Choosing the Right Z Car for an RB20DET Swap

The Nissan RB20DET is a popular engine swap choice for the Nissan Z car lineage, particularly the S30 (240Z, 260Z, 280Z) and S130 (280ZX) chassis. The RB20DET offers a high-revving, turbocharged inline-six that dramatically improves horsepower and torque over the original L-series or even the later VG engines. However, the swap complexity varies significantly by chassis. The S30 chassis requires more fabrication for engine mounts, transmission crossmembers, and tunnel modifications, while the S130 has slightly more room but still needs custom mounts. Z31 (300ZX) and Z32 (300ZX) swaps are also possible but involve more electronics and integration with modern chassis systems.

Before starting, verify the condition of your donor engine. A JDM RB20DET (typically from an R32 Skyline, Laurel, or Cefiro) should have low mileage, good compression, and minimal smoking. Budget for a complete swap package: engine, transmission (RWD version), wiring harness, ECU (or standalone), intercooler, and all accessories. ZCar.com forums have dedicated swap threads that can help you choose the best starting point.

Tools and Materials: Build Your Arsenal

A thorough tool list ensures you don’t interrupt the job mid-way.

  • Engine hoist (2-ton minimum) and load leveler
  • Metric socket set (10mm to 24mm) with extensions and universal joints
  • Torque wrench (ft-lb and inch-lb ranges)
  • Engine stand for pre-swap preparation
  • Cutoff tool or plasma cutter for modifying transmission tunnel
  • Welder (MIG) for custom engine and transmission mounts
  • Multimeter and soldering iron for wiring
  • Safety gear: gloves, safety glasses, fire extinguisher
  • Specialty items: RB20DET-specific engine mount brackets, Z car conversion motor mount inserts, and a hydromotive damper puller

Pro tip: Purchase a “swap kit” from vendors like McKinney Motorsports or Techno Toy Tuning. These include pre-fabricated engine mounts, transmission crossmembers, and sometimes wiring harness adapters, saving hours of fabrication.

Engine Preparation: Don’t Drop a Dirty Motor

Prep the RB20DET on a stand before installation. This step prevents failures and simplifies the install.

Timing Belt and Water Pump

Replace the timing belt, tensioner, idler pulleys, and water pump. The RB20DET is an interference engine; a broken belt means bent valves. Use genuine Nissan or Aisin components. Set the cam timing to factory specs using the crank and cam sprocket marks.

Gaskets and Seals

Replace front and rear main seals, valve cover gaskets, and the oil pan gasket. The oil pan often leaks after removal, so use a new Nissan gasket with a thin layer of RTV. Upgrade to a metal head gasket only if you plan for high boost; for stock boost levels, a multi-layer steel (MLS) OEM-style gasket is fine.

Fuel System Modifications

The RB20DET uses a return-style fuel system. Your Z car likely has a return fuel line, but the factory Z pump may be inadequate. Install a Walbro 255 LPH (or equivalent) in-tank or inline pump. Replace fuel hoses with high-pressure EFI-rated lines (6mm or 8mm). Use a fuel pressure regulator (e.g., Aeromotive 13101) set to 43 PSI at idle with vacuum reference.

Cooling System Upgrades

The RB20DET produces more heat than the original L-series. Use a three-core aluminum radiator with dual electric fans (e.g., Mishimoto or Griffin). Install a 160-degree thermostat for cooler operating temps in traffic. Upgrade to a Koyo radiator if your Z has AC and power steering clearance issues. Ensure the fan shroud pulls air effectively through the radiator.

Removing the Old Engine: Step by Step

Disconnect the battery negative terminal. Drain engine oil, coolant, and transmission fluid. Label every connector and hose with tape and marker to avoid confusion later. Remove the hood for clearance. Unbolt the radiator, fan, and any intercooler piping. Disconnect fuel lines, brake booster hose, and wiring harness. Unbolt the exhaust manifold from the downpipe. Remove the driveshaft and disconnect the transmission from the engine. Use a transmission jack to support the gearbox. Unbolt engine mounts and lift the engine out carefully with a hoist and leveler. Keep the old engine for sale or core exchange.

Common mistake: Forgetting to remove the transmission before lifting the engine. In the Z car, it’s easier to drop the transmission from underneath while the engine is lifted out—or remove them as one unit if the tunnel is cut sufficiently. The S30 chassis requires lifting the engine slightly forward to clear the front crossmember.

Fabricating and Installing Engine Mounts

Your Z car needs custom engine mounts to position the RB20DET. Off-the-shelf swap kits exist for S30 and S130, but you may need to weld tabs to the stock L-series crossmember. Use solid polyurethane mounts to minimize engine movement under load and improve throttle response. Position the engine so that the oil pan clears the steering rack and the turbo clears the frame rail. On S30, the stock L-series mounts place the engine far forward; you want the RB20DET set back ~1–2 inches for weight distribution. Measure the angle: the transmission tail shaft should point at the differential input with a 2–3 degree downward slope.

