Why the SR20DET Swap Reigns Supreme for the S13 240SX

Dropping an SR20DET into your S13 240SX is one of the most rewarding upgrades you can tackle. That old KA24E or KA24DE – while reliable – leaves you longing for turbocharged power, sharper throttle response, and a legitimate aftermarket ecosystem. The SR20DET swap transforms a decent daily driver into a seriously fun street machine or weekend track weapon. With a budget around $3,500, you can execute a swap that’s both potent and dependable.

This guide walks you through the entire process: picking the right engine, choosing supporting parts, pulling the old mill, fitting the new one, and buttoning everything up. Let’s get your car breathing fire again.

Parts and Tools You’ll Need

Success starts with a well-stocked parts list. You can buy a complete front clip (engine, transmission, wiring harness, ECU, intercooler, and sometimes even axles) for around $1,500–$2,000. Alternatively, source individual components. Below is a comprehensive checklist.

Engine and Drivetrain

  • SR20DET long block – Prefer a blacktop (higher compression, better cams) or a redtop (more popular, easier to find). Ensure it comes with the turbo, intake manifold, and exhaust manifold.
  • SR20DET 5-speed transmission – The S13 redtop/blacktop trans is a direct fit. You’ll also need the clutch fork, release bearing, and pilot bushing.
  • Engine mounts – Nismo or aftermarket polyurethane mounts for a secure fit. OEM rubber works, but poly reduces engine movement.
  • Flywheel and clutch – A lightweight flywheel (e.g., ACT or Fidanza) and a streetable clutch (ACT HD, South Bend) will handle stock-to-moderate power levels.

Fuel System

  • Walbro 255-lph fuel pump – A must for any turbo swap. Drops right into the S13 tank with a $10 installation kit.
  • Fuel pressure regulator – An adjustable unit (such as AEM or Aeromotive) lets you dial in pressure when running bigger injectors.
  • Fuel lines – If your S13’s lines are rusty or you’re upgrading, use high-pressure rubber hose or -6AN braided line.

Cooling System

  • Koyo or Mishimoto aluminum radiator – Thicker core handles the SR’s heat much better than the stock KA radiator.
  • SR20DET-specific radiator hoses – Many kits exist; just verify they match your chassis and engine orientation.
  • Dual electric fans – Slim fans (e.g., SPAL) pull plenty of air through the radiator.

Exhaust

  • SR20DET downpipe – A 3-inch downpipe (from a reputable brand like Megan Racing or ISR) is essential for low-restriction flow.
  • Catback exhaust – If you don’t already have a 3-inch system, plan for a full exhaust. Used KA SR20DET catbacks are common.

Wiring and Electronics

  • SR20DET engine harness – Ideally from the same clip as your engine. Important: The S13 SR20DET chassis side (body harness) differs from the KA harness. You’ll need to merge or swap the under-dash fusebox and related connectors.
  • ECU – OEM SR20DET ECU is fine for a basic swap. For tuning, a Nistune board or a standalone like Haltech Elite 750 is worth the investment.
  • Mafs and air filter – The stock SR MAF works up to around 300 hp. A Z32 MAF is a common upgrade for higher flow.

Miscellaneous

  • Intercooler and piping – A front-mount intercooler (24x12x3 is typical) with aluminum piping and silicone couplers.
  • Engine hoist and load leveler – Essential for safe lifting.
  • Sockets, wrenches, breaker bar, torque wrench, and jacks/stands.

Budget Breakdown ($3,500 Target)

Here’s a realistic budget allocation. Prices vary, but this is a solid ballpark.

  • Engine/Transmission front clip – $1,800 (shipped).
  • Clutch and flywheel – $300.
  • Fuel pump – $100.
  • Radiator and fans – $250 (used deals).
  • Intercooler kit – $200 (eBay kit works fine; just upgrade couplers).
  • Exhaust downpipe – $100.
  • Wiring fix parts – $100 (connectors, wire, tape).
  • Engine mounts – $80.
  • Fluids, gaskets, filters – $150.
  • Miscellaneous (tools, bolts, hoses) – $120.
  • Total – ~$3,200, leaving margin for shipping surprises.

Preparation: Getting the S13 Ready

Before touching the old engine, spend a day prepping the car. Thorough preparation prevents half-assed results.

  • Disconnect the battery – negative terminal first.
  • Drain all fluids – oil, coolant, power steering fluid. Dispose properly.
  • Remove the hood – it gives you easy access and prevents accidental scratching.
  • Bag and label every connector – the wiring will thank you.
  • Clean the engine bay – pressure wash to remove grease and dirt. You’ll see things you never noticed.
  • Inspect chassis and replace worn bushings – if your suspension is tired, now is the perfect time to install polyurethane bushings or new control arms.

Engine Removal: The KA Comes Out

You’re likely pulling the original KA24E (single-cam) or KA24DE (dual-cam). The process is similar.

  1. Disconnect everything attached to the engine: intake tube, coolant hoses, heater hoses, power steering lines, AC compressor (if equipped), alternator wires, starter wires, and the engine harness main plug.
  2. Remove the radiator and fans – gives clearance.
  3. Drain the transmission if you’re keeping it for the swap (you’re not, but still).
  4. Unbolt the driveshaft – mark the differential flange orientation so reinstallation is vibration-free.
  5. Support the transmission with a jack, then unbolt the transmission crossmember.
  6. Unbolt the engine mounts – the engine will drop a bit.
  7. Attach the hoist to the engine eyelets – front eye on intake manifold side, rear eye on exhaust side.
  8. Lift slightly while wiggling the engine/transmission assembly.
  9. Slide the engine forward and up – be careful not to hit the brake master cylinder or firewall.

