the R32 Skyline, Laurel, and Cefiro. In factory trim, the engine produces approximately 200–215 horsepower and 195 lb-ft of torque, depending on the exact variant (single-cam or dual-cam). The engine features an iron block and an aluminum cylinder head, providing a strong base for forced induction upgrades.

Key Specifications

  • Displacement: 1,998 cc
  • Configuration: Inline-six, DOHC 24-valve
  • Factory compression ratio: 8.5:1
  • Factory turbo: Small T25-type (typically 0.48 A/R turbine housing)
  • Redline: 7,200 rpm

The factory turbocharger is designed for quick spool, but it runs out of breath at higher RPM. For serious power gains, upgrading the turbo and supporting systems is essential.

Turbocharger Selection for the RB20DET

Choosing the right turbocharger depends on your power goals, budget, and driving style. The RB20DET responds well to a range of turbos, from quick-spooling street units to large frame turbos for drag racing.

  • Garrett GT2871R (0.64 A/R): Ideal for 300–350 whp. Spools quickly and retains excellent driveability.
  • Garrett GT3076R (0.82 A/R): Good for 350–450 whp. A classic balance of response and top-end power.
  • Precision 5858 Gen2: Modern ball-bearing turbo capable of 400–500 whp on the RB20 with proper fuel and tuning.
  • BorgWarner S200SX (57mm): Budget-friendly option that can support 350+ whp with excellent efficiency.

For most street builds targeting 300–400 whp, a GT3076R or equivalent will provide a broad powerband. Spool time is still reasonable due to the 2.0L displacement, though slightly laggier than factory.

Power Gains at Different Boost Levels

Power output scales with boost pressure, but limitations like fuel system capacity, intercooler efficiency, and engine internals must be considered. The RB20DET’s stock internals (forged rods and cast pistons) can handle around 350–400 whp reliably with proper tuning.

Boost Level (psi) Estimated Wheel Horsepower Required Turbo
10 ~260–280 whp Stock T25 or small upgrade
14 ~300–330 whp GT2871R
18 ~350–380 whp GT3076R
22–24 ~420–450 whp GT3076R or Precision 5858

Note: These numbers assume a healthy engine, proper fuel system, and professional tuning. Higher boost levels may require forged pistons and rods for long-term durability.

Cost Breakdown for a Turbocharging Project

Costs vary widely based on parts quality, DIY vs. shop labor, and whether you start from a stock RB20DET or one already swapped into the 240SX. Below is a realistic budget for a 300–400 whp build.

Parts and Labor Estimates

  • Turbocharger kit (manifold, downpipe, turbo, wastegate): $1,500 – $3,500
  • Intercooler and piping: $300 – $800
  • Fuel system (injectors, pump, lines): $500 – $1,200
  • Engine management (standalone ECU or piggyback): $600 – $1,500
  • Exhaust system (3-inch cat-back or turbo-back): $400 – $1,000
  • Tuning (dyno tuning session): $400 – $1,000
  • Miscellaneous (gaskets, oil lines, couplers, clamps): $150 – $400
  • Labor (if not DIY): $800 – $2,000

Total estimated range: $3,650 – $11,400. A smart DIY builder with used parts can hit the lower end; a turnkey build with all-new parts and shop labor lands near the upper end.

Supporting Modifications That Make or Break the Build

Throwing a big turbo on a stock engine is a surefire way to detonation and blown head gaskets. The following supporting modifications are critical for reliability and performance.

Fuel System Upgrades

The stock RB20DET fuel pump and injectors (270cc) are insufficient beyond 250 whp. Upgrade to at least 550cc injectors and a Walbro 255 lph pump for 300 whp. For 400+ whp, use 750cc or 1000cc injectors and a surge tank setup.

Intercooler and Charge Piping

A front-mount intercooler (FMIC) with 2.5-inch piping keeps intake air temperatures manageable and reduces the risk of detonation. Avoid thin-core universal units; a core around 24x12x3 inches with cast end tanks works well.

Engine Management

Factory ECU cannot compensate for larger injectors, altered MAF voltage, or increased boost. A standalone ECU like the AEM EMS Series 2, Haltech Elite 750, or Link G4+ provides full control. If budget is tight, a Nistune board or an SAFC Neo can work for mild builds, but standalone is strongly recommended for safety and power output.

Exhaust System

A 3-inch turbo-back exhaust with a high-flow catalytic converter (or test pipe) minimizes backpressure. Avoid restrictive mufflers; a straight-through design keeps spool quick.

