Hybrid How-To: Engine Swap

By Dave Coleman
Photography: Dave Coleman

What and Why
Rear-wheel-drive cars just have a natural balance, with even weight distribution, lots of grip, clean steering feel uninfluenced by driveline torque, and of course, the ever-present temptation of powerslides. And if you want rear-wheel drive for cheap, the 240SX is virtually untouchable. As far as picking the RB25 instead of the many other engines that will fit the 240SX, we've got a whole story. Go read it (page 130).

Picking the Chassis
The S14 was sold in relatively pathetic numbers from 1995 to its quiet demise in 1998. In its last two years, a facelift added more aggressive-looking headlights, but other than that, things were basically the same. By far, the most desirable of the S14s is the SE that came with the five-lug hubs that allow countless brake upgrades (see "Project Silvia Part I," Nov. '02) and a viscous limited-slip differential. Option packages were mixed up and confusing during S14 production, so just because you see five-lug wheels, don't assume you have the limited slip. Turn the wheel, mash the pedal and count the stripes.

A five-lug conversion on an S14 is relatively easy if you start with a four-lug car, requiring only new hubs, rather than the hub/spindle /ball joint mess required on the front of an S13. If you don't mind the smell of older cars, the 1989 to 1994 S13 is around 300 pounds lighter (depending on options) and nearly identical mechanically. Most of this swap is the same with an S13.

Picking the Engine
The donor car is an R33 Nissan Skyline GT-S 2.5t. A complete front clip is usually recommended, because the many wiring and plumbing details are easier to work out when the original engine compartment is there for reference. Also, depending on which engine mounts you choose to use, the Skyline front crossmember may be needed.

As a bonus, most front clips come with big, four-piston front brakes which will bolt onto a 240 SX if you have the five-lug hubs (or you can have the rotors redrilled to four-lug). The clip for this swap came from Night Szevyn Racing in Seattle, but was shipped to Ridgecrest, Calif., so we could do the swap in 100-degree heat. After all, it's not work if you aren't suffering.

The earlier, less-expensive R32 Skyline GTS-t engine will also fit, but it's only a 2.0 liter (RB20DET), so the extra weight of a six cylinder seems somewhat pointless if you don't get more displacement.

Engine Removal and Prep Work
If your car has air conditioning, have the system evacuated before removing the engine. Venting freon to the atmosphere is illegal and will give people in Australia sunburns. If you plan on keeping the A/C, it will be easiest to keep the Skyline pump and have the new hoses made to connect the pump to the 240SX air conditioning system. Any A/C shop should be able to handle this by simply crimping new hoses onto the fittings from the Skyline pump.

Next, remove the radiator, remove the entire engine wiring harness from the car, disconnect the fuel lines and unbolt the driveshaft. Your life will be easier if you also remove the hood. Disconnect the heater hoses from the engine and leave them in the car. They'll come pretty close to slipping onto the RB25.

The easiest way to remove the drivetrain is from below, crossmembers and all. To do this, remove the bolt holding the steering shaft U-joint in place, unbolt the lower control arms and swing them out of the way, remove the front anti-roll bar and support the car on something other than the crossmember (the frame rails under the footwells will work). Support the engine with an engine hoist and the transmission with a floor jack.

Now, unbolt the engine and transmission crossmembers from the car, and lower the driveline to the floor. If you have a low-profile furniture dolly, you may want to set the engine on that. Just remember, the KA24 driveline weighs about 540 pounds with crossmembers and steering rack attached.

Hook the engine hoist to the lower radiator core support and lift the nose of the car high enough that you can slide the engine out from below.

Now is a good time to clean the engine compartment and possibly even paint it. Check below the master cylinder for peeling paint and repair it now while you can get to it. This is also the time for new fuel hoses and a new 300ZX fuel filter. You should also consider upgrading the fuel pump. The stock fuel pump, if it's in good shape, may support the stock RB25 for a while, but a tired pump or an increase in boost could be trouble. A Q45 or 300ZX pump will do the job unless you have enormous power goals, in which case, you better be able to figure out fuel pumps on your own.

If you bought an entire front clip, you'll have to pull the RB25 from the clip as well. The belt-driven cooling fan from the Skyline won't fit the smaller 240SX engine compartment, so go ahead and remove it, along with the fan shroud. While you have the engine on the ground, this is a good time to consider replacing the clutch. The R33 Skyline GT-S 2.5t uses a 240-mm clutch with the same critical dimensions as the non-turbo Z32. A stock Z32 clutch will work, though it may be a little weak if you crank the boost. Jim Wolf Technology also has upgraded units that should handle more than 500 lb-ft of torque. The R34 versions of this engine used a pull-type clutch. You're on your own finding replacements for that one.

