The Nissan 240SX remains one of the most iconic platforms in the enthusiast community, prized for its light curb weight, near-perfect 50/50 weight distribution, and rear-wheel-drive layout. For owners seeking a significant power upgrade without the complexity of a V8 or the high cost of a full RB26 swap, the RB20DET offers an appealing middle ground. This turbocharged 2.0-liter inline-six, sourced from Japanese-market Skylines and Laurels, bolts in with relative simplicity and transforms the car’s character. In this article, we break down the realistic costs, parts required, and real-world performance gains you can expect from an RB20DET installation into a 240SX.

Overview of the RB20DET Engine

Introduced in the late 1980s, the RB20DET is part of Nissan’s legendary RB engine family. The “RB” designation stands for “Response and Balance,” and the engine lives up to that name. It features a 2.0-liter displacement (78.7 mm bore x 73.7 mm stroke), dual overhead camshafts, 24 valves, and a water-cooled turbocharger. Depending on the specific version (R32 Skyline, Laurel, Cefiro), stock power ranges from 200 to 220 horsepower at the flywheel and around 200 lb-ft of torque.

What makes the RB20DET particularly attractive for the S13 chassis is its narrow inline-six design, which fits between the strut towers without the heavy weight penalty of larger engines like the RB25 or RB26. The engine’s iron block and aluminum head provide a robust foundation, and the factory Garrett/Mitsubishi turbocharger is capable of supporting 300-350 horsepower with basic bolt-ons and a tune. Additionally, the RB20DET retains a mechanical distributor, making it simpler to wire than later coil-on-plug setups—a major advantage for home builders.

Cost Breakdown

Budgeting accurately for an engine swap is critical. Below we break down the major cost categories, including parts that are often overlooked. All prices are in USD and reflect current market trends as of 2025.

1. Engine Purchase

Complete front-clip or half-cut purchases are becoming rarer. Most enthusiasts now buy a standalone long block or short block. Prices vary by condition, mileage, and inclusion of ancillaries.

  • Used stock RB20DET (complete with turbo, manifolds, injectors, harness, ECU): $1,500 – $2,500
  • Low-mileage or JDM-imported engine (top end only): $2,500 – $3,500
  • Rebuilt long block with new bearings, rings, seals: $3,000 – $5,000+
  • Short block (bare block and rotating assembly): $800 – $1,500 (if you already have a good head)

Pro tip: Always compression-test a used engine before purchase. A healthy RB20DET should show 150-170 psi across all six cylinders with less than 10% variance.

2. Mounts, Brackets, and Transmission

The RB20DET uses the same bellhousing pattern as the KA24DE, so your stock transmission (FS5W71C for manual) can be reused with a proper pilot bushing or a conversion spacer. However, many builders opt for a stronger RB25 transmission or a Z32 5-speed.

  • Engine mounts (polyurethane or solid): $150 – $350 (brands like ISR, McKinney, or custom)
  • Transmission crossmember modification or stand-alone mount: $50 – $200
  • Clutch kit (sprung hub, 6-puck for 300+ hp): $250 – $600
  • Driveshaft shortening or custom two-piece: $200 – $450

3. Wiring and Electronics

Wiring is the most intimidating part for many builders, but the RB20DET’s simple engine harness makes it a good first swap. Options range from re-pinning your factory body-side connector to buying a full plug-and-play chassis harness.

  • Stand-alone engine harness (if not included with engine): $300 – $600
  • ECU (stock R32 RB20DET ECU): $200 – $400
  • Upgraded ECU (Nistune, Power FC, or Haltech): $500 – $1,500
  • Wiring specialty service (custom splice): $400 – $800

4. Cooling and Induction

The stock 240SX radiator can work with some creativity, but a thicker aluminum radiator is recommended for hot climates or higher boost levels.

  • Aftermarket aluminum radiator (32mm core): $150 – $350
  • Intercooler kit (front mount with piping): $300 – $800
  • Intake piping and filter (MAF relocate): $50 – $200
  • Electric fans (dual 12-inch): $100 – $250

5. Exhaust and Turbo System

If your RB20DET comes with a stock turbo, it’s adequate for 250-280 hp. For higher goals, a bigger turbo and better manifold are needed.

  • Downpipe and test pipe: $100 – $300
  • Cat-back exhaust (2.5 or 3 inch): $300 – $800
  • Turbo upgrade (e.g., GT2860RS, BorgWarner S200SX): $700 – $1,500
  • Steel exhaust manifold (top-mount for external wastegate): $400 – $1,000

6. Miscellaneous & Hidden Costs

First-time swappers often forget these items:

  • Fuel pump (Walbro 255 lph or equivalent): $80 – $150
  • Fuel pressure regulator (adjustable): $50 – $150
  • Boost controller (manual or electronic): $30 – $300
  • Gauges (boost, oil pressure, coolant temp): $100 – $400
  • Power steering lines (high-pressure hose modification): $30 – $100
  • AC delete or custom AC lines: $50 – $200

Labor and Tools

If you are not doing the swap yourself, professional shops typically charge $1,500 – $3,000 for an RB20DET swap, depending on complexity and whether you supply a complete running engine. For DIY builders, tool costs can add $200 – $500 for engine hoist, engine stand, torque wrench, and specialty sockets (e.g., for RB’s cam gear nuts).

