Nissan RB25DET – Complete Engine Guide

by Staff | Last updated 17th February, 2021 | Posted in Guides

We cover everything you need to know about Nissan’s RB25DET six-cylinder engine.

rb25det 240sx swap

When most people debate about the best Nissan engines to ever come out of Japan, especially during the 90s, the Nissan RB engines are often name-dropped in the conversation.

Arguably, one of the most renowned power plants in the RB engine family is the RB25DET.

Even though it’s underrated when compared to the mighty RB26DETT, the Nissan’s RB25DET engine is a fine piece of engineering work; it’s very reliable, tuneable and sounds fantastic.

But let’s not get ahead of ourselves (we’ll get down to that in a minute), and first, understand everything about Nissan’s RB25DET engine.


A Brief History

Nissan’s RB25DET engine burst onto the scene in 1993 when it was used in the R33 Nissan Skyline GTST. It was introduced after Nissan ceased the production of its predecessor (the RB20DET) in the same year.

In contrast to the previous RB engine model, the RB25DET came with more torque and power at lower rpm; thanks to the upgraded Nissan Variable Cam System (NVCS) on the intake camshaft.

It also came with larger injectors, improved pistons, reinforced connecting rods, and a bigger 45V1 turbocharger.

A few years later in 1995, Nissan made a few adjustments by including ignition coils with built-in ignitors on the electrical system and switched the aluminum wheel on the turbocharger with a ceramic turbine wheel. The new revised RB25DET engine was known as the series 2.

Sure, there were other minor changes such as a new airflow meter, cam angle sensor, ECU, and throttle position sensor but there wasn’t much of a big mechanical difference between series 1 and series 2 except the cam angle sensor’s shaft.

Otherwise, both series 1 and series 2 still came with 250 hp and 235 lb-ft torque.

However, the major difference came when Nissan introduced the RB25DET NEO in 1998.

It packed 280hp and 268lb/ft torque straight from the factory; despite its low emission vehicle (LEV) engine status due to lower fuel consumption.

Beyond that, the RB25DET NEO included a revised intake manifold with a smaller runner diameter (45 mm) to improve the air velocity and low-end torque.

The NEO head replaced hydraulic lifters with solid lifters, and the camshafts were upgraded with a solenoid variable VCT; plus, the engine included a hotter 82 °C thermostat.

Truth be told, the NEO head that was introduced in 1998 is a slightly better engine with stronger internals than the original RB25DET that came out in 1993.

The only problem is the aftermarket parts for RB25DET NEO are very hard to find since they were available in the market for a short period.


Manufacturer Specs

  • Production Run: 1993 – 2002
  • Displacement: 2498cc
  • Cylinder Block Material: Cast Iron
  • Cylinder Head Material: Cast Aluminum
  • Configuration: Straight-6
  • Valvetrain: DOHC | Four Valves per Cylinder
  • Stroke: 71.7mm
  • Bore: 86mm
  • Compression Ratio: 8.5:1 |RB25DET (9.1|RB25DET NEO)
  • Horsepower: 245hp to 250hp|RB25DET (280hp|RB25DET NEO)
  • Torque: 235 lb-ft|RB25DET (267 lb⋅ft |RB25DET NEO)
  • Fuel Type: Gasoline
  • Oil Change Interval: 5,000 to 10,000 km
  • Normal Operating Temperature: 90 °C

Here is the engine code deciphered for you:

  • RB: Engine Family
  • 25: 2.5L Displacement
  • D: Dual Overhead Cam
  • E: Electric Fuel Injection
  • T: Factory Turbocharger

Another thing: The RB25DET is identical to the RB25DE with almost the same specifications except that RB25DET is factory turbocharged.

For that reason, the RB25DE is a naturally aspirated engine with 182 to 200 hp.

Which Cars Are Compatible with RB25DET Engine?

We’ve seen trucks such as the Nissan Patrol, Nissan Patrol, BMW E36, to a Volvo Wagon swapped with an RB25DET engine; albeit it can be complicated to pull it off.

Something like this Nissan Patrol swapped with an RB25DET engine would give you goosebumps on the road.

However, if we’re talking about cars that came with the RB25DET engine, we have:

  • Nissan Skyline R33/ R34 GTST
  • Nissan Cedric Y34
  • Nissan Stagea WC34
  • Nissan Laurel C34 & C35
  • Nissan Gloria Y33 & Y34

Better yet, you can even put an RB25DET engine on a 240SX S13 chassis to improve its performance. If you want to know how it can be done, watch the video below.


