What is the initial ignition timing on a 1979 351-400M?

The initial ignition timing on a 1979 351M-400 (Ford's 351 Modified, often mistakenly called a 400 due to its displacement being close) is not a single, universally set value. It varies depending on several factors including the specific vehicle application (truck, car, etc.), the carburetor used, and even the emission control system installed.

You cannot rely on a general number found online. The only reliable way to determine the correct initial timing is to:

1. Consult the owner's manual for your specific 1979 vehicle. This is the most accurate source. The manual will specify the timing either in degrees BTDC (Before Top Dead Center) or at a specific RPM.

2. Look for a timing sticker under the hood. Many vehicles had a sticker indicating the correct timing setting.

3. Use a timing light. This is the most reliable method if you don't have the documentation. You'll need to connect a timing light to the engine and use the marks on the harmonic balancer to determine the current setting. Then, you'll need to adjust the distributor until the correct timing is achieved. This requires a degree of mechanical knowledge, and it's crucial to follow instructions carefully to prevent engine damage.

Attempting to set the timing without proper information could cause serious engine damage. If you're unsure, consult a qualified mechanic.