Why Swap an RB26DETT Into a 240SX?

The Nissan 240SX (S13, S14, or S15 chassis) is a lightweight rear-wheel-drive platform that responds incredibly well to a high-horsepower engine swap. The RB26DETT, sourced from the legendary Nissan Skyline GT-R (R32, R33, R34), is a 2.6-liter twin-turbo inline-six that offers a robust iron block, a forged crank, and a factory-rated 276 hp (though actual output is often higher). Swapping this engine into a 240SX transforms the car into a serious performance machine capable of 400–600 hp on stock internals with a proper tune, or well over 1,000 hp with built components. This guide covers the entire process from sourcing the engine to extracting peak performance on the dyno.

Understanding the RB26DETT Engine

Before diving into the swap, it’s important to know what you’re working with. The RB26DETT features a cast-iron cylinder block, aluminum cylinder head with 24 valves, dual overhead cams, and two ceramic-turbine turbochargers. The factory ECU (Engine Control Unit) is sophisticated for its time, but many swappers opt for a standalone ECU for better tunability. The engine’s strengths are its torque curve and ability to handle significant boost. Weaknesses include the fragile stock bottom end on early R32 engines (pre-1993) and the poorly designed oil pan baffling that can cause oil starvation during high-G cornering.

RB26 Variants and What to Look For

Not all RB26DETT engines are equal. The R32 version (1989–1994) uses a smaller oil pump and weaker rods; the R33 (1995–1998) and R34 (1999–2002) versions have improved oil pumps, stronger rods, and better turbos. For the 240SX swap, an R33 or R34 engine is preferable, but an R32 can be built to be reliable. Always check the engine code stamped on the block (e.g., RB26-XXXX). Avoid engines with evidence of rod knock, high mileage without service history, or missing critical components like the turbochargers and intercooler.

Step 1: Purchasing the RB26DETT Engine

Finding a good core is the first hurdle. Start by looking at reputable importers like JDM Engine Depot or Japan Star Imports. Salvage yards specializing in Skyline parts also carry RB26s. When evaluating a potential purchase:

  • Ask for a compression test (should be 150–170 psi across all six cylinders, with no more than 10% variance).
  • Request a leak-down test to verify ring and valve seal.
  • Verify the engine comes with the original turbochargers, intake manifold, exhaust manifold, wiring harness, and ECU.
  • Check the oil for metal shavings (indicates bearing wear).
  • Look at the spark plugs – even color indicates good combustion; oil-fouled plugs suggest ring or valve guide wear.
  • Inspect the serpentine belt and accessories (alternator, power steering pump) for condition.

Step 2: Gathering Necessary Parts and Tools

A successful RB26 swap requires more than just the engine. You’ll need a comprehensive parts list. Many aftermarket companies sell swap kits that simplify the process.

Mandatory Components

  • RB26DETT Engine – complete with turbos, manifolds, and accessories.
  • Transmission – the RB25DET (from R33 GTST) is a popular, cheaper option that bolts up with minor modification. The factory RB26DETT transmission (from a GT-R) is stronger but rarer and more expensive. Both require a custom driveshaft.
  • Engine Mounts – aftermarket companies like McKinney Motorsports make bolt-in mounts for the 240SX chassis.
  • Wiring Harness – you can modify the stock RB26 harness or buy a plug-and-play harness from WireWorx. Expect to pay $500–$1,000.
  • ECU – a standalone like the Haltech Elite 2500, Link G4+, or Motec M130 is recommended for tuning flexibility. Alternatively, use the factory ECU with a Nistune or RomEtor board for reflashing.
  • Intercooler – the factory Skyline intercooler is small. Upgrade to a front-mount unit that fits the 240SX (core size ~600x300x76mm).
  • Fuel System – Walbro 450lph fuel pump, Bosch 1000cc injectors, and an adjustable fuel pressure regulator.
  • Cooling System – Koyo or Mishimoto radiator designed for the 240SX with an RB swap. A set of SPAL electric fans.
  • Exhaust – 3-inch downpipe and full exhaust from the turbos back. A high-flow catalytic converter (or test pipe).
  • Clutch – a heavy-duty clutch (Exedy, ACT, or South Bend) rated for your target torque.
  • Driveshaft – a custom steel or aluminum driveshaft from a shop that knows RB swap lengths (typically around 47 inches for S13 with RB25 trans).

