My S13 240SX SR20DET swap from a bare shell – Day 1. No donor car, no prior swap experience. Anyone pulled this off in a single‑bay garage?

Hello, brave souls.
My name is Matt, I’m 34, I have a day job in IT, a wife who tolerates my hobbies, and a 2‑year‑old who thinks every engine part is a toy. I’ve been wrenching on my own cars for about 8 years – I’ve done brakes, suspension, bushings, fluids, and even pulled a Miata engine once just to replace a rear main seal. But I have never done a full engine swap, let alone one that involves changing the entire drivetrain, wiring, and all the ancillaries. Until now.

Last week, I bought a 1989 Nissan 240SX hatchback from a guy in Virginia. It’s a base model, originally with the KA24E (single‑cam), but the engine and trans were long gone when he got it. What I got is a rolling shell: front subframe still in place, suspension arms, steering rack, brakes (stock, seized calipers), a bare interior with a dashboard that’s cracked to hell, a half‑decent body with some surface rust on the rear quarters, and a clean title. The fuel tank is there but looks like a rust farm inside. I paid $1,800 for it. I’ve seen worse.

The SR20DET – a red‑top from a early S13 Silvia – came from a reputable importer in California. They said it’s a low‑mileage JDM engine, compression tested (150–155 psi across all four), includes the factory T25 turbo, intake manifold, exhaust manifold, injectors, ignition coils, and the alternator. No transmission, no harness, no ECU, no intercooler, no piping. I paid $2,400 for the long‑block plus shipping. Then I found a used 5‑speed transmission (the FS5W71C, I think) from a guy on Facebook for $500 – he claimed it came out of a running SR car but I have no proof. So I have a pile of parts that might work together.

My total budget is $8,000 all‑in – including all the missing bits: intercooler, piping, radiator, electric fan, downpipe, exhaust, clutch, flywheel, driveshaft modification, fuel pump, fuel pressure regulator, new brake master cylinder, stainless lines, cooling system hoses, and the dreaded wiring harness adaptation. Oh, and I need to buy a standalone ECU or at least a tuneable daughterboard for the stock SR ECU – haven’t decided yet.

My workshop: a single‑car garage attached to my house. The dimensions: roughly 9 feet wide, 18 feet deep. That means if I have the car in there, I can open the doors barely enough to squeeze out. I have a 3‑ton floor jack, four jack stands, a decent set of metric sockets, combination wrenches, a torque wrench, a Dremel, a drill, an angle grinder, a multimeter, and a soldering iron – but no welding equipment, no press, no engine hoist (yet – I’ll rent one). I have one 110V outlet – no 220V for a welder or compressor. I’ll be using my daily driver (a Subaru Outback) to run to the auto parts store every other day.

So here’s my plan, laid out in phases, with a prayer that I’m not delusional.

Phase 0 – Preparation (Week 1)

• Clean the shell thoroughly, degrease the engine bay, treat rust spots.

• Remove the old fuel tank – I’m replacing it with a used S13 fuel tank from a KA car (found one on OfferUp for $80) and a new Walbro 255lph pump.

• Remove the entire stock wiring harness – it’s mostly cut up anyway – and label every connector I can identify. I’ll need to integrate the SR harness later.

• Get the engine bay painted? Probably not – I’ll just rattle‑can it with Rust‑Oleum because I’m on a budget and I want it protected, not pretty.

Phase 1 – Mechanical assembly (Weeks 2‑6)

• Rent an engine hoist and install the SR with the transmission attached (I’ll need to drop the subframe or raise the car high enough – but I only have jack stands, so maybe I’ll do the subframe drop method that some forum posts describe).

• Bolt up the transmission crossmember – I need the SR‑specific one, which I haven’t bought yet.

• Install the clutch (I’m going with a stock Exedy replacement since I’m only aiming for 250–280 hp).

• Install the driveshaft – the stock KA driveshaft won’t fit because the SR transmission is shorter? Actually I think the S13 SR transmission is the same length as the KA one, but the output spline might differ – I need to check. Worst case, I’ll have a custom driveshaft made by a local shop – that’s about $400.

• Install a new radiator – Koyo or Mishimoto, plus an electric fan – because the SR sits differently.

• Intercooler and piping – front‑mount, with all the couplers and clamps. I’ll need to cut the front bumper support – I have a grinder, so okay.

• Oil cooler – the SR has one from factory, but I might need adapters.

• Exhaust – I need a downpipe that clears the steering column and a full 3” exhaust. I’ll probably buy a used kit and modify it with band clamps because I can’t weld.

Phase 2 – Electronics (Weeks 7‑12) – this is where I’m most terrified

• I have no engine harness. I’m buying a used SR harness from a guy on a forum – it’s a gamble. I also need the ECU (red‑top OEM, or I go for a standalone like a Link or Haltech – but that’s $1,500+). I’m leaning toward a used A’PEXi Power FC with a base map – I can get one for about $600 used, but they’re rare.

• The wiring – merging the SR harness into the S13 body harness for gauges, ignition, starter, alternator, fuel pump relay, etc. I have to figure out the pinouts. I’ve found the SR20 wiring diagrams online, but they’re for RHD cars. The US S13 has different colors and some different connectors for the combination meter. I’m planning to take it slow, label everything, and maybe use a breakout box to test each circuit.

• Also, I need to wire in a wideband O2 sensor and a boost gauge – I’ll use those for tuning.

• I need to bypass the NATS (Nissan Anti‑Theft System) – I think the red‑top SR doesn’t have it, but the body harness might have the immobilizer? My shell is so stripped that I might not have any security system. Still, I need to ensure the fuel pump primes and the starter engages.

