Packard Forum Index » General

They came out with coated plug technology for the HEI systems. You're probably around 30-35K VDC volts coil, where HEI run around 50K VDC. The old plugs didn't take the higher energy spark very well/didn't last. The coating protects it from spalling, melting, etc
Unless you're going to change the ignition system, electronic/hotter coil, the coated plugs won't do anything.
If you want a hotter plug then Autolite or competitors may offer in the same series. Usually the last number goes up one.
We used to laugh about those JCWhitney spark plug claims. Glad we got a bona fide testimonial over 4 decades no less! My buddy in HS, put them in his '59 Chevy 283. Of course gas was ~$.34/gal or less, so who worried about gas mileage? We could cruise all night on our pocket change, less beer money.
I'm trying to recall what they were called, "fire injector?" similar to the E3 technology of today. I think JC is back in busy-ness owned by some other company.
Lower compression means easier to ignite, so I'd look at my fuel/air ratio, if It's sooting or having serious deposits. Any fuel additives I'd cease using. Some of the octane booster additives of today use alkali metal salts. Others dose MMO, which is a venial sin according to the EPA.

Keep in mind spark plug reach (length of threaded section), electrode design (projected or not), heat range (hot to cold) and electrode and core materials. All of these can be mixed and matched for different applications.

Then there are resistor and non-resistor types. In addition reach thread types (10mm, 14mm, 18mm), and flat seats with gaskets or not and tapered seat.

Lots of things to consider.