Engine Performance refers to… you guessed it… how your engine performs. Tune-ups are designed to check your engine to see if it’s performing at optimal settings for power and efficiency as recommended by the manufacturer. Although many tasks on newer cars are automated by your car’s computer, tune-ups ensure that things like idle speed, fuel-air mixture, spark plugs and the carburetor are properly calibrated and working at maximum capacity.
The first thing that comes to mind that would help everything performance-wise is weight reduction. Less force acting on the engine, less weight acting on the suspension, less inertia to overcome.
Ways to improve overall horsepower? And you’re asking for most effective? Forge the internals, port the head, spend 20,000 on the engine and then run 50–60PSI on a giant turbocharger.
Improving handling? A coilover kit is the fastest and most cost effective way to do it for most people. Plus… Okay, I’ll be honest here. Most of the time, “most effective” means “what can I do that’s cheap but I won’t waste my money on?”