Phase 3 – Fuel system (Week 13)

• Replace fuel tank, install new pump, replace all rubber hoses with EFI‑rated lines, add an inline filter.

• Run new fuel feed and return lines – the SR uses a return‑style system, which my car originally had too (KA single‑cam had return). So that might match. But I need to adapt the dampers.

Phase 4 – Brakes, suspension, steering (Week 14‑15)

• Upgrade front brakes to Z32 calipers or at least rebuild the stock ones. I already have a set of used Q45 calipers that I can bolt up with adapters.

• Replace all brake lines with stainless steel.

• Rebuild the steering rack bushings.

• New coilovers – I might keep it on stock struts for now just to roll it, but eventually I need cheap coils.

Phase 5 – Cooling and final assembly (Week 16)

• Fill all fluids, pressure test cooling system, check for leaks.

• Install the exhaust, heat wrap everything.

• Mount the battery – relocate it to the trunk if I have time.

• Get a base tune on the ECU (either from a local shop remote or I’ll trailer it to a tuner).

Phase 6 – First start and shakedown (Week 17‑20)

• Pray. Then crank. If it fires, I’ll do a cam break‑in (for the new valve springs? I’m not replacing them, so I’ll just idle and check oil pressure).

• Break in clutch – 500 miles of gentle driving.

• Then address any leaks, overheating, electrical gremlins.

My specific questions for you veterans:

1. Space constraints: Has anyone done this in a single‑bay garage without a lift? I’m 6’1” and I can barely stand next to the car with the door closed. Is it even feasible to drop the subframe and install the engine from underneath? Or should I just lift the engine in from above with the hood off and get a load leveler? I can’t raise the car more than 18” on stands – is that enough to slide the transmission under?

2. Engine harness – buy pre‑made or make my own? I see companies like Wiring Specialties sell a complete SR S13 harness for $900 – that’s half my budget left. But I’m tempted to make my own from scratch using the KA body harness and a raw SR pigtail – but I have zero experience with automotive wiring diagrams. Is this a fool’s errand? Should I just bite the bullet and buy the plug‑and‑play harness to save my sanity?

3. Driveshaft length: I’ve read that the SR transmission is 20mm longer than the KA trans? Or is it the same? I plan to measure when I get the transmission in, but if I need to shorten my stock driveshaft, local shops charge $150. But I need to know the correct flange pattern – the SR output flange has 6 bolts vs. the KA has 5? I’m confused. Can I just use a KA driveshaft if I swap the front yoke?

4. Clutch hydraulic system: The SR uses a hydraulic throw‑out bearing? Actually it has a push‑type clutch fork. My car has a slave cylinder on the driver’s side. I need to get the correct clutch line – some people use a braided line from the master to the slave, bypassing the dampener. But the SR clutch fork is on the other side? I’ve seen conflicting photos. Can someone with a red‑top S13 tell me exactly which slave cylinder and line to use?

5. Radiator hose routing: The SR has a thermostat housing that points toward the driver’s side (US driver side) or passenger? I’ve seen aftermarket radiator kits that include hoses – but I want to use universal ones with a lower radiator port that’s on the opposite side. What’s the common solution?

6. ECU choice: Should I go with a used Power FC, or a new standalone like a Haltech Elite 750? The Haltech is $1,600 plus harness – that’s almost double. But the Power FC is old and support is fading. I could also run the stock ECU with an Enthalpy tune – they burn chips and mail them to you. That’s only $300. For my power goals (stock T25, maybe 250hp), is the stock ECU with a tune enough? Or will I regret not going standalone when I eventually want to upgrade turbo?

7. Fuel lines: The stock KA return line is 5/16” – is that adequate for 300hp? I think it’s borderline. I’m planning to run new 3/8” feed and return to be safe. But that means dropping the tank and replacing the hard lines – or just running rubber lines inside the cabin? That seems unsafe. What’s the cleanest way without spending $500 on an AN fitting kit?

8. Getting the shifter hole to line up: I know the SR transmission has the shifter further forward than the KA? Or is it the same location? I need to cut the shifter hole or modify the shifter plate. Does anyone have a template for where to cut the trans tunnel for an S13 with an SR? I’ve seen some people use a “shifter relocation” bracket – is that necessary?

9. Cooling – fans and shroud: The SR doesn’t come with a fan clutch – it’s all electric. I need to wire a fan to come on with the ECU or a thermo switch. Which fan fits between the SR water pump pulley and the radiator? I have about 3” of clearance – I’ve read that a 12” slim fan works, but two 10” might be better. Any recommendations?

10. Last, the biggest question: Given my experience level and workspace, is this a 6‑month project or a 2‑year money pit? I’m prepared for setbacks, but I have to be honest with myself. What’s the single most common thing that kills an SR swap for first‑timers? Is it the wiring, the fuel system, the cooling, or just the mental fatigue? How do you push through the moments when everything is on jack stands and you can’t see the finish line?

I’ll update this thread weekly with photos (I’ll host them on Imgur and link) – even the ugly ones. I want this to be a resource for future idiots like me. If you’ve done this swap in a similar situation, please share your build thread link, your parts list, and your biggest “I almost gave up” moment. I’m all ears.

And if you’re in the Northern Virginia area and you’d be willing to swing by just to point at things and say “that’s wrong” – I’ll buy you pizza and beer. Seriously.

Thanks for reading this wall of text. I’m going to start stripping the bay this weekend. Day 1 begins now.