Affect of Cam Timing on Fuel and Ignition maps

For a vehicle with variable valve timing, I can see how an experienced tuner may work on fuel, ignition and also cam timing at the same time on the dyno, to get the most out of the engine quickly. However, for a novice tuner, who would probably go at it like, fuel first, then ignition, and finally cam timing, is there a dramatic affect on the fuel and igniton maps when optimising the cam timing?

Take an FA20 for example where you are working off a base map rather than starting from scratch. Using OEM cam timing, you tune your fuel and ignition maps, then following this you might start working on the cam timing. Is it relatively safe to do this, or is there a high chance of running into knock conditions when adjusting the cam timing?

Hey Nick,

In speed density, tuning cam timing is an iterative process as the changing the cam angles will change the engine efficiency and affect the fuel quantity needed to achieve your target. The way I usually do it is tune fuel and ignition timing for a given cam angle, then change the angle and check the effect on the fuel trims and torque values. If the trims are positive (ECU is adding fuel), the torque should increase as well as the engine is becoming more efficient, therefore you'll need to add fuel to your map in that area. If the trims are negative (ECU removing fuel) the torque should decrease and you are moving away from the optimal cam angle.

If you have access to a load bearing dyno and have a standalone ECU, doing this in real time in steady state will help get a "shape" to the VVT map that will help you when doing your ramp runs. Rule of thumb is that the cams position will be advanced in the lower RPM region and retard with increasing RPM.

Remember that piston to valves clearance can be an issue while tuning cam timing, especially if the engine had modification like decking or different internals. Finally, I think there are a couple of webinars in the archive if you wan't more information.

I'll just add that fuel target may not need to change as you vary cam target in small increments, but as Frank mentioned the engine VE values needed to hit that fuel target may change, or on a MAF based tune the MAF scaling may need altered to stay on target.

Altering VVT can alter cylinder filling and pressure, so ignition timing adjustment is often required. Backing timing off a few degrees can avoid knock while trying various cam angles to figure out where you get best cylinder filling and torque.