Tuning Guide

Ignition timing explained

By Nathan Devonshire

Ignition timing is the most important ignition adjustment — and the most misunderstood. Here is what it actually means, why the spark fires before the piston reaches the top, and how it is set on the Stag.

What timing means — firing before the top

Setting the ignition timing means setting the exact instant the spark fires, measured against the piston’s position — and the spark fires before the piston reaches the top of its stroke, before top dead centre, or BTDC. Why early? Because burning takes time. The mixture burns over a few thousandths of a second; light it just before the top and the pressure peaks just after, right as the piston starts down, pushing hardest at the most useful moment. Fire too late and you waste the push; too early and the rising pressure fights the still‑climbing piston.

Why the timing has to change — advance

The burn takes about the same time whatever the engine is doing, but the piston moves faster as revs rise — so to keep the pressure peaking in the same place you must light the fire earlier, more degrees before top dead centre. That progressive earlier firing is advance. Load matters too: light throttle wants a little more advance, hard load a little less to avoid pinking. This is why the distributor carries its centrifugal and vacuum advance; what you set by hand is the starting point they build on.

Static timing — and the Stag’s quirk

The base setting is the static timing: the degrees BTDC at which the points just open, engine stopped, set by turning the engine to the marked position and rotating the distributor until the points break. The Stag adds a wrinkle worth knowing before you start: its timing is set from cylinder two — the left‑front — not cylinder one as on almost every other engine, a consequence of the V8’s unusual cylinder numbering (see the firing‑order page). You also generally need to remove the coil to reach the timing scale, unless you have the factory tool. The exact figure is in the manual.

Dynamic (strobe) timing — setting it running

The more accurate method uses a strobe timing light, clipped to a plug lead (cylinder two on the Stag), which flashes as that cylinder fires; shine it at the crank pulley and the timing marks appear frozen, showing the actual timing. Run the engine at the specified rpm — usually with the vacuum advance disconnected and plugged — and rotate the distributor until the marks sit where the manual says. Strobe timing catches what static cannot: worn advance and a wandering shaft.

Reading the symptoms

Too retarded — late — gives a flat, gutless engine that runs hot. Too advanced — early — brings pinking under load, a light metallic tinkling as the mixture detonates. On a Stag that heat matters more than most: the V8 runs warm enough already, so timing‑induced pinking and the extra heat it brings are worth catching early. A well‑timed engine pulls cleanly, does not pink on a firm throttle in a high gear, and runs at a sensible temperature — always returning to the manual’s figures as the baseline.

A note on modern fuel

Old timing figures and modern petrol do not always agree — an engine set to a 1970s figure can pink on today’s fuel, and a small adjustment, or the right high‑octane ‘super’, usually sorts it.