What is a Nissan RB25 engine? 

It’s a frickin’ beast, that’s what!… And it spawned a whole generation of motors that powered our favorite tuner cars. First off, the RB25 base motor is the non-turbo twin-cam engine—part of the most well-known Nissan RB family. The RB25 engine is a newer and significantly improved version of its predecessor, the RB20DET.

This engine is a straight-six 2.5 liter that originally debuted in the R32 Nissan Skyline GTS25 sedan and coupe variants, with the official designation as RB25DE. It didn’t come with variable valve timing and lift at the time, and produced 190 HP at 6k RPM and 183 lb-ft of torque when it rolled off the factory floor. Here’s where it gets fun: the motor would go on to develop four more iterations popular with tuners: the: RB25DE itself, RB25DET, RB25DE NEO, and RB25DET NEO. We’re in love with every version, especially because of their tunability and power potential.

The RB25 engine had the same cylinder block as the older RB20… but has a bigger cylinder bore diameter of 86 mm, a piston stroke of 71.7 mm, and a compression ratio of 8.5. Nissan engineers also added new connecting rods and pistons. The aluminum cylinder head features two camshafts and four valves per cylinder, two for intake and two for exhaust. This 4-valve design is excellent for breathability and efficiency. Early RB25 models, particularly those manufactured prior to 1993, lack the variable valve timing system (NVCS) of which the RB25DE engine is a component.

What about the RB25 Turbo (RB25DET) engine? 

The first-ever RB25DET series (S1) emerged in the 1993 Nissan Skyline R33 GTST, which incorporated Nissan’s NVCS VVT (Variable Valve Timing) technology on the intake side—a similar system to Honda’s VTEC. Larger 370cc injectors were also needed for this thirsty monster. Then, work on the bottom end of the RB25DET brought in new pistons, stronger connecting rods, and most importantly, a 45V1 turbocharger. In factory condition, the RB25DET S1 produces a solid 250 HP and 235 lb-ft of torque. Awesome specs and great power potential, especially in the early 90’s.

Nissan updated the S1 and restyled both prior models into the market introduction of the second series two years later, in 1995 (S2). This modification included a new 45V2 turbocharger with a ceramic turbine wheel, as opposed to the previous aluminum version. The most noticeable modification in this version is the updated electrical system, which includes ignition coils with built-in ignitors. A brand new airflow meter, cam angle sensor, mass airflow sensor, throttle position sensor, crankshaft position sensor, and ECU are among the upgrades. More aggressive cams finished out the upgrades between S1 and S2.

The evolution continued three years later, where Nissan fitted a new head to the newly introduced RB25DET R34, naming it the RB25DET NEO (Nissan Ecology Oriented). These changes were mainly to decrease emissions, in order to comply with tougher environmental laws. The R34 then qualified as a Low Emission Vehicle (LEV) with improved fuel efficiency and lower emission outputs (lol)! Other upgrades: solid lifters rather than the conventional hydraulic lifters. Variable VCT, upgraded rods, newer coil packs, and a hotter 180F thermostat were also added.

On the intake side, Nissan reduced the runner diameter from 50mm to 45mm, increasing air velocity with two manifold inlets. This results in greater low-end torque. NEO head combustion chambers are also smaller, so specific pistons were introduced with GT-R connecting rods to compensate. The result? A small boost into a 9.0 compression ratio. Finally, the updated 45V3 turbocharger featured a steel compressor and a ceramic turbine wheel.

All in all, exceptional power output at 250 HP and 267 lb-ft of torque, making it one of the most powerful RB25DET engines.

RB25 vs RB26: What’s the Difference?

Most of the time, the difference between the RB25 and RB26 engines is based only on their power and torque generating capabilities. But what else is there? Improvements in electrical, mechanical, and technical systems. Both engines are quite powerful on their own. They have improved turbocharged varieties to boost engine performance, but let us review the other engine’s advantages: build, upgrades, dependability, and many more.

What is the Nissan RB26DETT engine?

The Nissan RB26, often known as the RB26DETT engine, is a six-inline, 2.6 Liter engine that powered one of our generation’s most iconic automobiles, the 1989 – 2002 Nissan Skyline GT-R models. You would also find it in the killer, undefeated, Calsonic Nissan GT-R R32!

In contrast to the RB25DET, the RB26DETT cylinder block is composed of cast iron but lacks oil ports. It has a cylinder bore of 86 mm, a piston stroke of 73.7 mm, and a compression ratio of 8.5. The revised pistons were positioned 1mm lower and were linked by RB25DET NEO connecting rods. The block is then topped with a 24-valve DOHC aluminum-alloy head with four valves per cylinder—two for intake and two for exhaust—and no variable valve system VCT. The RB26DETT engine also upgraded to six separate, individual throttle bodies, 45 mm in diameter each.

In standard configuration, the RB26DETT already has a powerful parallel-twin turbo system. The engine pushes air into the intake manifold, which employs a pair of ceramic Garrett M24 wastegates to limit the maximum boost pressure to 10 psi.

The RB26 engines were initially rated as 280 HP and 260 lb-ft of torque. However, at the conclusion of its manufacturing run, Nissan engineers pushed upwards closer to 317 HP with a fatter torque curve to 289 lb-ft, mostly through breathability and tuning updates.

Nissan later changed the RB26’s appearance and made minor ECU tweaks. In the Nissan R34, ball-bearing Garrett M24 T28 turbochargers were utilized instead of the standard journal-bearing turbos. Nissan also included a reduced coolant/heater pipe diameter on the intake side of the block, stainless dump pipes, an igniter incorporated into the coil packs, a lighter intake manifold casting, and a dual-mass flywheel.

Tuning Potential 

Both engines are great in their own right. While the RB26 is slightly larger in displacement than the RB25, they are quite similar in total output, with forum users seeing anywhere from 500whp to 600whp. Both are extremely dependable and long-lasting engines that have stood the test of tuners and their insatiable want for more power. Some issues may develop—malfunctioning ignition coils, oil pump flow problems—but upgrading these components are key when you’re looking at higher horsepower builds anyway. Aside from that, Nissan’s technology and workmanship on the RB motor series is absolutely top notch.

Tuners have also been stuffing these motors into other chassis’. Check out this jaw-dropping build that hit $96k on Bring-A-Trailer.

Summary

Arguably the most revered and identifiable, iconic Japanese tuner car out there—the Nissan Skyline—captivated us, thanks to one hell of a powerplant. The RB received widespread acclaim from the public and the industry, showing up with celebrities and within films.

Though the RB26 is usually more expensive (six throttle bodies, twin-turbo power, etc), the RB25 can’t be overlooked. The family of RB engines will forever live in tuner lore.