Nissan RB25 vs RB26: Which is Better? 

The difference between the RB25 and RB26 engines is merely based on their power, torque production capabilities – most of the time. But what is more than that? How about the upgrades? Electrical, Mechanical, and Technical improvements. Both engines are powerful in their own right. They have enhanced turbocharged variants to improve the engine performance, but let us discuss the other engine’s edge over the other: Built-wise, upgrades, reliability, and many more.

Let’s get right to it!

The Nissan RB25 Engine

  • Production Run: 1991 – 2001
  • Cylinder Head Material: Aluminum
  • Cylinder Block Material: Cast-iron
  • Configuration: Inline-6
  • Bore: 86 mm
  • Stroke: 71.7 mm
  • Valvetrain: DOHC four valves per cylinder
  • Displacement: 2.5 L (2498 cc)
  • Compression Ratio: 10
  • Weight: 507 lbs.
  • Maximum HP: 250 HP at 6,400 RPM
  • Maximum Torque: 188 lb-ft at 4,000 RPM

The Nissan RB25 is the initial model designed as a non-turbo twin-cam machine and part of the most recognizable RB series of engines that powered specifically the Nissan Skyline GTST R33. The RB25 engine is the newer rendition and much-improved package over its predecessor RB20DET.

The RB25 is a straight-six, 2.5 Liter, non-turbocharged engine, famous for being in the skyline series, and it debuted in the R32 Nissan Skyline GTS25 sedan and coupe models. It is badged as the RB25DE engine. It is a non-VCT (variable valve timing and lift) and can produce up to 190 HP at 6,000 RPM and 183 lb-ft of torque available. Two years since its emergence, it would go on to form four iterations to present in the market: RB25DE, RB25DET, RB25DE NEO, and RB25DET NEO.

RB25 engine used the same cylinder block as its predecessor in RB20. It is made from cast iron with a larger cylinder bore diameter of 86 mm, piston stroke of 71.7 mm, and a compression rating of 8.5, along with new connecting rods and pistons.

The cylinder head is made from Aluminum that has two camshafts with four valves per cylinder – two for both intake and exhaust. Early RB25 models, especially those produced prior to 1993, are not equipped with the variable valve timing system (NVCS) – which the RB25DE engine is a part of.

However, in 1993, the first-ever RB25DET series (S1) appeared in the 1993 Nissan Skyline R33 GTST, which featured Nissan’s NVCS VVT system (Variable Valve Timing) on the intake side. That addition gave this engine a boost in power and torque production at the lower-end RPM range than its previous model. It has new pistons, reinforced connecting rods, a 45V1 turbocharger, and a larger fuel injector that provides the engine with 370 cc/min of fuel. RB25DET S1 can produce 250 HP at 6,400 RPM and 235 lb-ft of torque at 4,800 RPM in its stock form.

Two years after the S1 was released, in 1995, Nissan upgraded the S1 and restyled both previous models – RB25DE and RB25DET, into the market release of the second series (S2). This alteration featured a new 45V2 turbocharger with a ceramic turbine wheel contrary to the previous ones that use Aluminum. But the most highlighted change in this version is its revised electrical system, where ignition coils feature built-in ignitors. Some modifications include a new airflow meter, cam angle sensor, mass airflow sensor, throttle position sensor, crankshaft position sensor, and ECU.

One of the main differences between series one and series two is their camshaft. The latter’s cam angle sensors go slightly different into the exhaust cam.

Three years later, Nissan modified the engine and put a different head to the newly-launched RB25DET R34 and named it RB25DET NEO; NEO stands for Nissan Ecology Oriented. Hence the engine’s primary goal is to minimize the emissions as it is a complaint to higher ecological standards, which enabled the R34 to pass as a Low Emission Vehicle with better fuel consumption and lesser emission outputs.

The changes and additional features that came with the RB25DET NEO models include the use of solid lifters instead of the typical hydraulic lifters. These revised camshafts have a turn on and off solenoid Variable VCT, RB26DETT connecting rods, and model-specific coil packs along with a hotter 180F thermostat.

Nissan also adjusted the intake diameter with a reduced runner diameter from 50 mm to 45 mm. Two inlets are made for the manifold, increasing the air velocity going into the engine, giving the machine a more lower-end torque action. NEO head combustion chambers are smaller, so Nissan used a model-specific modified piston to compensate to go with the GT-R connecting rods, resulting in an increased compression rating of 9.0.

The RB25DET NEO engine uses a 45V3 turbocharger with a larger OP6 turbine which has a steel compressor and a ceramic turbine wheel. This turbocharged engine was upgraded, and Nissan placed a larger exhaust housing and a significant increase in power.

Even though these engines are primarily made for ecological compliance to meet the LEV criteria, the NEO version has outstanding power output. It earned one of the highest figures of all RB25DET engines, producing 250 HP at 6,400 RPM and 267 lb-ft of torque in stock form.