Mounting the Engine
Now you have to start making decisions.

If you're eating rice and beans just to pay for the engine, you'll be glad to hear it will bolt in using the R33 crossmember and fit well enough to get you on the road, but the engine will sit a little higher and a little farther forward than is ideal. Some of the hood bracing will have to be removed to clear the throttle body and blow-off valve flange and the shifter will sit about an inch and a half forward of the center of the shifter hole in the floor. The cast-iron downpipe will also interfere with the steering shaft, and the transmission crossmember won't quite bolt in properly. The severity of the steering shaft interference varies from car to car, depending on how all the manufacturing tolerances stack up, how worn out the mounts are and how bent the car is. In some cases, you may simply need to notch the downpipe a bit, in others, you may need to fabricate a new one. Just remember, the engine will move around when it's making torque and from cornering loads, so give the steering shaft some room. You don't want the steering locking up in a moment of hard acceleration and cornering.

Both the Skyline and 240SX crossmembers are designed to accept left- or right-hand-drive steering racks, so putting your old rack on the Skyline crossmember is simple. The power steering return line from the 240SX is aluminum and is designed to act as a power steering cooler by running back and forth across the front of the crossmember before returning to the reservoir.

The front of the Skyline crossmember is a different shape, however, and the line won't fit. You have three choices here. Either skip the cooler and run a new piece of power-steering hose from the rack directly to the reservoir (not recommended), install a real cooler, or grab the old aluminum lines with both hands and bend them until they fit. You'll need to add some adell clamps, zip-ties, or bits of bailing wire to hold the lines in place if you take the third option.

The Skyline's transmission crossmember is nearly identical to the one on the 240SX, but the transmission is longer, so it won't line up with the holes in the car. Again, you have options.

If this is just a show car, file the bolt holes on the transmission mount so it can slide forward on the transmission a half inch or so. Then shove on the flimsy, flexy transmission mount until the center hole on each side of the crossmember (originally a drain hole, not a bolt hole, but it will work) lines up with the rearmost mounting hole on the car. Bolt it on with one bolt on each side (it's supposed to have two) and go polish something. Oh, sure, the top of the transmission will be jammed up into the top of the tunnel, but that won't really matter on a show car.

Now, if you actually intend to use that big turbo six to make power, two bolts aren't enough, and having the transmission hitting the tunnel won't do. Lying in a pool of sweat and gear oil assessing the situation with Brian Flynn of Super Tuner Motorsports (who was doing all the heavy lifting on this particular job), we realized both the height and mounting hole shortage could be addressed with a simple pair of billet-aluminum spacers designed to lower the transmission and relocate the holes simultaneously. He's going to make the spacers, we're going to tell you where to get them: www.supertunermotorsports.com. There, we've done our part.

Finally, if you want the engine to sit low enough to clear the hood bracing, the shifter to sit where it used to, the steering shaft not to hit the downpipe and everything to bolt in properly, there's a third option. McKinney Motorsports in San Diego, Calif., unStable Hybrids in Conyers, Ga., and by the time you read this, probably Super Tuner Motorsports in Ridgecrest, Calif., all make engine mount kits that move the engine down and back about an inch and a half. In addition to making everything fit better, moving the drivetrain, which weighs about 650 pounds, shifts the center of gravity in exactly the right direction. This is also the ideal option if you have an engine, transmission, harness and ECU, but no front clip.

The RB25's transmission is slightly longer, and the output shaft slightly larger than the 240SX, so a new driveshaft is needed. If the Skyline's driveshaft yoke was included in your clip, slide it into the transmission and shove it all the way forward. Then bolt the stock driveshaft to the differential and let it hang. Measure the distance from the center of the U-joint on the diff to the center of the U-joint on the back of the transmission and--this part is important--subtract 1 inch to allow for driveline movement. Take all the pieces to a driveline shop and tell them "I want this yoke (Skyline) and this rear U-joint (240SX) on a one-piece driveshaft this long (your measurement)." Then give them money (probably a few hundred bucks). If you don't have the Skyline yoke, you can use one from a twin-turbo Z.

If you try to shorten the stock two-piece driveshaft instead of making a new one-piece, it might work. Or the angle of the short front section of the driveshaft may get too steep, leading to a driveshaft failure. It's your choice. If you're using McKinney's mounts, the shop also offers a shortened one-piece driveshaft with larger U-joints that's ready to install.

An RB20DET uses the same size driveshaft yoke as the 240 SX, and is reported to accept the KA24 driveshaft without modification.

