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The comprehensive guide to the RB25 Engine

"All you need to know about RB25DET Engine Tuning"

With the help of TMS Motorsport we are pleased to provide an all you need to know guide to tuning the popular RB25 engine. This has to rate as one of best engines to base a tuning project on, with massive tolerance of power gains, and many tuning part options.

Please note that cars fitted with the Tiptronic require a totally different approach to tuning, as the gearbox can't handle major power gains. (Triptronic are R34 only. R33 are Normal 4 speed Autobox with snow, power and economy mode)

Before you start, please have a goal in mind. TorqueCars hate to see the pick and mix approach to tuning, where various parts are just added to see what the power gains are then they are swapped out or other parts added. So set a power goal and then look at the components you'll need to achieve this.

We would suggest that the following bhp targets of 300, 350 and 450 are good targets, as they have fairly clear upgrade paths. Anything over 500 requires quite extensive work and a totally different range of parts so if this is your ultimate goal bear this in mind when fitting and sourcing parts.

 

6 Cylinder 2,498cc 24v valve turbo engine.

RB25DE - NON-TURBO twin-cam 180 - 200 hp @ 6000 rpm,

RB25DET - twin-cam TURBO (T3 Turbo) 245 to 250 hp

The NEO head fitted from 1998 helped with emissions, it also had solid lifters and used a different cam profile.

RB25DE NEO- NON-TURBO twin-cam 219 hp @ 6000 rpm

RB25DET NEO - twin-cam TURBO 276 hp @ 6400 rpm

  • Spec 1 – Has an ignition amplifier. Coil packs are marked I + E, coil pack loom is different, therefore engine loom is slightly different. There were from early 1993 to 1994, but doesn’t seem to be a hard and fast rule. The S1 also had an aluminum compressor wheel, later editions were ceramic.
  • Spec 2 – Engine doesn’t have ignition amplifier. Coil packs are marked IB G +, coil pack look is different, which makes engine loom slightly different. Camshaft angle sensors were revised for a Mitsubishi CAS (early ones suffered from broken positioning teeth though so the Black CAS was introduced.)
  • Spec 3 - Engine on very late R33, very few about. From late 1997 onwards. They run different camshafts, the Crank Angle sensor which went on to be used in the R34 RB25DET Neo engine.

Standard Boost is 2 stage. 0.5 bar until NVCS (about 4.5k revs), then 0.7 bar until 7k rev standard rev limit. This helps maintain fuel economy and keeps it drivable in slow traffic, the stage 2 boost option is usually the first thing an RB25 tuner will do and makes an easy power gain.

The mod involved quite simply cutting the black wire on the solenoid and connecting this to ground on the car body, forcing the car to stay in stage 2 boost all the time. There are plenty of detailed step by step instructions around in our forum, and many popular skyline forums out there.

Another way to achieve higher boost at low rpm is by fitting a boost controller. You can usually set this to 0.85 bar on a standard turbo.

The heads were pretty much the same on the R33. The NASP (naturally aspirated, non turbo) engines don't have water and oil lines to the turbo (obviously).

Weak spots/problems with the RB25 engines?

Running more than 0.9 bar boost on standard ceramic turbo causes premature turbo failure.

Oil cooling required on spirited use, these run quite hot so keep an eye on the oil temps.

Oil surge on high speed cornering leading to bearing failure (People often overfill standard engine by about ½ litre or more when on track, up to the H on the dipstick which is about 10mm over the full line)

  • After 300 bhp you'll need an upgraded ECU.
  • At 320-340bhp and greater you should uprate the turbo, head gasket, clutch, airflow meter and injectors.
  • Pistons are generally good for 500bhp.
  • The RB25 block can be rebored from the standard 86mm to 86.5 or 87mm.

Fuelling

The R33 GTR Fuel pump is a straight drop in and good for 500 odd BHP so becomes and obvious choice for the tuner, with the added benefit that these are quite easy to source in the used markets.

The standard fuel injectors usually hit the maximum at around 350BHP. GTR ones don’t fit, unless modified and you use GTR injector ballast (different feed and impedance) so most people go to 55cc injectors, similar to those on the better Subaru Impreza engines.

What are the best turbo upgrades and what power figures do these support, mention a bolt on swap and also list the more complex turbo upgrades and hybrid options.

R34 GTT turbo is a little bit bigger. My preference would be 3037 garret or HS 2835 for around 400 ish bhp, more than that get a bit pointless on the road !

Looking over the exhaust you could fit a 75mm downpipe which improves Torque and BHP by upto 35lbft and 25bhp in some cases. Then taking off the catalyst (an off road mod in most countries) will give another 10 bhp.

Please help us to complete this article, use the feedback box below if you spot any errors or have any tips or comments to pass on to other RB25 engine tuners.

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