In spark contrast: The difference between plugs for classic and modern cars


Let’s talk about spark.

In modern, computer-controlled cars, ignition is reliable to the point where you rarely consider that it might fail. You have coil-on plugs, also called stick coils, snapped onto the tops of spark plugs, with not even a plug wire between them. The stick coils and plugs are typically hidden inside the engine under a plastic cover that looks like the top of a Shop-Vac. There’s no distributor, because the functions of advancing the spark with increasing engine rpm and distributing it to each cylinder are performed electronically, with everything controlled by the car’s electronic control unit, or ECU. Something like a bad crankshaft position sensor might prevent the ignition system from being triggered, but it’s rare for the entire ignition system to go bad.

This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2018/06/25/the-difference-between-plugs-for-classic-and-modern-cars


Are platinum plugs okay if you upgrade to electronic ignition with a higher-powered coil?


My opinion is that newer, fuel injected vehicles control fuel mixture better, resulting in the plugs not getting boogered up with carbon deposits, so it makes sense to use a longer lasting (platinum) plug. If you can tune your old car to run around stoich (not to rich not too lean) to burn off the carbon, then the platinum plugs can be installed and run for 100K miles too. Platinum plugs just don’t wear the electrodes like conventional plugs. The question becomes who runs their old car 100K miles anymore? Conventional plugs will last about 30K miles in a properly tuned car, regardless of whether the car is new or old and platinum’s last around 100K, as long as your diligent with tuning, and especially if you only drive the car on nice days in the summer. Throw dead of winter cold starts in there and all bets are off!


I’m really glad this subject came up because I haven’t had a chance or reason to relay this to anyone else except my wife and she could care less.
Now, the car I am speaking of here isn’t one most of you would care to own but we do anyway. We bought a 2006 Kia Spectra EX brand new and we still have it. I am very meticulous with maintenance and care and cleanliness of each vehicle I have ever owned since 1969. And the Kia is no exception. It had platinum plugs in it from the factory and I decided to give them the 100k-mile test. I mean why not? We rarely drive it on trips and I knew the car would let us know if they were not capable of firing properly. At 100k miles, I took the car to the Kia store where we bought it new and told them to change the spark plugs. I wanted the exact same kind of plugs it had since new and I wanted my old plugs back.
And guess what! Those old plugs still looked great! So, now I know for a fact that platinum plugs really will last for 100k miles on a computer-controlled car running strictly on regular unleaded gas. Good to know!


I believe that the original article on plugs was incorrect about the voltage required on spark plugs. I worked with a major spark plug company for over 35 years. On a standard copper tipped spark plug the voltage required is slightly higher than on platinum tipped spark plug. As a matter of fact, Iridium tipped spark plugs require even less voltage than even the platinum plugs. The reason is the size of the center electrode. There is less surface are to have to ionize, hence a stronger more focused spark. Precious metals on the tips of spark plugs don’t wear away like the older style plugs - so they last longer. That’s why you see platinum plugs lasting 100,000 miles and Iridium plugs lasting over 150,000 miles. In a classic car you could use any type of plug you want, but remember that most collectable cars get better maintenance than your regular everyday ride - so if that is the case, go with the cheaper plugs. Myself, if I take a plug out - I usually replace it with Iridium if it is available. That way, if I never change the plugs again I know that’s they’re still OK. . . unless you have a problem with the ignition system or the carburation – because that would foul the plugs anyway.


I agree and have been putting platnum plugs in my vintage vehicles and enjoying improved performance. Most extreme example is my ‘52 Harley Panhead with a sidecar, points and 6 volts. After sitting for several months I can offer two priming kicks and then start it on the first kick after turning the ignition on. Did I mention this is a kickstart only and 6V ignition system?