Machines are collection of parts. They all combine together to give you desired performance. Stable voltage is one core part of smooth engine running. Coming to your point, carefully check if there is a volt drop at any point. Volt test is not that which our street mechanics do, use multimeter and check volt on battery, both when car is switched off and check it after starting engine, check gravity of each cell of the battery, note difference between gravity of cells, if liquid battery, with hydrometer. Diagnose if there is any sign of volt drop. Check your ignition coil, distributor (if there is), plug wires carefully. If there is any sign of volt drop or surge, then correct the problem. Definitely every car needs powerful spark in the plugs. Pls don't go for such mods without diagnosing cause of the problem. If volt is fine, you may have further options to upgrade Ignition i.e. coil, coil cable, distributor and plug wires. MSD Ignition has wide range of performance products. Oh one more thing with volt, get good grounding wires, this could be good mod for stable current.