XYZ Racing Circuit Master Coilovers — Maserati BITURBO SI φ52 welding (PCD: 4X98) 1986-1991

The Biturbo SI’s twin-turbo layout put power down through a chassis never designed around modern spring rates, and the factory dampers on a car this age have long since given up matching that engine’s urgency. XYZ Racing’s Circuit Master coilover replaces that ageing setup with a monotube design built specifically around the SI’s φ52 strut welding and 4×98 PCD, so the geometry stays correct while everything else about the ride gets rebuilt from the ground up.

For sustained circuit lap-time work in an eighties Italian turbo car, the priority is repeatable damping under load, not one good lap before the suspension goes soft. Circuit Master is XYZ’s dedicated track-focused platform, and on the Biturbo SI it’s aimed at owners who actually lap these cars rather than trailer them to shows.

What this coilover does for your 1986-1991 Maserati BITURBO SI φ52 WELDING (PCD: 4X98)

With 9720 damping combinations on tap through the Circuit Master’s 3 external knobs, you can separate compression from rebound rather than fighting a single-adjustment compromise – useful on a chassis like the Biturbo SI where front-end grip and rear stability don’t naturally arrive together. Ride height comes down through the coilover sleeve, tightening body control under the SI’s twin-turbo torque delivery and reducing the pitch and squat that stock dampers let through. The monotube construction resists the heat build-up that kills oil-based damping consistency over a full track session, so the third and fourth lap feel like the first. Because the kit is built to the correct φ52 strut diameter and 4×98 hub pattern for this chassis, there’s no adapter or bushing compromise sitting between the damper and the car’s actual geometry.

About the Circuit Master coilover

Circuit Master sits at the top of XYZ’s range as the design built for racing rather than road comfort, developed and run by XYZ’s own racing teams across multiple international circuits rather than just bench-tested. The headline figure is 9720 possible adjustment combinations, delivered through three external knobs that let a driver tune compression and rebound independently to suit a given circuit or tyre. Those knobs use a small-oil-hole metering design, which is precise for fine damping control but means you may hear a faint noise over sharp bumps – that’s the oil moving through the narrow passage as intended, not a fault, and it’s a non-issue on the smooth surfaces this damper is built for. XYZ positions Circuit Master alongside its Drift Spec and Tarmac Rally lines as the option built for drivers chasing lap time rather than daily ride quality, and the internals reflect that: this is a damper built to be pushed hard, repeatedly, rather than driven gently once a week.

Fitment for the Maserati BITURBO SI φ52 WELDING (PCD: 4X98) (1986-1991)

This Circuit Master kit is engineered to the MS03 chassis code covering Maserati Biturbo SI production from 1986 to 1991, matched to the φ52 strut welding diameter and 4×98 PCD hub pattern specific to this variant. Confirm your car sits within this SI-spec welding and bolt pattern before ordering, since Biturbo derivatives varied strut and hub specification across the range.

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Configure your φ52 / 4×98 Circuit Master spec for the Biturbo SI below, and set your starting damping ahead of your next track outing.