* Specific Z303 Camshaft Manufacturer: Several companies reproduced or offered similar cams under the "Z303" designation. Each might have slight variations in lobe centers and lift.
* Engine Modifications: Head work (porting, milling), intake manifold, exhaust system, compression ratio, and other modifications all impact ideal timing.
* Fuel Type and Air/Fuel Ratio: The fuel you're running and how well the engine is tuned will influence the optimal ignition advance.
* Desired Performance Characteristics: Are you prioritizing low-end torque, high-RPM power, or a balance? This influences the timing curve.
Instead of seeking specific numbers, here's how you should approach finding the optimal timing for *your* specific setup:
1. Consult the Cam Manufacturer's Instructions (if possible): If you know the specific manufacturer of your Z303 cam (e.g., Comp Cams, Crane Cams), their instructions might provide a recommended starting point for initial timing. This is your best bet.
2. Start with a Baseline: A common starting point for a modified 5.0L with a performance cam is around 10-14 degrees initial advance at the distributor. This is just a rough estimate and should be verified and adjusted.
3. Use a Timing Light: This is essential for accurately setting and checking the ignition timing.
4. Gradually Adjust and Test: Increase the timing in small increments (2 degrees at a time), then test drive the vehicle. Listen for pinging (detonation) under load. Pinging indicates that you've advanced the timing too far for the fuel and engine conditions. If you hear pinging, reduce the timing. You're looking for the point where you have maximum performance without detonation.
5. Consider a Tuning Tool: For precise tuning, an aftermarket ignition timing controller or a dyno session with an experienced tuner can provide significantly better results than trial and error. This allows for a dynamic timing curve adjustment throughout the RPM range, far more accurate than simply adjusting the initial timing.
In short: There's no magic number for timing. Start with a baseline, use a timing light, listen to your engine, and proceed incrementally. If you're serious about performance, professional tuning is highly recommended.