The stock 240SX radiator has nearly the same hose locations as the Skyline radiator, though the KA24DE uses a smaller hose than the RB25DET. Making it fit can be as simple as trimming a little from the ends of the Skyline hoses and using an adaptor to fit the 1.75-inch Skyline hose to the 1.75-inch 240SX radiator. Keep an eye on the temperature gauge, as the 240SX radiator was never intended for the thermal load a Skyline engine will put on it. In the long run, an upgrade, such as the Koyo aluminum radiator in our Project Silvia, may be in order.

If you got a front clip with an undamaged radiator, the much larger R33 radiator, according to unStable Hybrids, will just squeeze under the stock 240SX hood.

Depending on your mounting choice, the belt-driven fan may not fit, so you'll have to switch to electric fans. The Flex-a-lite Twin Line 320 dual 10-inch fans we used on our Project Silvia (June 2003) have been working well and would be a good choice for this application as well.

The S14 heater hoses are also a nearly perfect fit, sliding onto the RB25DET with only minor trimming.

The stock intercooler is a relatively small side-mount. Inlet and outlet plumbing is through the left front fenderwell. Holes will have to be drilled for the intercooler pipes and for the intercooler mounting bracket. This is not a direct bolt-on, but it's close. Of course, a front-mount is probably in the plans, so you could always just skip ahead to that.

There are only two potential issues with the exhaust. First, the aforementioned clearance issues between the steering shaft and the downpipe casting. If this is a serious issue on your car, you may have to make a new downpipe.

Super Tuner Motorsports is also making one, so you can buy it from them. If the B-pipe that connects the downpipe casting to the catalytic converter came with your engine (sometimes it comes on front clips, sometimes it doesn't), it should bolt right up to the 240SX exhaust. You'll want a bigger exhaust, of course, but at least it won't have to be custom made. If this B-pipe is missing, Night7 offers a 3-inch B-pipe for about $250.

The throttle cable is long enough to reach the RB25DET throttle body, but it has less free cable at the end than the Skyline cable did. This can be remedied by moving the throttle cable mounting bracket closer to the throttle body with a simple sub-bracket.

Assuming you've already dealt with the power steering cooler on the return line, there are only two more power steering lines to deal with. Both the high- and low-pressure lines from the KA24 power steering pump will bolt onto the Skyline pump. The high-pressure line will have to loop around on itself a bit, but just tell people it's a vibration isolation loop and they'll leave you alone.

If the Skyline crossmember and engine mounts are used, you should also be prepared for interference between the front anti-roll bar and the oil pan. Small (3/4 to 1 inch) spacer blocks between the bar's pivot bushings and the frame rails should solve the problem.

You know all those wires in the Skyline clip? Get them. What you do with them depends on your comfort level with electrons. If you want the cleanest harness possible, send the Skyline and 240SX harnesses to McKinney Motorsports or unStable Hybrids, and they'll splice the two together, eliminating anything unnecessary and returning a working harness. If you don't have a harness at all, call McKinney and start crying. McKinney is working with Jim Wolf Technology to run the RB25DET on the VG30DETT ECU from a twin-turbo Z and a modified Z harness. As of this writing, that project is unfinished, but maybe your tears will motivate them to finish.

If you hate electrons and just want everything to work as quickly as possible, Night Szevyn Racing suggests removing your dash and transferring both the engine and dash harnesses from the Skyline. You can lay the Skyline dash harness right over the 240SX harness and power them both up with the ignition switch. The terminals on the back of the switch are all labeled with letters, just make sure the five ignition switch wires on the Skyline harness go to the same letters they originally went to.

This method will force you to use the Skyline instrument cluster, which sort of fits. It isn't really the right shape, and none of the mounting bolt holes actually line up, but it kinda wedges into the space allotted. Running two parallel dash wiring harnesses will leave you with a lot of extra wires and plugs, but at least it won't take much time.

The Moment of Truth
This is when you think back to the last time you drove your KA24-powered 240 and wonder if you used premium fuel. You'll need it now. While you're thinking about that, call every car friend you have and get them to look at your installation and find your mistakes before you start the car.

Fire it up and go look for Supras.

Swap Basics
Chassis: Second-generation (S14) Nissan 240SX
It's rear-wheel drive; what else do you need? OK, how about relatively inexpensive (or dirt cheap if you use the older S13 chassis), surprisingly durable, excellent handling and extensive parts interchangeability with an incredible list of cars. Just look at the parts donors: the earlier 240SX; '88 to '02 Silvias; the Z32 300ZX; R32, R33 and R34 Skylines; Infiniti J30 and Q45; and a few obscure JDM sedans we can't even think of. The S13 and S14 are probably Japan's most popular sports cars, so every Japanese tuner makes parts for them.

