The humble SR four-banger is perhaps one of the most popular engine swaps worldwide, with it seen adorning more engine bays than we have room to list here. Favoured for its bang-for-buck performance and reliability, non-turbo (DE) and turbo (DET) can be had for chump change, and the boosted example has been proven to be easily squeezed to 250kW with simple upgrades. But, when it comes to Mazda chassis, SR swaps are still relatively uncharted waters. Alex Browne from Christchurch saw online that people were using the RX-8 gearboxes behind SR20s as upgrades from the factory units, and thought to himself, why not just put the SR20 into an RX-8? And that’s what he did.
The SR isn’t huge dimensionally — measuring in an almost square 630mm long, 600mm wide (with hot and cold sides), and 600mm tall — making for a semi-hassle-free installation into the RX-8’s deep and long engine bay. To achieve a level fit at the height that he desired, Alex opted to relocate the alternator to the opposite side of the block; however, due to the front-sumped configuration, the cross member had to be modified heavily for clearance. “I’ve done a few engine swaps now, and it was nothing too different from the others. All I had to do was remake the cross member, which I’ve used 60mm tube to connect what was left of the original unit after cutting room for the sump to sit,” says Alex.
What was left of the original cross member formed the basis of the new engine mounts, a custom perch made from 6mm steel plate that would accept the factory SR mounts. The steering rack’s mounting points were also moved forward with the tube section to allow room for the pulleys.
And, like the gearbox swaps that he had initially seen on the internet, the factory RX-8 drivetrain has been retained, with an SR bellhousing and a thrust-bearing spacer to mate the five-speed to the back of the motor. This meant that nothing had to be chopped or fabricated outside of the engine bay.
Overall, Alex tells us that he rates the conversion a good seven out of 10, commenting: “The steering is a little twitching, and the motor is a bit higher than the Renesis, but it makes good usable power, is a relatively straight-forward conversion, and is a tad more reliable.”
SR20DET ORIGIN CHASSIS: Nissan Silvia (S15) CAPACITY: 1998cc CONFIGURATION: Straight-four turbo BORE/STROKE: 86mm x 86mm COMPRESSION: 8.5:1 FACTORY POWER: 151kW / 275Nm WEIGHT: 149kg NOTES: T-25G turbo,