Once the old powertrain is out, set it aside. You can sell the KA and transmission to recoup $300–$500.

Installing the SR20DET: The Heart Transplant

Now the fun begins. The SR20DET is a physically smaller and lighter engine than the KA, but several details require attention.

Mount the Engine

  1. Bolt the SR20DET engine mounts – use new OEM or poly mounts. The engine bracket that bolts to the block must be the correct side (left/right).
  2. Attach the transmission to the engine – install the new pilot bushing in the crank flange, then slide the transmission onto the block. Torque bellhousing bolts to factory spec (~35 ft-lbs).
  3. Lower the engine into the bay with a load leveler. Watch the oil pan clearance – an aftermarket pan might contact the crossmember. Factory SR20DET pans clear the S13 crossmember without issues.
  4. Align engine mounts with the subframe – bolt them in loosely, then tighten after bellhousing and transmission mount are aligned.

Transmission Crossmember

You’ll need an S13 SR20DET transmission crossmember – these are different from the KA transmission crossmember. The SR trans sits slightly different. Buy one from a reputable seller or modify yours if you’re handy with a grinder and welder.

Driveshaft

If you’re using the SR20DET transmission, the SR driveshaft is necessary because the SR output flange size differs from the KA. You can also have your KA driveshaft shortened and rebalanced to match the SR transmission. Many used S13 SR driveshafts sell for around $80.

Connecting Components

Fuel System

Install the Walbro 255 pump in the tank. Don't skip the install kit – it includes the correct strainer and wiring adapter. Run new fuel line to the engine bay if possible, or at least replace old rubber sections. Connect the fuel feed line to the SR’s fuel rail.

Intercooler and Piping

Mount the intercooler using brackets that sandwich the core (many eBay kits come with them). Cut or remove the bumper reinforcement to make room. Route the hot-side pipe from the turbo outlet to the intercooler, and the cold-side to the throttle body. Secure with T-bolt clamps to prevent boost leaks.

Cooling System

Install the radiator, fans, and hoses. The SR20DET water outlet points toward the driver side – you’ll need a S13 SR-specific upper radiator hose (or use a universal hose with a bend). Fill with 50/50 coolant.

Exhaust

Bolt on the downpipe (make sure it clears the steering shaft – some downpipes need a slight dent). Connect the rest of the exhaust from there.

Wiring and ECU: The Brain of the Operation

This is the most intimidating part, but it’s manageable if you’re methodical. The S13 SR20DET uses a different body-side connector than the KA. You have two options:

  1. Buy a pre-made conversion harness – companies like Wiring Specialties or Chase Bays sell plug-and-play harnesses for around $350–$500. Money well spent.
  2. Piggyback or splice yourself – cut the KA body-side connectors and solder them to the SR engine harness. You’ll need diagrams (the FSM is your friend). Pinouts are available at Zilvia.net forums.

Regardless of method, you must connect:

  • Constant 12V, ignition 12V, and starter signal.
  • Grounds from the engine to the chassis.
  • Check engine light, tachometer, speed sensor.
  • AFM (MAF) – mount it on the cold-side intake pipe.

For the ECU, an OEM SR20DET ECU works well for stock boost. If you plan to increase power, consider a Nistune board (you can tune via software) or a standalone like Haltech Elite 750. Proper tuning will unlock the full potential and keep the engine safe.

Start-Up and Testing

  1. Double-check all fluid levels – oil, coolant, power steering, brake fluid.
  2. Prime the fuel pump – cycle the key on and off a few times to pressurize the system.
  3. Crank the engine without ignition for 10 seconds to build oil pressure. Watch the oil pressure gauge.
  4. Connect the ignition and start. It should fire quickly. If not, check spark and fuel.
  5. Let it idle and listen for unusual noises. Check for coolant and fuel leaks.
  6. Check for DTCs – an SR ECU will flash the check engine light if something’s wrong. Common issues: MAF unplugged, TPS misadjusted.
  7. Test drive – once the engine reaches operating temperature, take it easy for the first 20 minutes. Avoid full boost until you’ve done a few heat cycles and verified the tune.

Common Gotchas

  • Steering shaft clearance – the SR manifold sits close. If it rubs, adjust the engine position slightly or dent the downpipe lightly.
  • Speedometer – the S13’s mechanical speedometer cable fits the SR transmission with an adapter. Or convert to GPS speedo.
  • Radiator fan wiring – wire the electric fans through a thermostatic switch or manual override.

Performance Tuning and Future Upgrades

Once the swap is running, you’ll quickly crave more power. Common bolt-ons include:

  • Boost controller (manual or electronic) – raise boost from 7 psi to ~12 psi on stock internals safely.
  • 3-inch full exhaust – mandatory for flow.
  • Bigger injectors (550cc or 740cc) and a Z32 MAF to support 300+ whp.
  • Turbo upgrade – a GT2871R or GTX2867R is a direct fit on the stock manifold with a different downpipe.

For serious builds, internal engine upgrades (forged rods, pistons, head studs) allow 400+ hp. The SR20DET’s aftermarket support is massive – you’ll find parts at Enjuku Racing, Godspeed Project, and many others.

Conclusion: Your S13 Reborn

Swapping an SR20DET into your S13 240SX is a milestone project. It’s not impossibly hard – just methodical. Stick to a budget, buy a complete front clip to minimize missing parts, and don’t rush the wiring. In a long weekend (and a few evening sessions) you can go from a tired KA to a screaming turbo Nissan.

The first time you hear that SR idle with that iconic lope, you’ll know every hour under the hood was worth it. Get assembling, and feel that boost hit!

Community tip: Join the Club S12 and Nissanity for build threads and troubleshooting. You’re not alone in this journey.