Nissan RB25DET Engine

1. Specifications
2. Overview, problems
3. Performance tuning

Nissan RB25 engine specs

Nissan RB25DET engine reliability, problems and repair

It is quite popular representative of RB series. It appeared in 1991 and replaced RB20DET. RB25DE used cylinder block similar to RB20, but with cylinder diameter enlarged to 86 mm. Also it was equipped with crankshaft with piston stroke 71.7 mm, new connecting rods and pistons.
Cylinder head had two camshafts with 4 valves per cylinder. The early models (to 1993) were not equipped with variable valve timing system NVCS.
RB25DE S1 camshafts: duration 240/232 deg, lift 7.8/7.3 mm. Such RB25DE S1 (Series 1) developed 180 HP at 6,000 RPM. These engines were installed on Nissan Skyline R32.
Later, in 1993 (when Skyline R33 appeared), NVCS system was used on intake camshaft. RB25DE camshafts: duration 240/240 deg, lift 7.8/7.8 mm. Thanks to RB25DE the power increased to 190 HP at 6,400 RPM. The engine was applied for Nissan Skyline R33.
Since 1995, ignition system, MAF, crankshaft position sensor and ECU were modified.
In 1998, new engine model RB25DE NEO was designed specially for Nissan Skyline R34. This engine is compliant with high ecological standards and it is equipped with new intake manifold with thin runners. Also RB25DE NEO has head with modified compression chambers, new camshafts and improved exhaust manifold. RB25DE NEO camshafts have duration 236/232 deg, lift 8.4/6.9 mm. Also such engines do not have hydraulic lifters. RB25DE NEO power increased to 200 HP at 6,400, torque 231 NM at 4,800 RPM.
Along with naturally aspirated engine, well-known turbocharged modification RB25DET was produced also.
The first version (RB25DET S1) appeared in 1993 and was installed on Nissan Skyline R33. In contrast to RB25DET, RB25DE (S1) had reinforced connecting rods, new pistons (compression ratio is 8.5), 45V1 turbocharger. The turbocharger was larger than 16V of RB20DET. Maximal boost pressure on RB25DET reached 7 psi (0.5 bar). Also that version was equipped with variable valve timing system NVCS on the intake side, fuel injector 370 cc/min, and oil jets were installed in cylinder block. The engine’s power was 245-250 HP at 6,400 RPM, torque 272 m at 4,800 RPM.
By analogy with RB25DE, in 1995 the engine was restyled: ignition system, MAF, crankshaft position sensor and also ECU were changed. Besides, it was equipped with new 45V2 turbocharger with plastic impeller instead of the steel. Those were RB25DET S2 engines.
In 1998 the engine was modified and named RB25DET NEO.
These engines were in compliance with higher ecological standards. Besides, they differed from RB25DET with new crankshaft, RB26DETT rods, modified pistons, compression ratio increased to 9, oil jets, improved intake manifold. Besides, the intake ports and combustion chambers were upgraded, head flow raised. This engine used solid lifters instead of the familiar hydraulic lifters.
RB25DET NEO camshafts: duration 236/232 deg, lift 8.4/8.7 mm. Stock fuel injectors are 340 cc/min.
RB25DET NEO engines use 45V3 turbocharger with enlarged exhaust housing and plastic impeller, boost pressure is 10 psi (0.7 bar). All these performance mods increased the power to 280 HP at 6,400 RPM, and torque 334 NM at 3,200 RPM.
Later, since 2001, 45V4 turbocharger with steel impeller was installed.
There is no need to adjust the valves on RB25DE/DET engines, since they use hydraulic lifters. But if you have RB25DE NEO or RB25DET NEO, then you should adjust valve clearance from time to time.
RB25DET/DE uses timing belt, which should be changed every 60,000 miles of mileage (90,000 km).
Besides this engine, Nissan RB series included RB20, RB24S, RB26DETT and RB30.
RB25 were discontinued in 2002 and instead, VQ25DE/DET appeared.

Nissan RB25DE engine problems and malfunctions

Similar to many legendary engines from the 90-s, RB series are highly reliable and durable. Not vainly they are the most popular engines in the world. They do not have any design failures or serious problems. Of course, some insignificant problems may still happen. Sometimes ignition coils fail, what causes complaints of misfire. In this case, you should just change the coils, and in general, change them every 60,000 miles of mileage (100,000 km). It will relieve you of such problems. Also RB25 have high fuel consumption and problems with electronics.
In other respects, these engines are quite reliable, if being served regularly and using high quality engine oil and gasoline.
Comparing RB25DET and 1JZ-GTE, one might say that 1JZ is somewhat better, and in general, Toyota engine is somewhat more reliable and it fits for performance tuning more.

Nissan RB25DE engine tuning

RB25DET Boost up

You should immediately forget of naturally aspirated tuning RB25DE or installing turbo kit on RB25DE. It is expensive, takes long time and has no sense. You will just waste your money. It is much easier, more reliable, quicker and cheaper to purchase RB25DET, and you will gain much power at once.
As to increasing the boost on stock RB25DET turbocharger, their limit is just 11.5-13 psi (0.8-0.9 bar). To make your car driving at 13 psi (0.9 bar), you need to buy 3 inch performance exhaust system, GTR front intercooler, Apexi power intake, Z32 MAF, boost controller, new spark plugs and new water pump. And also purchase GTR N1 oil pump, oil cooler, Walbro 255 lph fuel pump, Apexi Power FC (or other aftermarket ECU). With these performance parts you will gain about 300 WHP. It will let you driving 1/4 miles for mid 13 seconds. Certainly, 300HP is not what you expect from the legendary engine, so we go on.
Wishing to gain 350+ WHP, we should upgrade the previous variant. Your stock turbocharger will not promote much power, therefore you need HKS GT2835 turbocharger. Also buy fuel injectors 550 cc/min, fuel pressure regulator, Splitfire ignition coils and 3-layer radiator. Thanks to these upgrades, it will be enough to set boost pressure at 15 psi (1 bar) to gain 340 WHP. And if the boost is increased to 22 psi (1.5 bar), you will get about 400 horsepower on the wheels.
Still not enough? In this case you need GT3540 turbocharger, and also camshafts 256/256, valve springs and fuel injectors 750 cc/min. With these mods you will obtain 400 WHP at 15 psi (1 bar). Turbocharger like this lets driving quarter mile per high 11 seconds.
The main is, that you can do all this using stock pistons. Moreover, RB25DET stock internals will bear even 500 horsepower, and if you use water methanol injection kit, then even more than 500 HP. But to be sure in reliability of your engine, it is worth buying GTR rods, forged pistons, MLS head gasket, ARP studs and make head porting. Upon this more than 500-600 horsepower will be available. However, if the power is too high, cracks may appear on RB25DET cylinder block.
Besides the described above, sometimes RB26DETT head is installed on RB25DET. Also stroker kit may be used, then displacement will reach 2.8-2.9L. Some owners apply RB26DETT crank, RB26DETT pistons and 1.2 mm head gasket. It will make compression ratio 8.7 and increase displacement to 2.6L. Using 1.5 mm head gasket will diminish compression ratio to 8.4. For everything to work properly, you should close the port to NVCS system. All these performance mods are too expensive, complicated and irrational. If you wish really impressive power, then better buy RB26DETT engine.

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