Cooling and Oil System

Upgrade to a larger aluminum radiator (e.g., Koyorad or Mishimoto) and an oil cooler. The RB20DET generates significant heat under boost, and oil temperatures above 250°F can degrade lubrication quickly.

Tuning Process and Dyno Tuning Requirements

Professional dyno tuning is the single most important step after assembling the hardware. A competent tuner will adjust fuel maps, ignition timing, boost control, and knock protection. Expect two to four hours of dyno time for a basic street tune, and more for full-throttle optimization.

Avoid mail-order tunes or base maps; every engine and vehicle combination is unique. A poor tune can destroy an engine in seconds under boost.

Reliability Considerations and Common Pitfalls

The RB20DET is sturdy, but pushing it beyond 400 whp on stock internals often leads to rod failure. The stock connecting rods are forged but weak in the beam area. Many enthusiasts install CP pistons and Carrillo or Eagle rods for 400+ whp builds.

  • Head gasket: Cometic MLS head gasket and ARP head studs are mandatory above 18 psi.
  • Oil starvation: The RB20DET can starve the turbo under hard cornering. Install an oil restrictor in the turbo feed line and consider an accusump.
  • Ignition: Stock coils can misfire at higher boost. Upgrade to R35 GT-R coils or aftermarket CDI ignition (e.g., MSD or AEM).
  • Cooling: Monitor coolant temperatures with an aftermarket gauge; the stock gauge is too vague.

Comparison with Alternative Engine Swaps

Many 240SX owners consider swapping in an SR20DET or an RB25DET instead of heavily modifying the RB20. Here is a short comparison.

  • RB20DET turbo build (300–350 whp): Cost: ~$5,000–$8,000. Unique sound, good torque curve. Limited aftermarket support compared to SR.
  • SR20DET swap (built motor, 350–400 whp): Cost: ~$6,000–$10,000. Lighter engine, huge aftermarket, revs higher. Less torque than RB20.
  • RB25DET swap (stock turbo, 300 whp): Cost: ~$4,000–$7,000. More displacement, easy 300 whp with stock internals. Heavier, longer engine causing oil pan clearance issues in 240SX.

For a 240SX that already has an RB20, turbocharging it is often the most cost-effective path rather than swapping to another engine. However, if you are starting from a stock KA24DE, an RB25DET swap may offer better value per horsepower.

Installation Steps Overview

While a full installation guide is beyond this article’s scope, here is a high-level sequence for a DIY install.

  1. Remove stock turbo and exhaust manifold. A hot wrench or penetrating oil helps with rusted bolts.
  2. Mount new turbo manifold (preferably a top-mount or bottom-mount design with T3 or T4 flanges). Use new gaskets.
  3. Install turbocharger with oil feed and drain lines. Ensure the drain line has a downward slope for gravity return to the oil pan.
  4. Mount intercooler and charge piping. Routed away from heat sources.
  5. Upgrade fuel system – swap pump, install injectors, check fuel pressure.
  6. Install standalone ECU and wire in harness adapters. Use a pinout diagram specific to the 240SX chassis.
  7. Run new intake and blow-off valve. Plumb the BOV back into the intake if you need to bypass MAF sensors (some ECUs eliminate MAF).
  8. Setup boost control – manual boost controller for simplicity, or electronic boost controller for adjustable boost on the fly.
  9. Final checks: Verify no oil leaks, coolant leaks, or loose connections. Test fuel pressure.
  10. Dyno tune – do not exceed 5 psi until tuned.

Real-World Driving Impressions and Streetability

A well-tuned RB20DET with a GT3076R and 350 whp delivers a thrilling driving experience. The power comes on strongly around 3,500 RPM and pulls hard to 7,000 RPM. The engine’s smooth inline-six character paired with a proper 240SX chassis provides balanced handling. However, the weight of the RB20 compared to an SR20 does affect front-end grip; consider stiffer springs and adjustable coilovers to compensate.

Daily driving is feasible with a mild turbo setup (GT2871R, 300 whp). Fuel economy will be around 18–22 MPG on highway with light throttle, but severely drops under boost. Idle and part-throttle behaviors are improved with stand-alone ECUs.

External Resources for Further Reading

Final Considerations

Turbocharging an RB20DET in a 240SX is a rewarding project that delivers a potent combination of linear power and distinctive engine note. The key to a successful build lies in budgeting for proper supporting mods, investing in professional tuning, and understanding the limits of the stock internals. With a clear plan and realistic expectations, you can create a turbocharged 240SX that is both exhilarating on the backroads and reliable at the track.