RB25 has to be the most popular engine coming out of Nissan’s RB series of engines. You can’t miss this engine as it can be found in various configurations and referred to as one of the best engines to work on by enthusiasts.
RB25 engine is a member of the RB family produced in 1991 and became famous for its display in the prestigious JDM, R32s, R33s, and R34s. Just by looking at those cars, it can give you speed vibes. Anyway, RB25s are the engine choice of most gear-heads, but the final models were ruled out following the release of its successor in 2002, the VQ25DET. Other than Rb25, included in the RB series are RB20, RB24S, RB26DETT, and RB30.
But, after its 15-year hiatus, Nissan continued its production in 2019, putting a smile on our faces as we witness yet another episode of RB greatness. So today, we will talk about the legendary RB25 engine, its power, specifications, issues, the overall impact on the industry, and its contribution and legacy.
Engine Specifications and Design
- 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 4 Valves Per Cylinder
- Displacement: 2.5 L
- Compression Ratio: 8.5, 9.0, and 10.0
- Weight: 507 lbs.
- Max HP: 280 HP
- Max Torque: 268 lb-ft
In 1991, Nissan unveiled one of the most prominent and one of the most recognizable engines of our generation, the RB25. RB25 is an inline-6, 2.5 L petrol engine and debuted in the R32 Nissan Skyline GTS25 sedan and coupe models. It is badged as the RB25DE engine, a non-VCT, non-turbocharged model that can produce 190 HP at 6,000 RPM. And after two years since its arrival, it would go on to form four iterations to present to the market, namely: RB25DE, RB25DET, RB25DE NEO, and RB25DET NEO.
RB25 engines used a similar cast-iron cylinder block to RB20, which it replaced, but with a larger cylinder diameter of 86 mm, camshaft with a piston stroke of 71.7 mm, and new connecting rods and pistons. Its cylinder Aluminum cylinder head has two camshafts with four valves per cylinder. Early models of RB25s, particularly those that were produced before 1993, are not equipped with variable valve timing system NVCS – which RB25DE is a part of.
But in 1993, the first-ever series (S1) RB25DET appeared in the 1993 Nissan Skyline R33 GTST, which featured Nissan’s NVCS VVT (Variable Valve Timing) system on the intake cam that gave this engine more power and torque at lower-end RPM range than its previous model. It has reinforced connecting rods, new pistons with an 8.5 compression ratio, 45V1 turbocharger, and larger fuel injectors that provide the engine with 370 cc/min of fuel that can produce 250 HP at 6,400 RPM and 235 lb-ft torque at 4,800 RPM coming straight from the factory.
Two years later, in 1995, Nissan took it a step further and restyled both the RB25DET and RB25DE, releasing the second series or series 2 (S2) to the market. This alteration featured a revised electrical system and a new 45V2 turbocharger, which has a ceramic turbine wheel rather than the Aluminum wheel found in the previous S1. Some key changes in S2 were highlighted through the electrical system department, where ignition coils that featured built-in ignitors were introduced. Other modifications also include:
- A new airflow meter.
- Mass airflow sensor.
- Cam angle sensor.
- Throttle position sensor.
- Crankshaft position sensor.
The main mechanical difference between the S1 and S2 is their camshafts. S2 cam angle sensor’s shaft goes slightly different into the exhaust cam. Other than that. Mechanically wise, they don’t have much comparison.
And on 1998, Nissan modified the engine and fitted the NEO head to the newly-launched RB25DET R34 and named it the RB25DET NEO. This engine is released mainly for emission purposes as it is a complaint to higher ecological standards, which enabled the R34 to pass as a Low Emissions Vehicle with its less harmful emission output and better fuel consumption.
The changes and features that came with RB25DET NEO models include the use of solid lifters instead of hydraulic lifters, revised camshafts that featured an on/off solenoid Variable VCT, RB26DETT rods, and model-specific coil packs along with a hotter 82C thermostat.
The intake manifold was also revised by reducing the runner diameter from 50 mm to 45 mm. Two inlets came into the manifold, increasing the air velocity, which gave the car a more lower-end torque action. Combustion chambers of the NEO head are also smaller, so the model-specific modified pistons are used to compensate, along with the GT-R spec connecting rods, resulting in an increased compression ratio of 9.