Engine: RB25DET
It's from a Skyline, what else do you need to know? OK, how about an indestructible short-stroke, iron-block six with one turbo and lots of potential. The rear-drive Skyline GT-S 2.5t was far more common than the all-powerful and all-expensive GT-R, so front clips are fairly abundant in Japanese junkyards. As importers discover this swap, the supply of engines in the United States should be good.

Including the transmission, the Skyline drivetrain is about 180 pounds heavier than the 240SX drivetrain you're removing. Consider the effect this will have on performance of any kind. How clean this swap is depends entirely on how much you want to spend. It's a bolt-in if you're willing to call pressure-treated pine an "organic carbon-fiber transmission mount," or it could require custom mounts and a complex hybrid wiring harness if you want everything to be perfect. There are, thankfully, many levels of middle ground.


Leave the heater hoses in the engine compartment when removing the KA24. They fit the RB25 with only minor trimming.
Be prepared to accept more weight with the RB25DET. Fully dressed with both crossmembers and the steering rack attached (but no A/C), the KA24DE weighs about 540 pounds. With two more cylinders, a much beefier transmission and a turbocharger, the RB25DET weighs about 720 pounds. That's an extra 180 pounds to accelerate, stop and turn. Good thing it makes more power.
The 240SX crossmember (bottom) places the engine mounts near the rear of the crossmember. The R33 Skyline crossmember puts them on extensions hanging off the front. Note also that the steering racks are reversed and the power steering lines are far from interchangeable.
With the steering rack removed, the rack mounts on both sides are identical, making it easy to change from a right-hand- to a left-hand-drive steering rack.
The lower control arm mounts in the groove in the center of the crossmember. Before swapping, we checked that both crossmembers mounted the arm in the same place.
With the steering rack swapped and about five minutes of monkey-bending the power steering lines by hand, we were able to get the power steering cooler to fit the Skyline crossmember. A longer hose connecting the rack to the cooler line will be needed.
The steering U-joint and the downpipe are friendly if you use the R33 crossmember. Your options are to notch the downpipe, which may or may not work, make a custom downpipe, buy a downpipe from Super Tuner Motorsports, have unStable Hybrids make a new downpipe starting with your casting, or use the McKinney Motorsports mounts. If you do notch the stock downpipe, be sure to leave plenty of space, as the engine will move, and your steering is important.This is a good time to check the condition of the U-joint. Ours was sticky and notchy in its movement. The joint will be seeing a lot of heat from the downpipe, so a fresh joint is good preventative maintenance anyway.
With the engine mounted on the crossmember and the car high in the air, it's a simple matter of calling all your friends and neighbors over to shove your 720-pound drivetrain across the floor so you can lift it up into the engine compartment.
Lifting the engine into the car, it's easy to crush countless wires and hoses. Be careful.
The transmission crossmember doesn't exactly line up. By slotting holes and accepting contact between the transmission and the tunnel, you can get one bolt to fit each side. For better fitment, you can use Super Tuner Motorsports' adaptor blocks, or for a perfect fit, start over with new mounts from them, or from unStable Hybrids or McKinney Motorsports.
If you use the Skyline harness, it'll have to be rearranged somewhat to put the ECU on the passenger's side. After the rerouting, three wires will have a hard time reaching their destinations. The mass airflow sensor wire, on the left, must be lengthened (be sure to use shielded wire anywhere it's used in the stock harness), the O2-sensor wire (center) must either be rerouted or lengthened, and the boost controller wire can either be lengthened, or the vacuum hoses on the boost controller can be lengthened to reach the connector.
If you want to use the Skyline's dash harness in parallel with the 240SX harness, you'll end up using the Skyline instrument cluster. It's not quite the same size as the 240 cluster, it won't bolt in, but it will fit in the hole and is a tight enough fit not to rattle around much.
Using the stock side-mount intercooler will require some minor drilling in the fender well for intercooler pipe and mounting bracket installation.
The Skyline's driveshaft yoke (right) is much larger than the 240SX, so you'll need to use the Skyline part when making your custom driveshaft. If you don't have one, a twin-turbo 300ZX driveshaft yoke will work.
Japanese battery posts are very small. If you plan to use the Japanese alternator and starter harness, you'll need to switch the battery terminal.
The 240SX fusebox gets alternator power from this post. You'll need to cut the connector off the Skyline's two big alternator power wires and replace it with a post-style terminal.
To check hood clearance, we put duct tape sticky side up on the two highest points of the engine (the throttle body and blow-off valve flange) and closed the hood. Where the tape stuck, we had a problem.
With the hood bracing trimmed like this, there are no more clearance problems.
There isn't enough free cable at the end of the 240SX throttle cable. A simple extension to move the mounting bracket closer to the throttle body will solve the problem.
Using the R33 crossmember, the shifter will sit about an inch and a half farther forward than the stock one did.

Information Source: www.sportcompactcarweb.com