Transmission and Drivetrain

The RB20DET typically comes with a FS5W71C or FS5R30A transmission (depending on the donor). The latter is stronger and better for torque. The transmission tunnel in the Z car needs to be widened or cut for clearance. Use an RB20DET-specific transmission mount bracket that bolts to your Z’s transmission tunnel. Pair the transmission with a Nissan R200 differential from a later ZX or 240SX with an R200 diff. You’ll need custom driveshaft: measure the distance from transmission yoke to differential flange and have a shop shorten an S30 driveshaft or build a new one using DOM tubing and 1310/1330 U-joints. Upgrade to a clutch kit rated for 300 hp (e.g., ACT or Exedy stage 1) to handle the RB20DET’s torque.

Wiring Harness and ECU

The RB20DET’s original wiring harness can be reworked, but it’s prone to age-related failures. Options:

  • Modify the factory harness: Strip it down, remove unnecessary circuits, and extend the engine-side connectors to reach the battery, fuse block, and ECU. Use a wiring diagram from 240SX One as the RB20DET harness is similar.
  • Standalone ECU: Haltech, Link, or AEM ECUs allow you to bypass the factory ECU and eliminate the MAF sensor (switch to MAP sensor). This simplifies wiring and permits easy tuning. You’ll need a wiring harness adapter (e.g., from Wiring Specialties) that plugs into the RB20DET’s engine connectors and provides a simplified pigtail for your Z car.

Regardless, install a fresh 12V feed from the battery with a 60A fuse for the ECU and fuel pump. Ground the engine to the chassis with a 4-gauge cable. Never trust 30-year-old wires.

Fuel System Upgrades (Detailed)

Beyond the pump and lines, install a high-pressure fuel filter (inline, 10-micron). The Z car’s original filter location may be re-used but upgrade to a spin-on EFI filter (e.g., WIX 33481). Use AN6 fittings for the supply line and AN4 for the return to prevent restriction. If the Z car has a mechanical fuel pump originally, block it off and route the feed line from the tank.

Exhaust System

Fabricate a downpipe from the RB20DET’s single-scroll turbo (the stock cast elbow). Use 2.5-inch diameter stainless steel tubing with a flex joint to prevent cracking. Pair it with a high-flow catalytic converter if emissions apply, or a test pipe. A 3-inch exhaust from the downpipe back will free up ~15 hp. The Z car’s rear suspension may require a mandrel-bent custom route to avoid the torque tube or control arms. Use a DynoMax or Magnaflow muffler for a deep note.

Cooling System (Additional Details)

Install a coolant overflow tank that matches the Z’s factory style or use a universal aluminum unit. The RB20DET’s water outlet faces the front (driver’s side on RWD); ensure the upper radiator hose clears the intake manifold. Use a thermostatic fan switch in the radiator (e.g., 82°C on, 75°C off) for reliability. Bleed the cooling system thoroughly after filling to avoid air pockets. For S30, you may need to use a Z32 electric fan setup for better airflow with AC.

First Start and Tuning

Before attempting to start, triple-check: all sensors plugged, fuel lines under pressure (listen for leaks), oil filled to proper level, coolant bled, and timing set. Connect a tachometer to the ECU output. Crank for 10 seconds with the fuel pump fuse removed to build oil pressure. Then reinsert the fuse, start the engine. It may run roughly initially if the MAF sensor is dirty or the ECU has learned wrong idle. Allow it to warm up to operating temperature. Check for exhaust leaks, oil leaks, and coolant leaks. Use a scan tool (if using stock ECU) to read trouble codes. With a standalone, perform a basic MAP sensor calibration and idle tuning.

Break-In Procedure

If you refreshed the engine with new rings or bearings, follow a proper break-in schedule: drive at varying loads (not constant speed) for the first 500 miles, avoid full throttle above 3,000 rpm for the first 200 miles, then gradually increase. Change oil and filter after break-in using conventional 10W-40, then switch to synthetic. The RB20DET benefits from a high-zinc oil (e.g., Valvoline VR1) for the flat tappet camshafts.

Common Issues and Troubleshooting

  • Engine won’t crank: Check battery connections, main relay, starter signal wire. RB20DET starters are sensitive to grounding.
  • No start / no spark: Verify ECU power and ground, check ignition module (power transistor). Use a test light.
  • Overheating: Air pockets, collapsed hose, faulty thermostat, or wrong radiator cap. Re-bleed and replace with 13 psi cap.
  • Rough idle: Vacuum leak, dirty MAF sensor (clean with MAF cleaner), or adjust idle air control screw.
  • Turbo lag: Check for boost leaks on intercooler piping. The stock RB20DET turbo (T3/T25) is small and spools quickly; if it’s laggy, inspect wastegate actuator.

Performance Tuning Tips

Once the swap is running well, consider a boost controller (manual or electronic) to raise boost from 7 to 12 PSI with stock injectors and fuel pump. Upgrade injectors to 440cc (or 550cc for more headroom) and tune with a standalone. A front-mount intercooler reduces intake temperatures dramatically. For the ultimate street RB20DET Z, install a GT2860RS turbo and a metal head gasket to safely run 18 PSI. RB-DET.com has detailed upgrade guides.

Conclusion

Installing an RB20DET in your Z car is a challenging but immensely rewarding project that modernizes the driving experience while retaining the iconic chassis. Careful planning, quality parts, and patience are the keys to success. By following this detailed guide, you’ll avoid common pitfalls and create a reliable, powerful Z car that turns heads and performs on the road. Remember: every swap is a little different—document your progress, learn from community forums, and enjoy the build.