Step 3: Preparing the 240SX Chassis

Preparation makes the install smoother. Park the car on jack stands, drain all fluids, and remove the battery.

Removing the Stock Engine and Transmission

Disconnect everything from the KA24DE or SR20DET (whichever engine you’re replacing). Label all connectors. Remove the radiator, radiator support (for clearance), wiring harness, and exhaust. Unbolt the transmission crossmember. With a hoist, lift the engine/transmission out of the bay. Take care not to damage the A/C lines if you plan to keep A/C (many swappers delete it, but a compact A/C compressor can be installed for a sleeper build).

Engine Bay Preparation

Clean the engine bay thoroughly with degreaser and a pressure washer. Sand down any rust and apply primer/paint. Install the McKinney or ISR Performance engine mounts – they usually require grinding off the original KA mounts on the subframe and welding on new mounts (or using bolt-on brackets). Also, you will need to move the transmission crossmember rearward about 3 inches for the RB transmission. Drill new holes or slot the existing ones.

Modifying the Transmission Tunnel

The RB25 or RB26 transmission is longer than the 240SX unit, so you will likely need to cut and widen the transmission tunnel. Use a hammer and dolly to create clearance, or weld in a transmission tunnel kit. This step is critical to prevent the tail housing from hitting the chassis and to allow the shifter to align properly.

Step 4: Installing the RB26DETT Engine

With the bay prepped, it’s time to drop the engine in.

Engine and Transmission Assembly

Bolt the transmission to the engine using the correct flywheel and clutch. For an RB25 transmission, you need the RB25 bellhousing and clutch fork. Use a new pilot bearing and throw-out bearing. Tighten the flywheel to 105 ft-lbs and the pressure plate to 20 ft-lbs (check your clutch manufacturer specs). Lubricate the input shaft splines lightly.

Lowering the Engine

Attach the chains to the lifting hooks on the engine (there are two at the front and rear). Slowly lower the assembly into the bay, tilting it to clear the radiator support. Align the engine mounts with the brackets on the subframe. Once in place, torque the mount bolts to 35 ft-lbs. Then, install the transmission crossmember and bolt it to the transmission tail housing and chassis.

Connecting Ancillaries

  • Install the intercooler and pipe routing before the radiator goes in.
  • Connect the power steering lines (often you reuse 240SX power steering pump and lines, but you may need custom hoses).
  • Attach the alternator and tension the belt.
  • Install the A/C compressor if keeping it.
  • Route the wiring harness from the engine to the cabin (through the firewall grommet).

Step 5: Wiring and ECU Setup

Wiring is the most intimidating part of the swap, but it’s manageable with a plan. Standalone ECUs come with detailed instructions, and many supplier harnesses are largely plug-and-play. Still, expect to do some splicing.

Wiring Harness Integration

If using a custom harness from WireWorx or similar, it will have connectors for the RB26 engine sensors, injectors, ignition coils, and idle air control. You’ll need to connect power (constant 12V, switched ignition +12V, ground), and connect to the chassis harness for gauges, tachometer, and alternator warning light. Common pitfalls:

  • Use a relay and fuse block for the fuel pump, ECU power, and fans. Don’t overload the original 240SX wiring.
  • If you keep the factory ECU, you must wire the ignition trigger from the 240SX body harness (black/white wire at the ignition switch) to the ECU pin that triggers the main relay.
  • The tachometer signal must be converted for the RB26’s trigger pattern. Many standalone ECUs can output a clean tach signal, or you can buy a tachometer adapter (e.g., from Dabstronics).

