Understanding the RB20DET Engine

The RB20DET is a 2.0‑liter, turbocharged inline‑six engine originally found in the Nissan Skyline (R32, R33, and Laurel). It delivers approximately 200 horsepower and 200 lb‑ft of torque from the factory, but its cast‑iron block and robust bottom end make it a stout platform for further modification. The RB20DET is often chosen over the more common SR20DET because of its smooth six‑cylinder torque curve, distinctive exhaust note, and the ability to rev higher with proper tuning. Many enthusiasts consider it a “gateway” RB engine—easier to source and cheaper than the larger RB25DET or RB26DETT, yet still capable of 350 hp with bolt‑on parts and a tune.

Key specifications to keep in mind:

  • Displacement: 1,998 cc (2.0 L)
  • Configuration: Inline‑six, 24‑valve DOHC, turbocharged
  • Factory output: ~200 hp @ 6,400 rpm, ~200 lb‑ft @ 3,200 rpm
  • Compression ratio: 8.5:1
  • Turbocharger: Single Garrett T25 or T28 (depending on generation)
  • Engine management: Nissan ECCS with MAF sensor

Because the RB20DET uses a timing belt (rather than a chain), it’s important to verify belt condition and replace it if age or mileage is unknown. The engine also has a well‑known tendency to crack exhaust manifolds under high heat; a tubular manifold is a common upgrade that also reduces weight.

Why Swap an RB20DET into a 240SX?

The S13/S14 240SX chassis is light, rear‑wheel drive, and responsive. Swapping in the RB20DET offers several advantages over both the stock KA24DE and the popular SR20DET swap:

  • Smooth power delivery – The inline‑six has excellent primary balance, producing a turbine‑like pull that a four‑cylinder cannot match.
  • Cost‑effective – A complete RB20DET front‑clip (engine, transmission, harness, ECU) can often be found for less than $2,000, undercutting an SR20DET swap by $500–$1,000.
  • Tuning potential – With a good intercooler, injectors, and a standalone ECU, 350 whp is realistic on a stock long‑block.
  • Exhaust note – The RB inline‑six has a distinctive, musical tone that many enthusiasts prefer over the rasp of a four‑cylinder.
  • Future upgrade path – If you later decide you want more displacement, you can upgrade to an RB25DET or RB26DETT using the same mounts and most of the same ancillary parts.

The main downside is the limited aftermarket support compared to the SR20DET, but parts availability has improved thanks to online communities such as Zilvia.net and specialty retailers like Enjuku Racing. Additionally, the RB20DET is slightly longer than the KA24, so you may need to clearance the chassis with a small hammer for the steering shaft clearance on some S13s.

Budget Overview: Under $4,000 Goal

The original target of $4,000 is realistic if you source parts carefully, do all the labor yourself, and reuse some 240SX components (like the stock driveshaft, differential, and many sensors). This article will give you a detailed cost breakdown with high/low ranges, plus tips to keep the total under four grand. Keep in mind that prices are fluid—they vary by region, season, and current market demand for JDM engines.

Where to Find a Cheap RB20DET

The biggest cost variable is the engine and transmission package. Here are the typical sources:

  • JDM engine importers – Retailers such as JDM Racing Motors, JDM Engine Zone, or local import yards often sell complete RB20DET front‑clips for $1,200–$1,800. These include the engine, transmission, ECU, engine harness, alternator, and sometimes the intercooler and piping.
  • Private sellers on forums – Check Zilvia, Facebook Marketplace, and Craigslist. A used RB20DET with low miles (80k–120k km) can be had for $700–$1,000, but you’ll need to buy the transmission separately.
  • Auction / salvage yards – If you’re patient, you can pull an RB20DET from a crashed Skyline R32 at a salvage auction for under $500, but that requires time, tools, and the ability to handle customs paperwork in some cases.

Pro tip: Always insist on a compression test and inspect the turbo shaft play before buying. A blown turbo or low compression on one cylinder can quickly erase any savings.

Essential Parts List

Below is a thorough breakdown of every major category you’ll need. Prices reflect current market averages in the U.S. (2025).

