Rebuilding the FC3S Right: A 13B-T Drivetrain Build Guide
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The FC3S doesn't get the same spotlight as its FD successor, but anyone who's driven a well-built second-gen RX-7 knows the truth: this chassis is special. Lighter than the FD, raw in all the right ways, and with a 13B-T or 13B-RE under the hood that responds beautifully to the right parts. This post walks through a recent FC3S drivetrain build we completed at DLW Motorsports — the diagnosis, the parts selection, the install notes, and the result.
The Car: A 1987 FC3S Turbo II
The owner of DLW Motorsports brought in a 1987 RX-7 Turbo II — a 13B-T car with a 5-speed manual and a history of spirited street driving. The clutch had been slipping for months, the flywheel was original, and the owner wanted to use the refresh as an opportunity to build the drivetrain for more power down the road. The goal: a street-friendly setup that could handle 350–400whp without drama — with a clear path to 500whp down the road.
This is exactly the kind of project the FC rewards. Get the foundation right and the rest of the build falls into place.
Step 1: Drivetrain Inspection
First thing on the lift: a full drivetrain inspection. The stock clutch disc showed significant wear and glazing — classic signs of a clutch that's been slipping under boost for too long. The pressure plate was still within spec, but we never reuse a pressure plate on a performance refresh. The flywheel had surface scoring and minor heat discoloration on the friction face.
Lesson #1: On a turbocharged rotary, a slipping clutch is a compounding problem. The heat it generates cycles into the flywheel, the transmission input shaft bearing, and even the rear main seal. Catch it early.
Step 2: Clutch Selection for the 13B-T
The 13B-T in the Turbo II is a torquier, more aggressive engine than the naturally aspirated variants — and clutch selection needs to reflect that. For a street build targeting 350–400whp, you need something that can hold the power without making the car miserable in traffic.
For this build, we went with the Stage 3 Clutch Kit (1MS) for Mazda RX-7 Turbo II (13B-T). It hits the sweet spot for this power range — higher clamp load than a street clutch, still very manageable in daily traffic, and built to handle the power levels most FC builds are targeting. The 1MS is our go-to recommendation for 13B-T builds in the 300–400whp range.
For lighter street builds that won't push past 300whp, the Ironman Sprung (Street) Clutch Kit for Mazda RX-7 Turbo II (13B-T) is a great option — softer engagement, very street-friendly, and ideal for a more relaxed build.
For the serious builds — 450whp and up, or dedicated track use — the 7.25in Twin Disc Race Kit for Mazda RX-7 Turbo II (13B-T) is the right tool. It includes a steel flywheel and is built for sustained high-load use.
Here's how we stage clutch selection for the 13B-T:
| Power Level | Recommended Clutch |
|---|---|
| Stock – 300whp | Ironman Sprung (Street) |
| 300 – 400whp | Stage 3 (1MS) |
| 400 – 500whp | Stage 5 (2MS) |
| 500whp+ / Track | Twin or Triple Disc Race Kit |
Step 3: Flywheel — Keeping It Light on the FC
The FC3S stock flywheel is heavy — heavier than most people realize. Swapping it out is one of the highest-impact, lowest-risk upgrades you can make during a clutch refresh. The difference in throttle response is immediately noticeable.
For this build, we went with the Chromoly Lightweight Flywheel for Mazda RX-7 Turbo II (13B-T) (without counterweight). Here's why chromoly over aluminum for this application:
- The owner planned to push power levels over time — chromoly handles heat cycles and high-torque loads better than aluminum at elevated power
- Still significantly lighter than stock, with a meaningful improvement in rev response
- More durable for a car that sees mixed street and occasional hard use
If you're building a lighter, lower-power street car and want maximum rev response, the Aluminum Lightweight Flywheel for Mazda RX-7 Turbo II (13B-T) is the better pick. Lighter, faster-revving, and ideal for builds that aren't chasing big power numbers.
Step 4: The Power Adder — Series 4-5 FC3S 500HP Kit
With the drivetrain foundation sorted, the next conversation was about power. The owner's target was 500whp — enough to make the FC genuinely fast without sacrificing street manners. For that, we spec'd the Series 4-5 RX7 FC3S 500HP Kit.
This kit is purpose-built for the FC3S platform and takes the guesswork out of building to 500whp. Rather than piecing together individual turbo components and hoping everything plays nicely together, the 500HP Kit is a cohesive system — engineered to work as a package on the 13B-T.
A few reasons this kit makes sense for a build like this:
- Matched components — no compatibility guesswork between turbo, manifold, and supporting hardware
- Clear power target — designed and validated for 500whp, so you know what you're building toward
- FC3S-specific fitment — built for the Series 4 and 5 chassis, not adapted from another platform
Pairing this kit with the Stage 3 clutch and chromoly flywheel gives the drivetrain the capacity to handle the power increase without being the weak link in the build.
Step 5: Installation Notes — FC-Specific Details
A few things that come up specifically on FC3S drivetrain work:
Rear main seal. The FC's rear main seal is notorious for weeping on high-mileage cars. With the transmission out, this is a 20-minute job that can save you a full re-pull later. Do it every time.
Transmission input shaft bearing. Inspect it while you're in there. A worn input shaft bearing causes clutch chatter and can accelerate disc wear. Replacement is cheap; ignoring it is not.
Flywheel bolt torque. Use new bolts, follow the torque spec, and use thread locker. The 13B-T's power pulses are hard on hardware that isn't properly secured.
Clutch break-in. No aggressive launches for the first 500 miles. Let the friction material seat against the flywheel properly. A clutch that isn't broken in correctly will never perform to its full potential — and it will wear faster.
Pilot bearing. Replace it. No exceptions.
The Result
After the install and a proper break-in, the FC came back to life. Clutch engagement is clean and predictable across the RPM range. The chromoly flywheel gives the 13B-T a noticeably sharper throttle response without sacrificing the drivability the owner needed for street use. The car pulls hard through all gears with zero slip — and the drivetrain is now ready for the 500HP Kit when it goes on.
This is what a proper build sequence looks like. Foundation first, power second. Everything in its right order.
Parts Used in This Build
- Stage 3 Clutch Kit (1MS) — RX-7 Turbo II (13B-T)
- Chromoly Lightweight Flywheel — RX-7 Turbo II (13B-T), without counterweight
- Series 4-5 RX7 FC3S 500HP Kit
Building Your FC3S?
Whether you're refreshing a tired drivetrain or building for serious power, we carry the full range of clutch, flywheel, and turbo options for every FC3S variant — 13B-RE, 13B-T, and everything in between. Browse our FC3S parts catalog or reach out directly — we're happy to help you spec the right setup for your build.