Total Estimated Cost

Adding it all up, a well-rounded RB20DET swap into a 240SX falls within these ranges:

  • Budget DIY (used engine, stock parts, no tuning): $2,500 – $4,000
  • Mid-range (rebuilt engine, upgraded turbo, ECU tuning): $5,000 – $8,000
  • Premium build (fully built long block, stand-alone ECU, big turbo, all new ancillaries): $8,000 – $14,000

Remember that these figures do not include the purchase price of the 240SX itself, nor do they account for potential chassis rust repair or suspension upgrades needed to handle the extra weight (the RB20 is about 50 lbs heavier than a KA24DE).

Performance Gains

Once installed, the RB20DET delivers a dramatic improvement over the stock KA24E or KA24DE.

Stock vs. Tuned Output

  • Stock RB20DET (7-8 psi): 200-220 hp / 200-210 lb-ft at the wheels (roughly 240-260 at crank)
  • Bolt-ons + tune (12-14 psi, intercooler, 3-inch exhaust, boost controller): 280-320 hp / 270-310 lb-ft
  • Turbo upgrade + 16-18 psi + 550cc injectors + stand-alone ECU: 350-400 hp / 320-370 lb-ft
  • Built engine + 20+ psi + E85: 450-500 hp (rare but possible with forged internals)

The torque curve is notably flat and broad compared to a 4-cylinder SR20DET, delivering strong pull from 3,000 RPM to redline. The six-cylinder sound alone is worth the swap for many enthusiasts—a smooth, growling exhaust note that the 240SX never had from the factory.

Driving Characteristics and Handling

The RB20DET adds roughly 50-70 pounds over the front axle compared to a KA24DE. While not negligible, this weight increase is less than an RB25 (+100 lbs) or an LS V8 (+150 lbs). The 240SX’s double-wishbone front suspension can be tuned with stiffer springs and increased caster to maintain turn-in sharpness. Many owners report that the car feels more planted under hard acceleration because the inline-six has a lower center of gravity than a V8.

Throttle response improves dramatically, especially with a lightweight flywheel. The RB20’s factory Garrett T3 or T25 turbo spools quickly (full boost by 3,000 RPM), so there is little lag in daily driving. Combined with a tight gear set, the 240SX becomes a true driver’s car—quick, talkative, and rewarding.

Reliability and Common Issues

The RB20DET is generally reliable if maintained properly, but there are known weak points:

  • Oil pump: RB20 oil pumps can fail at sustained high RPM (7,500+). Upgrade to a Nismo or aftermarket high-volume pump for builds over 350 hp.
  • Valve seals: Aged engines often smoke at startup due to dried-out seals. Replace them during the swap.
  • Ignition system: The factory distributor and igniter module are wear items. Carry a spare or upgrade to a 36-1 trigger wheel with a standalone ECU.
  • Coolant temperature: The engine’s stock thermostat housing is known for rust; upgrade to a billet aluminum version from the 240SX community.

With regular oil changes (5W-30 synthetic) and keeping boost under 15 psi on a stock bottom end, these engines frequently exceed 150,000 miles without major issues.

Alternatives: RB20 vs. SR20 vs. KA-T vs. LS

Every swap has trade-offs. Here is a quick comparison to help you decide if the RB20DET is right for you.

  • SR20DET (2.0L turbo 4-cyl): Lighter by 80 lbs, easier to fit, massive aftermarket. Power ceiling ~400 hp on stock block. Simple wiring, more common parts.
  • KA24DE-T (2.4L turbo 4-cyl): Low cost (~$1,000 for built long block), but requires extensive DIY fabrication for turbo plumbing. Heavy piston design limits RPM.
  • RB20DET: Smooth six-cylinder torque, unique exhaust note, easier swap than RB25, but harder to find parts than SR20.
  • RB25DET (2.5L turbo 6): More power out of the box (250 hp), but heavier and requires oil pan modifications in S13 chassis. More expensive.
  • LS V8 (e.g., 5.3, 6.0): The ultimate power-per-dollar, but adds 150+ lbs, requires significant frame modifications, and changes the car’s balance dramatically.

If you value classic JDM authenticity, inline-six smoothness, and a swap that keeps the 240SX’s nimble feel, the RB20DET is an excellent choice.

Resources and Further Reading

For more in-depth information, check out these community resources:

  • Zilvia.net forums – the largest 240SX community, with dedicated RB swap sections.
  • Import Era – guides and parts sourcing for JDM engines.
  • Enjuku Racing – reliable source for RB-specific mounts, wiring adapters, and tuning components.

Conclusion

Installing an RB20DET into a Nissan 240SX is a rewarding project that balances cost, performance, and character. With a realistic budget of $3,000–$8,000, you can achieve a reliable 280–350 hp setup that transforms the car into a thrilling street machine or weekend track weapon. While the swap demands mechanical aptitude—particularly with wiring—the aftermarket support is strong, and the end result is a vehicle that honors Nissan’s RB legacy. Whether you are a first-time swapper or a seasoned builder, the RB20DET 240SX offers a driving experience that few other combinations can match.