Cadillac 331 V8 Pro Series Ready to Run Distributor

• Fits Cadillac 331 CID V8 — 1949–1955 carbureted applications only

• Counter-clockwise rotation — verify plug wire routing before installation

• External coil required (35,000V+) — no ignition box needed, tach output included

• 12-volt system required — many 1949–1955 Cadillacs need 12V conversion before use

The TSP Pro Series Ready-to-Run Distributor for the Cadillac 331 V8 is a precision ignition upgrade for carbureted 331 CID (5.4L) Cadillac applications from the 1949 through 1955 model years. Built on a machined aluminum housing with a circuit board module and magnetic pickup trigger, this distributor provides accurate, repeatable ignition timing without the need for points, condenser, or a separate ignition control box.

Before ordering — 12-volt electrical system required. The Cadillac 331 was produced during an era when many vehicles left the factory equipped with 6-volt electrical systems. This distributor requires a 12-volt electrical system with a charging alternator and is not compatible with 6-volt systems, generators, or ballast resistors. If your Cadillac 331 vehicle has not been converted to a 12-volt alternator system, this distributor cannot be installed until that conversion is completed.

Counter-clockwise distributor rotation. The Cadillac 331 V8 runs counter-clockwise distributor rotation — the opposite of many domestic V8 engines. This affects rotor phasing and spark plug wire routing and must be accounted for during installation. Do not assume standard clockwise plug wire layout applies. Verify your firing order and wire routing for counter-clockwise operation before finalizing installation. Note that later Cadillac V8 engines — the 472 and 500 CID introduced in 1968 — run clockwise rotation. If you are working with a post-1967 Cadillac, a different TSP distributor is required.

The Pro Series design uses an external ignition coil, giving you flexibility to run a coil matched to your build level. A minimum coil output of 35,000 volts is required — coil is not included. Three advance bushings and four advance springs are included, allowing the mechanical advance curve to be tuned for your specific engine combination. A vacuum advance block-off plate and tachometer output extension cable are also included.

The Cadillac 331 V8 — Production Era and What Buyers Need to Know Before Ordering
The Cadillac 331 CID (5.4L) V8 was introduced in 1949 as Cadillac's first modern overhead valve V8 and remained in production through 1955, powering the Series 62, Series 75, Fleetwood, Fleetwood 60 Special, Coupe de Ville, and the limited-production Eldorado. It is a foundational engine in American automotive history and remains an active restoration and custom build platform. Two things define this distributor purchase above all others for the 331 era: the 12-volt electrical system requirement and the counter-clockwise rotation.

12-Volt Conversion — Verify Before Ordering
Many 1949–1955 Cadillac vehicles left the factory equipped with a 6-volt electrical system. This Pro Series distributor requires a 12-volt system with a charging alternator. It is not compatible with 6-volt systems, generators, or ballast resistors. If your vehicle has not been converted to 12-volt, that conversion must be completed before this distributor can be installed. Verify your vehicle's electrical system before ordering.

Counter-Clockwise Rotation — Installation Critical
The Cadillac 331 runs counter-clockwise distributor rotation. When installing this distributor, verify your rotor direction and spark plug wire routing for counter-clockwise operation. Do not use clockwise wire routing assumptions — incorrect plug lead installation based on clockwise rotation will cause misfires across multiple cylinders.

Performance Benefit
The circuit board module and magnetic pickup trigger deliver precise, repeatable spark timing without the wear and drift that accumulates in aging points-based systems — a meaningful improvement on 70-plus-year-old ignition hardware. Three advance bushings and four advance springs allow full adjustment of the mechanical advance curve, which is particularly valuable on modified 331 builds running aftermarket camshafts or performance carburetors. A vacuum advance block-off plate is included for performance applications. A tachometer output extension cable simplifies aftermarket tach wiring.

What engine and years does this distributor fit?
This distributor is confirmed for the Cadillac 331 CID (5.4L) V8 in carbureted applications from 1949 through 1955. Supported vehicles include the Cadillac Series 62, Coupe de Ville, Fleetwood, Fleetwood 60 Special, Series 75 Limousine, Eldorado (1953–1955), and Commercial Chassis. For 1956–1958 Cadillac 365 CID or 1959–1963 Cadillac 390 CID applications, contact TSP directly to verify compatibility before ordering.

My 1949–1955 Cadillac has a 6-volt electrical system — will this distributor work?
No. This distributor requires a 12-volt electrical system with a charging alternator. Many 1949–1955 Cadillac vehicles were factory-equipped with 6-volt electrical systems. The distributor cannot be installed until the vehicle has been fully converted to a 12-volt system with a charging alternator. Verify your vehicle's electrical system before ordering.

The Cadillac 331 runs counter-clockwise rotation — does this distributor account for that?
Yes. This distributor is designed specifically for the Cadillac 331's counter-clockwise distributor rotation. During installation, verify your rotor direction and spark plug wire routing for counter-clockwise operation. Do not assume clockwise wire routing, as wiring the plug leads using a clockwise assumption will cause misfires across multiple cylinders. Note that later Cadillac V8 engines (472/500 introduced in 1968) run clockwise rotation and require a completely different distributor.

Will this fit a 1956–1958 Cadillac 365 or a 1959–1963 Cadillac 390?
The 365 and 390 are evolutionary developments of the 331 architecture and may share distributor compatibility, but fitment for these displacements has not been confirmed in the published specification for this distributor. Contact TSP directly to verify compatibility for 365 and 390 applications before ordering.

Will this fit a 1966–1967 Cadillac with a 429 V8?
No. The 1966–1967 Cadillac 429 uses a separate, dedicated distributor—the TSP 1966–1967 Cadillac 429 Pro Series Ready-to-Run distributor. The 429 is a different engine generation from the 331 and requires its own application-specific unit.

Will this fit a 1968 or later Cadillac?
No. Cadillac introduced the all-new 472 CID V8 in 1968, which is a different engine family that also runs clockwise rotation—the opposite of the 331's counter-clockwise. For 1968 and later Cadillac applications, the TSP Cadillac 472/500 Pro Series Ready-to-Run distributor is the correct unit.

Does this distributor include a coil?
No. This is a Ready-to-Run design that requires an external ignition coil rated at 35,000 volts or higher. The coil is not included and must be sourced separately.

Do I need an external ignition box or CDI unit?
No. The internal ignition module handles all ignition control. No external ignition box, CDI unit, points, or condenser is required.

What is included with this distributor?
This distributor ships with three advance bushings and four advance springs for mechanical advance curve tuning, a color-matched spark plug wire retainer with screws, a vacuum advance block-off plate in black, a power extension cable, and a tachometer output extension cable.

Can I tune the advance curve on this distributor?
Yes. Three advance bushings and four advance springs are included, allowing adjustment of how quickly mechanical advance comes in with rising RPM. For modified 331 builds running aftermarket camshafts, elevated compression, or performance carburetors, a properly calibrated advance curve meaningfully improves power delivery and part-throttle drivability compared to a fixed factory advance setup.

What type of distributor gear is included?
This distributor includes a steel distributor gear. The gear is most compatible with cast iron hydraulic or solid flat tappet camshafts. For roller camshaft applications, consult your camshaft manufacturer for the recommended gear material before installation.

Do I need to set ignition timing after installing this distributor?
Yes. Base ignition timing must be set with a timing light after installation. For most carbureted Cadillac 331 applications, a starting point of 8–10 degrees BTDC at idle is a common reference, though the optimal setting will vary based on your compression ratio, camshaft profile, advance curve setup, and carburetor tune.