The spark advance on a 5.7 Vortec engine depends on fuel quality, engine modifications, and driving conditions. Generally, the spark advance for a stock 5.7 Vortec engine ranges from 10 to 15 degrees before top dead center (BTDC) at idle. However, it can vary for different applications. Refer to the manufacturer's specifications or a reliable source for your specific vehicle to determine the optimal spark advance settings.