Speedtoys

https://www.hagerty.com/articles-vid..._3_HagertyNews

The Forgotten On

I use what I consider middle ground plugs. The correct temp Bosch plugs, but with silver electrodes.

Being one of the most conductive metals around doesn't hurt along with being harder than copper.

Petza914

I too like the silver electrodes for the older cars. Also, if you can find a 4 prong version with copper or silver electrode (Beru Ultra-X, Bosch +4, etc) in the correct heat range that cross-references to your car, I've also had very good luck with them, specifically in my carubrated 914. They don't usually result in a larger spark as electricity follows the path of least resistance, but on a conventional spark plug, once the ground electrode gets fouled or worn away where the gap becomes too large for proper conductivity, the plug is essentially shot. On these multi ground electrode plugs, the plug will continue to work much longer since it just starts using the next ground electrode and still makes a decent spark.

hacker-pschorr

Silver being harder has zero benefit in a spark plug. Fact is, there is zero evidence silver plugs offer any benefit outside of longevity and while copper plugs have proven to work perfect in some very high horsepower 928's, they are more than good enough in a stock one.

In your supercharged 928 I would highly recommend at minimum a WR7DC Bosh (or NGK equivalent) or better yet another range cooler - WR6DC. I've had zero issues with WR6DC plugs in my stock 80.

Single electrode so you can be certain of the plug gap. In a supercharged car like yours, these small things can be critical.

Multi-electrode plugs last longer, that's the only benefit. With my supercharged 81 I check the plugs in spring and sometime towards the end of the season anyway.

Speedtoys

"They don't usually result in a larger spark as electricity follows the path of least resistance"

But thats _100% exactly what you want_

If gap keeps you up, thats called maintenance, and you can check it as often as you like...or...follow the instructions. A worn wider gap is not really that bad, if it still sparks. A too narrow best-effort gap on +4 plugs...does have negative side effects.

ptuomov

From the comments to that linked article:

" 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. "