S13 RB swap guide

In this guide, we will walk through the process of swapping a Nissan Skyline RB engine into an S13. The RB is a great engine swap choice if you want something different than your standard SR20 swap. The RB has serious power potential, produces more torque, and is arguably the best inline 6 engine ever produced.

Step 1: Decide which RB to swap into your S13

So before we start the swap process, we need to decide on the specific RB variant that we want to use. There are 4 options to choose from

RB20
This is the easiest RB swap to perform and by far the most budget-friendly option. The RB20 might lack a bit of torque but it makes it up with its ability to rev to the moon. The RB20 is quite happy to bang against the rev limiter all day. Something that can’t always be said about other engine swap options.

The RB20 has a much shorter stroke and a lower deck height. The RB20 also has thicker cylinder walls and rumors have it that the RB20 is made with superior metal compared to the RB25. Some tests have shown that some RB20 blocks have the same metallurgic qualities as RB26 engines.

The RB20 does however have some shortcomings. It’s a rather asthmatic engine. It doesn’t breathe well and it has trouble spooling up bigger turbos without introducing a ton of turbo lag. It also doesn’t make a lot of torque which makes the turbo lag problem even worse. This engine loves high RPMs.

RB25
The RB25 has a couple of things going for it. It has more torque than the RB20, and can spool bigger turbos with ease. The RB25 is a strong engine, and making tons of power is typically not an issue for the RB25.

For high-power goals that don’t break the bank like an RB26 would, the RB25 is a great option. It also comes with a significantly stronger transmission than the RB20 which means that running more power doesn’t immediately require expensive gearbox swaps.

When swapping an RB25 you will run into a bit more issues than you would with the RB20. The block is taller which means (depending on the mounts) you might run into clearance issues with the hood. The RB25 transmission is also much bulkier than the RB20 meaning you will have to clearance your transmission tunnel. The RB25 is also more expensive to purchase and requires more swap parts which increase the cost of the RB25 swap.

RB26
This is the ultimate RB swap everybody dreams of. There are not a lot of RB26 swapped S13’s out there and that is with good reason. In theory, the RB26 shouldn’t be that difficult to swap, but it is anything but a bolt-on affair.

The clearance issues with an RB26 are the smallest problems. In terms of size, the RB26 is very similar to the RB25 and thus produces the same issues. The real problem with the RB26 is its all-wheel drive drivetrain. The oil sump of the RB26 has the AWD system built into it. The transmission is massive and can not be converted to rear-wheel drive. This means that the only feasible way to swap an RB26 is to also swap the transmission. Rb26 swap kits and parts are not readily available so you will have to figure out a lot of this on your own.

The astronomical purchase price and the many engineering challenges make the RB26 a very expensive swap.

In this guide, we will focus on the RB20 and RB25.

Step 2: Rip out your old engine

This step is pretty straightforward and I won’t go into too much detail about how to do this. I assume that if you want to perform an engine swap yourself, you know how to remove your old engine.

When removing your old engine, try not to cut any wires and hoses as you might need them later on. You will need to remove the engine, transmission, driveshaft, engine loom, radiator, intercooler, and the ECU. I generally recommend stripping the entire front of your car, meaning, the hood, front bumper, and side skirts. This makes it easier to work around your car and reduces the chance of body panels getting damaged.

Step 3: Fit your RB in your S13

Alright so your engine bay is empty and you are ready to test fit your RB. To mount the RB in an S13 there are a couple of engine mount options. Let’s take a look at our options.

Engine mounts and subframes
Both the RB20 and RB25 are pretty easy to fit. You can either use your stock subframe in combination with a swap mount kit, or you can use a Skyline R32/R33 subframe for a perfect OEM look. Using a Skyline subframe has the advantage that you can retain OEM engine mounts. The second option is to use conversion mounts. These mounts function as a spacer to space the actual rubber mounts further forward. This design is inherently weaker than the Skyline subframe option. I would personally recommend using a Skyline subframe, but I understand these can be hard to source.

Mounting the transmission is rather straightforward. For the RB20 you can use the factory KA24 or CA18 transmission mount. For the RB25 you will require a swap bracket for the transmission and you will need to clearance your transmission tunnel.

Step 4: Fitting the accessories

Fitting the RB into the engine bay wasn’t so hard right? Now its time to fit the accessories to make the engine run. In case you stripped your engine to a short block, now is the time to build it up again. Attach the inlet manifold, exhaust manifold, alternator, power steering pump, etc. Everything that your car would need to run. All of these things should fit without any problem in the S13 engine bay.

When it comes to installing an intercooler I would recommend sourcing a quality front-mount intercooler. You will have to make custom intercooler piping to make it all work. There are some RB swap intercooler piping kits out there but they are generally of low quality and often don’t fit very well. The best route is to get customer piping made. The RB engines have a crossover pipe that a lot of people find ugly to look at. If you are worried about this crossover pipe limiting your power goals, fear not. The crossover pipe can easily handle 450+ horsepower. If you prefer a cleaner look, then a forward facing plenum will be required.