240SX RB25DET engine

If you’re going to swap your KA engine with an RB25DET engine, there are a few things that you’re going to need. Let’s have a look:

  • 1. For starters, after you’ve removed the KA engine, you can stitch weld every seam in the engine bay. This will make it easier to install.
  • 2. Re-paint the engine bay for a nice, clean, and smooth finish. Also, add a primer to prevent rust.
  • 3. Next, you need to install some new engine mounts. Something like the Xcessive VH45 S13 would be ideal.
  • 4. Install a new wiring system. In that case, you will probably need the 240SX Non-Neo Wiring Harness that is straight-up plug-and-play with no additional wiring required.
  • 5. If you want, you can update the gauges on the dashboard since you will be adding a more powerful engine.
  • 6. If you want to tune the engine and boost the power, it makes sense to modify it at this stage before you proceed to install the RB25DET engine.
  • 7. After you’ve tuned the engine with all the necessary parts, cover the front end with shields.
  • 8. Add a compatible lightweight flywheel and clutch to the RB25DET engine.
  • 9. Bolt the transmission into the engine.
  • 10. Slowly mount the RB25DET on the engine bay. Make sure there is enough ground clearance.
  • 11. Confirm the wiring is done correctly and test the new engine. If you notice anything off, you should work on it.

Note: Swapping the KA engine in 240SX is complicated. If you don’t have the expertise, it’s better to consult a qualified mechanic for the job.


Tuning The RB25DET

We’ve not really gone into the specifics, but if you want to tune an RB25DET engine and take it to the next level, what should you do?

Stage 1 Modifications

At this stage, the best you could aim for would be 300hp. Of course, you don’t need to upgrade the turbocharger at this phase.

However, some of the supporting mods that you may require include; sports exhaust manifold, fast road camshaft, intake headers, boost controller, front mount intercooler, panel air filters, piggyback ECU, and Z32 massive air flow sensor.

Even though it could be a little bit tempting, we don’t advise going beyond 11.5 to 13 psi at this level since you will be using a stock turbocharger.

Stage 2 Modifications

If you want to achieve at least 350hp, you will need to modify your engine with high-flow fuel injectors, ported and polished head, a high-performance exhaust system, and an induction kit.

On top of that, you need to think about upgrading your turbo, fuel pump, oil cooler, and oil pump.

Stage 3 Modifications

What if you want to go all in and squeeze the RB25DET engine to 400hp and beyond? It’s possible, but it could be expensive.
To make it happen, you have to first upgrade the internal engine parts so that you can have bigger valves and ported cylinder heads.

Next, you have to modify the crank and piston to alter compression; plus, balance and blueprint the engine for a smoother and consistent performance.

Of course, you have to put in some serious aftermarket turbochargers at this stage.

The trick is to force as much air and fuel as possible into the RB25DET engine so that you can maximize horsepower. Hence, it begs the question; can you go full retard on an RB25DET engine and achieve 500hp?

Yes, you can do that but it requires a lot of work and sourcing a different range of aftermarket parts.

For instance, you could fit an RB26DETT head on an RB25 block and use quality stroker kits to improve the displacement to 2.8 or 2.9 L.

Then again, if it’s too expensive, why not go for a stock RB26DETT engine and tune it for maximum output?

Here is an interesting breakdown of an RB25DET engine with 550hp.


Common RB25DET Issues

The RB25 engine has a solid reputation due to its durability and reliability. As long as you change the oil and service the engine without skipping the recommended intervals, it will run almost forever with no serious issues.

However, there are a few minor weak spots on the RB25DET engine that you should know:

  • 1. If you push the stock ceramic turbo beyond 0.9 bar boost or 13psi, you could have a premature turbo failure. However, you can avoid that by swapping it with an aftermarket turbo kit that can handle more boost.
  • 2. Don’t overfill the engine with oil beyond the ‘full’ line on the dipstick. This could cause bearing failure due to oil surge especially when you’re cornering at high speed.
  • 3. If you’re drag racing or drifting with an RB25DET engine for a long period, it’s common to find excess oil leakage in the cylinder head and catch can. You can solve it by connecting an external oil hose from the cylinder head to the oil sump.
  • 4. Sometimes the oil runs too hot when you push the engine too hard or if you’re driving in hot climates. For that reason, we recommend that you install an oil cooling system.
  • 5. The cam angle sensors can malfunction occasionally. But that is something that can easily be fixed by a swap.
  • 6. Sometimes the ignition coils can misfire but you can swap if it happens. Also, you should change the ignition coils after every 60,000 miles.

Conclusion

It’s no secret that the RB25DET engine is not the most powerful in the RB engine series; the RB26DETT engine is way more powerful.
However, don’t underestimate the RB25DET engine; it can still kick ass on the drift scene.

We’ve seen modified RB25DET engines on 240SX with a lot of power to blow your socks off!

Not to mention, RB25DET engines are durable and reliable with no major mechanical issues and if you tune it to its full potential, you can achieve up to 500hp.