Spark plug gap 1978 ford 351?

The recommended spark plug gap for a 1978 Ford 351 engine depends on whether it's a 351 Windsor (small-block) or a 351 Cleveland (big-block), and also on the type of ignition system used. There's no single answer.

You MUST consult your owner's manual. This is the definitive source for the correct specification.

However, a common range for these engines is 0.035 to 0.045 inches. But again, don't rely on this! Check your owner's manual. If you don't have the manual, you can often find a digital version online through a Ford parts website or a classic car resource.