The RB engine into an S-chassis swap is one of the most popular — and most argued about — builds in the Nissan community. An RB20DET, RB25DET, or RB26DETT dropping into an S13, S14, or S15 gives you a silky inline-six with serious power potential sitting behind a chassis that's already proven itself as one of the best handling platforms ever built.
But it's not a bolt-in job. Here's what you actually need to know before pulling the trigger.
Why People Do This Swap
The S-chassis came from the factory with the SR20DET — a capable, tuneable engine that plenty of serious builds are still running. So why swap? A few reasons come up consistently:
• Power ceiling: The SR20 is a four-cylinder. The RB series is a straight-six, and the RB26DETT in particular has a ceiling that far exceeds what most people will ever need.
• Sound and character: There's a reason the RB engine has a cult following. The intake noise, the power delivery, the way it revs — it's a different driving experience.
• The challenge: Some builds are done simply because it's a difficult, satisfying thing to accomplish well.
The Core Problem: Engine Mounts
The S-chassis was never designed for an RB engine. The engine bay can physically accommodate one, but the mounting points don't line up — which means without the right kit, you're fabricating from scratch or relying on someone else's custom work of unknown quality.
This is where a proper engine mount kit becomes the foundation of the entire build. Get it wrong and you're dealing with drivetrain vibration, clearance issues, and stress on components that aren't designed to handle misaligned forces. Get it right and the rest of the build has a solid base to work from.
Our Clark's Auto RB to S-Chassis Mount Kit is engineered specifically for the RB20DET, RB25DET, and RB26DETT into S13, S14, and S15 platforms. Every dimension has been worked out to put the engine in the right position, with appropriate clearances, without requiring custom fabrication on your end.
What Else Goes Into the Swap
The mount kit is the starting point, not the finish line. A complete RB swap into an S-chassis typically also requires:
• Gearbox: The RB engines use a different bellhousing pattern to the SR. You'll need either an RB-specific gearbox or an adapter. Most builders run the RB25 with a compatible Nissan Skyline or aftermarket transmission.
• Driveshaft: The length and flange will almost certainly need to change. Custom or modified driveshafts are standard practice.
• Cooling: The RB runs hotter than the SR and you'll likely need a larger radiator and appropriate plumbing.
• Engine management: RB engines can run on their factory ECU but most serious builds move to aftermarket management.
• Wiring: This is where most people underestimate the complexity. The RB loom was not designed for the S-chassis. Budget time and skill here. Buy an aftermarket kit.
Which RB for an S-Chassis?
The RB25DET (Series 1 or Series 2 or NEO) is the most popular choice for S14 and S15 builds — good power, widely available, well-supported by the aftermarket. The RB26DETT from the R32/R33/R34 GTR is the prestige option: more powerful, more expensive, and more complex. The RB20DET is lighter and cheaper but offers less power potential.
For an S13, the RB20 and RB25 are both common. The S14 and S15's slightly larger engine bay makes the RB25 and even RB26 more manageable.
Perhaps you want an RB30... well this is a story for another day.
Getting Started
If you're planning an RB swap into an S-chassis, start with quality mounts. It's the one part of the build you don't want to cut corners on — everything else in the build follows from getting that right. Check out our full RB to S-Chassis Mount Kit, available for S13, S14, and S15.