1. Engine and Transmission

  • RB20DET long block: $800–$1,500 (if buying separately)
  • RB20DET transmission: $300–$700 (get the FS5W71C from the R32—it’s the same as the Z32 non‑turbo transmission and very durable)
  • Complete front‑clip package: $1,200–$1,800 (most budget‑friendly route)

Note: If you buy a front‑clip, you may also get the intercooler, piping, and sometimes the steering rack. These parts can be sold to offset costs.

2. Engine Mounts and Wiring Harness

  • Engine mounts: $150–$350. You can purchase prefabricated mounts (e.g., from McKinney Motorsports or ISR Performance) or weld your own using the stock 240SX crossmember. Budget mounts from Chinese sellers on eBay work if you reinforce the welds.
  • Wiring harness: $0–$400. The cheapest route is to modify the stock RB20DET harness to work with the 240SX chassis. This involves extending wires for the alternator, starter, and gauges. Pre‑made swap harnesses (e.g., from Wiring Specialties) cost $350–$450 but save many hours of frustration.
  • ECU: Included with the engine. You might consider a reflash or a Nistune board eventually, but the stock ECU will run the engine fine.

3. Cooling System

  • Radiator: $80–$200. A Koyo or Mishimoto radiator for the 240SX works if you use a 90‑degree silicone hose from the RB thermostat. Some guys use a $60 CSF all‑aluminum unit from Amazon.
  • Radiator hoses: $30–$60. Silicone hose kits are cheap and last forever.
  • Electric fan(s): $30–$80. The engine‑driven fan won’t clear the radiator if you go with a thicker core. A narrow thin‑line pusher fan is often used.
  • Coolant: $20.

4. Exhaust System

  • Turbo downpipe: $80–$200. The RB20DET has a unique flange; you can buy a bolt‑on 3‑inch downpipe from ISR or CX Racing. Used ones are often available for $50.
  • Exhaust (cat‑back): $100–$300. A generic 3‑inch exhaust for the 240SX will work, but you may need to have the flange changed to match the downpipe. Drift‑style mufflers are cheap.
  • O2 sensor bung: $10 (if you need to weld on a new bung for the wideband).

5. Fuel System

  • Fuel pump: $80–$120. Walbro 255 lph is the standard; any in‑tank pump for a 240SX will work.
  • Fuel injectors: $80–$200 (used). Stock RB20DET injectors (370 cc) are adequate for stock power, but if you plan to tune, get 550 cc or 740 cc from a Nissan Z32 or from DeatschWerks.
  • Fuel pressure regulator: $30–$70 (optional; stock FPR is fine at low boost).
  • Fuel lines: $20–$40 for high‑pressure rubber hose and clamps.

6. Clutch and Driveline

  • Clutch kit: $120–$250. The RB20DET uses a pull‑type clutch with a 225‑mm disc. You can use a stock replacement or a heavier duty kit from EXEDY or ACT.
  • Pilot bearing and throwout bearing: $20–$40.
  • Driveshaft: $0–$150. The stock 240SX driveshaft will bolt to the RB transmission if you have a flange adaptor or if the transmission is from an R32. Many builders opt for a shortened driveshaft for ~$150.
  • Clutch master and slave cylinder: $50 (if replacing old units).

7. Cooling and Fluid System

  • Intercooler and piping: $100–$300. A front‑mount intercooler kit for the 240SX (e.g., from CX Racing) will work if you buy a universal kit and route piping. The RB20DET’s turbo outlet faces the driver’s side of the car; you may need to buy a silicone coupler to reach the intercooler.
  • Blow‑off valve: $70–$150 (stock RB valve is prone to leaking at higher boost; a used Greddy or HKS is a better choice).