RB25DET NEO engines use a 45V3 turbocharger with a larger OP6 turbine which some came with steel compressor and turbine wheels, in this case, a nylon plastic compressor wheel and ceramic turbine wheel. This turbo engine was upgraded and had a larger exhaust housing and an increase in power.
Despite being made solely for ecological and emission compliance to meet the LEV emission criteria, the NEO version did not disappoint and delivered the special order. This engine earned one of the highest figures of all the RB25DET engines, producing 280 HP at 6,400 RPM and 267 lb-ft of torque at 3,200 RPM in stock form.
You can find RB25DET engines in both R33 and R34 Nissan Skyline GTS-T models. But, what is the difference between the NEOs and non-NEOs? We discussed the specifications above. To elaborate, NEOs are innovative as they changed the various aspects of the RB25DET machine from the earlier models; one of them is the use of solid lifters. But, RB25DET reign and one of the best aspects of it is having a strong transmission.
Engine Tuning, Upgrades, and Modifications
Installing a turbo kit on an RB25DE engine is a total waste of time and money. For RB25DE, engines were released from the factory with a turbocharger attached to it, the RB25DET. However, that is just a prelude to what’s to come to your RB25DET, and it can still be boosted up.
To increase the boost on your stock RB25DET turbocharger, you need to raise its boost pressure. The rated limit of the stock turbocharger pressure is between 11.5 – 13 psi. To reach 13 psi, you need to buy a GT-R front intercooler, 3-inch performance exhaust system, Apexi power intake, boost controller, Z32 MAF, new water pump, and spark plugs. You will also need a GT-R N1 oil pump, oil cooler, aftermarket ECU, Walbro 255 lph fuel pump. With these upgrades, you can achieve 300 HP.
But if you want to reach the 350 HP mark, you will need to replace your stock turbocharger with a new one. The stock one can’t provide more power to reach that level, so upgrading to HKS GT2835 turbocharger would suffice. Also, buy a fuel pressure regulator, 550 cc/min fuel injectors, spitfire ignition coils, and a 3-layer radiator. I will not only gain you more horsepower, but it will also increase your boost pressure to 15 psi.
If that still not enough for you, we still have something in the bag. You will need to need a GT3540 turbocharger, 750 cc/min fuel injectors, valve springs, and 256/256 camshafts. However, even though the stock internals can withstand such high power outputs, even up to 500 HP, it is still better to back it up and keep the reliability high for the engine by buying forged pistons, MLS head gasket, GT-R rods, ARP studs, and do some head porting. We did this so we can prevent cracks and crevices to the RB25DET cylinder block.
Just like any 90s engine, RB25 engines are highly reliable and durable. However, they are still minor issues that might arise despite its excellent design. Sometimes the ignition coils do fail and cause misfiring. You need to replace the coils and have a scheduled 60,000-mile replacement to ease problems like this in this issue.
RB25s are also subjected to some electronic problems and high fuel consumption. The latter is not an extraordinary problem. We know that high-power engines demand more oil due to their high-speed nature.
I want to add also to change the timing belt every 60,000 miles if you are using the RB25DE/RB25DET engines and valve adjustments every 60,000 miles if you have RB25DE NEO or RB25DET NEO.
Premature turbo failure might also occur on some occasions, as running more than 13 psi on a standard ceramic turbo might cause some troubles. With that, Oil cooling is highly recommended.
Oil surges might also contribute to some issues, as high-speed cornering can lead to a bearing failure.
But importantly, don’t forget to use high-quality engine oil and proper maintenance.
RB25 engines are iconic and, at the same time, a movement. Its impact on the automotive industry and community is overwhelming. Whenever you see any GT-R on the streets, you can’t help yourself to stand in the same road with this special machine, indeed a sight to behold. At the same note, it does not deprive us of power as it produces high power even coming straight from the factory and the best of all is you can tune it depending on your liking. Nothing beats a personal car based on your own preferences. Though it has some issues, it is outside the design and caused mainly by external factors. Overall, RB25 engines are highly reliable and can last a lifetime with proper maintenance, not compromising engine oil quality and gasoline.
I hope that we cleared some confusion in your head regarding the RB25 engines. May this serve as a simple guide for understanding the engine that governs the iconic R33s and R34s.