Fitting the radiator
The RB engines have different size inlets and outlets and a different location than your stock radiator. Inline 6 engines are also known to run hotter than a 4-cylinder so it is highly recommended to upgrade to an aluminum aftermarket radiator. A radiator made for the S13 will usually work but you might have to get creative with coolant hose routing.

Another option is to buy an R32 radiator. These are a straight fit into an S13 and have the inlets and outlets in the right place and are of course the right size. The clearance between the engine and the radiator will be minimal, but trimming the RB radiator hoses should work. The RB20 has a sort of coolant neck that gets really close to the radiator and is at an odd angle. It is a bit of a struggle but the upper RB hose will fit if you trim it in the right place.

The factory clutch fan will not fit! You will need to switch to electric fans, most likely a pusher setup. You can use a pull setup but this requires cutting into your radiator support so that you can tilt your radiator forward. If you don’t tilt your radiator you will have to place the fans in front of the radiator and have them push air through. A push setup is significantly less effective than a pull setup. If you go for a push setup I would make sure that you have a high-quality dual-pass radiator and strong high-quality fans.

Power steering
Your S13 power steering lines won’t work for the RB swap. You will need to get a custom high-pressure line made or purchase a power steering line made for the swap. Nubis produces a hose that will fit, but I found it to be a smidge too long. I think custom-made is the way to go. Any hydraulics shop can probably help you out with this for cheap.

Turbo outlet
This is the last thing on the list of accessories that require a custom solution. When using a stock exhaust manifold you will run into clearance issues with the O2 housing/turbo dump. The standard (or any aftermarket) turbo dump/O2 housing is very likely to interfere with the steering shaft on any LHD S13 (depending on the engine mounts used). You can get a custom outlet fabricated, or you can purchase an O2 housing from ISR that is specifically made for this swap. I used the ISR o2 housing and I am quite happy with it.

Step 5: Wiring your RB into your S13

There are 3 options when wiring in your RB. You can either buy a premade swap harness, splice the RB loom into the S13 loom, or completely redo the wiring from scratch.

I would highly recommend you buy a custom swap loom from the likes of Wiring specialties. In theory, doing the wiring work yourself is not that hard, but going with a swap loom will save you so much time and frustration. On top of that, it is also very likely to look a lot better than your own wiring work (unless you know what you are doing of course, in which case go ahead).

Wiring specialties will make a loom that is 100% plug-and-play. They can also customize the loom to your specific, ECU, injectors, etc.

Making your wiring loom from scratch most likely means that you are also getting a standalone ECU. Most ECUs have good documentation on how to wire up your car and there are plenty of other guides online on how to do this. The RB is a relatively simple engine so it shouldn’t be that hard.

The most cost-effective solution is to use the factory engine loom from the RB. To get your RB running you only need to connect a couple of wires. The RB doesn’t rely on any safeties coming from the chassis harness so all it needs is a trigger signal and a connection to the fuel pump.

You can directly swap your old S13 lower engine harness onto the RB. all the plugs should be the same and this means that this part of the wiring loom will directly plug into the chassis loom. To make your dash work you will also need to connect some wires under the dashboard. I intend to write a complete wiring guide once I have it all documented.

Step 6: Getting your car driving again

The final step is to get your car driving again. The final puzzle piece that has been missing is the driveshaft. In case of the RB25 you will need a custom driveshaft as neither the RB nor the S13 driveshaft will fit. For the RB20 you might be able to use your S13 driveshaft. There is a difference between ABS and non-ABS driveshafts, as well as a difference between automatic and manual driveshafts. If you had a manual S13 and you keep the same differential that was in the car, your stock S13 driveshaft will most likely fit. If you are located in the USA you are lucky because there are plenty of companies in the USA that will sell you a brand new driveshaft made for this swap.

Step 7: Final check and test drive

By now your car should be running. It is now time to do a final check. Make sure that all nuts and bolts are properly fastened. Check all your fluids and let the engine get up to operating temperature, make sure it holds steady.

If everything is fastened and holds a steady temperature, then it is time to go for a test drive. Start slowly and get some confidence in the build. Make sure to check up on loose bolts and fluids after every drive.

S13 RB swap conclusions

The RB is a great contender for an S13 engine swap. It keeps it in the Nissan family, fits great, has good power potential, and has an amazing sound.

If you haven’t already tuned your RB, enjoy it in its (near) stock form for a while. See what you like and dislike about it and then start upgrading and tuning it. The RB engines are a fantastic tuning platform with amazing aftermarket support. There is no upgrade that hasn’t been done before.

Both the RB20 and the RB25 are relatively straightforward swaps. Out of the two, the RB20 is the easier swap that is happy in high rev ranges. The RB25 is a bit more complicated but has much higher power potential.