Replacing the engine in a Nissan 240SX with an RB25 engine is done for many reasons. The rear-wheel drive 240SX has a natural balance, even weight distribution and good grip; it is also inexpensive. The RB25 is a racing engine that fits into the Nissan 240SX without many problems. The 240SX models produced between 1989 and 1994 are recommended for this engine swap, as they are about 300 pounds lighter than the newer S14 models.
Remove the engine from the car, including the engine wiring harness, radiator and hood.
Disconnect the fuel lines and drain any remaining fuel from the lines.
Unbolt the drive shaft and disconnect the heater hoses. Leave the hoses in the car, as they will slip right onto the RB25.
Remove the drivetrain from below the car. Remove the bolt that holds the steering shaft. Unbolt the lower control arms, then swing them out of the way. Take off the front anti-roll bar.
Use a floor jack to support the transmission and an engine hoist to support the engine. Also use a floor jack to support the car somewhere other than the crossmember. The frame rails are effective to use, or consult the owner's manual for recommended jacking points.
Unbolt the crossmembers for the engine and transmission, then lower the driveline until it reaches the floor or a dolly. This section weighs about 540 pounds, so if you are using a dolly, ensure it can support the weight of this section.
Use the engine joist and connect it to the lower radiator core support, then lift the nose of the car high enough that the engine can slide out from underneath the car.
Inspect the engine and replace any stock parts you wish while the car is taken apart. People often install new fuel filters and upgraded fuel pumps at this stage.
Take the front clip off the RB25 engine using the same steps you followed to remove the engine from the 240SX. The front clip is the front bumper, including the clips used to hold it in place.
Remove the belt-driven cooling fan from the front clip, as it will not fit the 240SX. If you wish to replace the clutch on your RB25, now is the best time to do it, while the engine is on the ground.
Use the R33 crossmember to bolt the new engine into the 240SX. You will have to remove some of the hood bracing to clear the throttle body and blow-off valve. Adjust the bracing inside the car to fit the engine.
Run a piece of power steering hose from the rack to the reservoir, or install a real cooler. You can also bend the old aluminum lines until they fit. For best results, use a new cooler. Other methods of installation can fail or cause damage if not done correctly.
Use a pair of billet-aluminum spacers to relocate the holes on the transmission and fit it into place.
Use an engine mount kit to move the engine down and to the back about an inch and a half to make it fit in the right spot. The instructions that come with the engine mount will tell you how to do this.
Slide the drive shaft yoke from the R33 into the drive shaft from the 240SX and shove it all the way forward. Bolt the drive shaft to the differential and leave it hanging.
Measure the distance from the center of the differential where the u-joint is, to the center of the transmission where the u-joint is on the back. Subtract an inch from the measurement to allow for the driveline to move around. Once this is complete, take the car into a shop for all the final adjustments to be made. You cannot do these at home.
Trim the ends of the hoses in your radiator and use 1.75-inch adaptors to fit the R33 hoses and 240SX hoses together. Always keep an eye on your temperature gauge, as a new radiator will be in order over the long term.
Use the mounts on the radiator and car to mount the radiator in place.
Drill holes in the left front fenderwell for intercooler pipes and mounting brackets.
Connect the B-pipe downpipe casting to the catalytic converter by bolting the exhaust right up to the 240SX.
Move the throttle cable mounting bracket closer to the throttle body using a sub-bracket.
Loop the high pressure line around itself and connect it from the power steering pump to the pump in the Nissan. The low pressure line should connect the same way without looping it around itself.
Look over everything on the car and put the final few pieces on. This includes the hood and any remaining pieces. Have a friend look over the car as well. Then start it.