ECU Configuration Basics

With a standalone ECU, you’ll need to configure basic settings before the first start: injector size, fuel type, number of cylinders, firing order (1-5-3-6-2-4), and ignition timing. Most standalone ECUs have base maps for the RB26, but you must adjust them for your specific fuel system and boost level. Never fire the engine without a tune – you risk detonation and engine damage.

Step 6: Cooling and Fuel System Upgrades

Cooling System

The RB26 runs hot in tight engine bays. A Koyo N-flow radiator (2-row, all-aluminum) is essential. You’ll need to relocate the stock overflow bottle, often to the passenger side using a universal reservoir. Use a 1.3 bar radiator cap. Electric fans (2x 12-inch) wired to a temperature switch or manual overide. Consider a GReddy oil cooler kit to keep oil temps down – essential for track use.

Fuel System

High-flow injectors (e.g., 1000cc) require a larger fuel pump. Install a Walbro 450lph in-tank pump (drop-in for the 240SX). If you want more capacity, use a Fuelab or Aeromotive inline pump. Upgrade the fuel lines to -6AN stainless braided hose from the pump to the engine. Use an adjustable fuel pressure regulator set to 43.5 psi base pressure. Test for leaks under pressure before starting.

Step 7: Final Checks and Initial Start

Do a thorough inspection before turning the key.

  • Check oil level (use high-zinc break-in oil like Valvoline VR1).
  • Fill coolant with distilled water and performance antifreeze (70/30 ratio).
  • Prime the fuel system by cycling the pump several times with the ignition on (if using a standalone, you can do a fuel pump test).
  • Turn the engine over by hand with a breaker bar to ensure no mechanical binding.
  • Disconnect the ignition coils and fuel injectors, then crank the engine to build oil pressure – watch the pressure gauge.
  • Reconnect coils and injectors. Have a fire extinguisher nearby.

First Start Procedure

Start the engine with the throttle slightly cracked. It may run rough until the ECU adjusts idle air. Watch for leaks (fuel, oil, coolant). Check exhaust for odd smells or smoke. Once idling, let it reach operating temperature and look for cooling system air pockets – you may need to burp the system. Set base timing with a timing light (usually 15° BTDC on RB26). Now you’re ready for a shakedown.

Step 8: Tuning and Dyno Results

Do NOT attempt to drive aggressively without a professional tune. For a street car, a good target is 400–500 whp on the stock turbos with 18–20 psi, a boost controller, and 93 octane fuel. On bigger turbos (e.g., Garrett GT3076R twins), 600–700 whp is achievable with E85. The dyno session is where you refine air-fuel ratios, ignition timing, and boost curves.

Dyno Session Tips

  • Use a reputable tuner familiar with RB engines and standalone ECUs. Expect to spend $500–$1,000 for tuning.
  • Bring two data logs: one for street drivability (low-load) and one for wide-open throttle.
  • Monitor knock (even with stock internals, detonation can destroy the engine).
  • After tuning, verify fuel pressure and flow. If the dyno graph shows a sudden dip in power, investigate spark blow-out or fuel starvation.

Typical Dyno Results

A well-swapped RB26 240SX on stock R34 turbos will produce around 350–400 hp at the wheels with a good street tune. With cams, head work, and 25 psi, you can see 500+ whp. The torque curve is broad – expect 350+ lb-ft from 3,500 to 6,500 rpm. For example, a common setup (R32 RB26, Garret 2860-5 turbos, 1000cc injectors, Haltech ECU) yields 480 whp and 410 lb-ft on 93 octane. On E85, 550 whp is typical without rebuilding the short block.

Conclusion

The RB26DETT 240SX swap is a demanding but immensely rewarding project. It requires careful parts selection, meticulous wiring, and professional tuning, but the result is a unique, high-performance car that can compete with modern sports cars. Whether you build a daily driver or a time-attack monster, the steps outlined here will help you avoid common mistakes and get the most from your swap. After the dyno, enjoy the experience of driving one of the most iconic engine swaps in car culture.