8. Miscellaneous Parts and Hardware

  • Oil filter and oil: $30
  • Spark plugs: $20 (use NGK BCPR7ES for stock boost, one step colder for higher boost)
  • Coolant hoses from heater core: $10
  • Vacuum lines, zip ties, wire connectors, fuel line clamps: $50
  • Chassis hammering tools: $0 (just a hammer and some tape)
  • Engine crane rental or purchase: $50–$150 (often you can borrow one from a friend)

Total Estimated Cost Summary

Here’s a realistic “low‑end” and “high‑end” breakdown for a full swap, assuming you reuse as many 240SX parts as possible (e.g., driveshaft, differential, wiring modifications instead of a pre‑made harness):

  • Engine + transmission: $1,200 – $2,000
  • Mounts + wiring adaption: $250 – $500
  • Cooling system: $130 – $280
  • Exhaust (downpipe + cat‑back): $200 – $500
  • Fuel system (pump + injectors): $180 – $320
  • Clutch + driveshaft: $150 – $400
  • Intercooler + pipes + BOV: $170 – $450
  • Miscellaneous (fluids, gaskets, wiring supplies): $150 – $300

Grand total: $2,430 – $4,750. With careful shopping, you can absolutely hit the $4,000 ceiling—and often come in under it if you wait for deals on the major components.

Hidden Costs and Tips to Stay Under $4,000

Many budget builds blow their budget on “nickel‑and‑dime” expenses that aren’t accounted for at the start. Here’s how to avoid that:

  • Replace the timing belt and water pump before installing. A failure after installation means pulling the engine again. A quality Gates belt plus water pump costs about $80.
  • Seal the oil pan. The RB20DET’s oil pan gasket is a reusable metal one; reuse it, but apply a thin bead of silicone at the corners. Don’t buy a new pan unless the old one is dented.
  • Check the turbo. If the shaft has more than 1 mm of play, you’ll need a rebuild kit ($50) or a used upgrade ($200). Rebuilding is cheaper.
  • Use the stock 240SX differential. The S13’s open diff is fine for low power, but if you plan to drift, budget $150 for a welded or VLSD unit.
  • Skip the fancy engine management initially. Stock ECU + a tuning chip (Nistune) costs ~$300 and is sufficient for up to 350 hp. Save standalone ECUs for later.
  • Join forums and local car groups. You can often get leftover parts for free—or at least cheap—from someone else’s unfinished project.
  • Do your own wiring. The RB20DET harness is not complicated. Spend $30 on a solder iron, heat shrink, and a multimeter. There are plenty of wiring diagrams on Zilvia.

Step‑by‑Step Installation Outline (Cost‑Focused)

This is not a full guide but a high‑level checklist so you can plan your time and money:

  1. Remove old KA24DE engine and transmission. (free, but budget a weekend)
  2. Prepare the RB20DET. Replace timing belt, water pump, spark plugs, valve cover gasket, and clean the intake ports. (Cost: ~$120)
  3. Modify the engine mounts. Weld or bolt the RB mounts to the 240SX crossmember. (Cost: $150–$350)
  4. Install the engine and transmission. Use an engine crane. (Rental: $50–$100)
  5. Route the wiring harness. Modify the RB harness with a 240SX chassis side plug. (Cost: $0–$400)
  6. Install the cooling system. Radiator, hoses, fan. (Cost: $100–$200)
  7. Install the exhaust. Downpipe, cat‑back. (Cost: $200–$500)
  8. Upgrade the fuel system. Pump, injectors, lines. (Cost: $180–$320)
  9. Bleed the clutch. Use existing 240SX pedal/master. (Cost: $0–$50)
  10. Start the engine. Check for leaks, set base timing, and break in the clutch.

If you get stuck, resources like YouTube swap videos and the 240SX Tech website offer free walkthroughs. Many of these videos show exactly which holes to clearance and how to wire the sensors.

Conclusion

Swapping an RB20DET into your Nissan 240SX for under $4,000 is not a myth—it’s a well‑worn path that many budget‑minded enthusiasts have followed. The key is to prioritize the major parts (engine, transmission, mounts) and scrimp on less critical items by buying used, reusing stock parts where possible, and doing all the labor yourself. With a solid front‑clip deal and some patience on forums, you can have a smooth‑revving six‑cylinder 240SX without breaking the bank. The RB20DET may not be the most powerful engine Nissan ever made, but for the money, it delivers a driving experience that justifies every penny spent.