The Nissan RB26 Engine:

  • Production Run: 1989 – 2002
  • Cylinder Head Material: Aluminum
  • Cylinder Block Material: Cast-iron
  • Configuration: Inline-6
  • Bore: 86 mm
  • Stroke: 73.7 mm
  • Valvetrain: DOHC four valves per cylinder
  • Displacement: 2.6 L (2498 cc)
  • Compression Ratio: 8.5
  • Weight: 570 lbs.
  • Maximum HP: 316 HP at 6,800 RPM
  • Maximum Torque: 289 lb-ft at 4,400 RPM

The Nissan RB26, more technically known as the RB26DETT engine, is also a six-inline, 2.6 Liter that powered one of the most notable vehicles of our generation, the 1989 – 2002 Nissan Skyline GT-R models.

The RB26DETT cylinder block, contrary to the RB25DET, is made from cast iron but without oil ports. It has a 86 mm cylinder bore, 73.7 mm piston stroke, and an 8.5 compression rating. The redesigned pistons installed were 1mm lower and an RB25DET NEO connecting rods to link them. The block is then covered with a 24-valve DOHC aluminum-alloy head with four valves per cylinder -two for both intake and exhaust and has no variable valve system VCT.

The thing with the RB26DETT is that, instead of having a single flow of throttle, this engine has six individual throttle bodies that measure 45 mm in diameter; and these three sets are Siamesed together. However, this kind of intake system varies from other RB engines since they use single ones.

The RB26DETT, in stock form, is already installed with a powerhouse parallel-twin turbo system. The engine directs the air into the intake manifold that uses a pair of ceramic Garrett M24 set by the wastegates to limit the maximal boost pressure to 10 psi. To add to that, the Skyline GT-R has a built-in boost restrictor to restrict to keep the boost under the critical level of 13 psi.

The earliest production of the RB26 engines was rated at 280 HP at 6,800 RPM and a 260 lb-ft of torque at 4,400 RPM. However, on the tail end of its production years, the numbers ballooned to nearly reaching the staggering 320 mark at 316 HP at 6,800 RPM and a larger torque of 289 lb-ft at 4,400 RPM. Mainly due to the development and modifications made to the engine.

Unfortunately, Japanese-made vehicle cars are capped at 276 HP due to the Gentleman’s agreement made by Nissan, which states that they cannot go beyond the said number (but why?). Though it appears to be lesser in the paper, many enthusiasts believed that the numbers penned on those papers were far from the true potential of the RB26 engine and stirs some phantom ratings. The RB26DETT machines can only be found on exclusives such as the Skyline GT-R 32 and Skyline GT-R R33.

Nissan later on modified the RB26 aesthetically and some ECU fine tunings. So in the Nissan R34, they used ball-bearing Garrett M24 T28 turbochargers separating from the typical journal-bearing turbos. Nissan also added fair amounts of upgrades such as a revised coolant/heater pipe diameter on the intake side of the block, stainless dump pipes; Igniter built into coil packs; the lighter casting of the intake manifold, and dual-mass flywheel.

Engine Potential

Both engines are excellent in their own ways; though RB26 has a higher capacity than those of the RB25 engines, they can handle each of their own going into higher power outputs.

RB25 and RB26 engines are also of the same levels to the power production and the upgrades applied to them. The stock internals of both machines are of the same reputation; turbocharged variants available on both sides, and the reliability is sky-high.

No engine is inferior or superior to the other in terms of potential. But in stock form, RB26 engines have a slight edge due to the six individual throttles as well as a twin-turbo-powered engine in its stock form.

Problems Surrounding the Engines

Both are highly reliable and highly durable engines, which can be proven through the test of time. Some troubles may arise, but these engines are way too strong and can merely display their weaknesses.

Apart from that, Nissan’s technologies, upgrades, and craftsmanship reflect on what they do best.

Summary

The legendary, most recognizable, and iconic Japanese vehicle made its presence felt as it stormed the fronts of the automotive scene by the capabilities of its engine through a lower fuel consumption and produced big numbers larger than your typical inline-six out there. These powerplants are widely praised by the community as well as the industry; they became a superstar and even featured in movies.

But the unsung heroes belong to the RB engines that powered the Skyline GT-R models, especially the RB25 and RB26 engines. Made years apart, the RB26 engine is the last to emerge as a brand new self of the RB25; since most upgrades are inclined to one another. However, RB26 is more expensive in terms of price due to the features it puts on the table. Six throttle bodies, twin-turbo powered, higher capacity, and other additional updates. RB25, on the other hand, cannot also be missed even though it is not turbo installed in its stock form, the power production of the engine is not lightyears behind the RB26; just around 20-30 HP, which can be pumped through a turbo.

To top it off, RB25 made its competition feel like they lack something especially during that time. RB26 became a movement, a revolution of new generation engines reverberating throughout the world; it became a superior knowledge and work detail model.

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