so what NGK's are prefered?

7100, 6987, 6441, 3271????

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2003 Liberty Freedom Edition
1988 Suzuki Samurai

None. the NGKs spec-ed for the KJ suck, They won't make it 30,000 miles! I am a big fan of NGKs, but facts are facts. Most people prefer the Autolites, They are much better than the NGKs.

I'm stubborn though, so I'm experimenting with the NGK Iridium plugs, I will check them in a few days to get a progress report.

Those NGK's work the best for power and economy handsdown, you just have to replace them every 25K

I'd go as low as 20K. The only economy difference with the Autolites was an improvement, because after 30K the copper electrode was barely long enough to protrude from the ceramic insulator (not an exaggeration). If you can quantify that statement with some actual evidence, I'll gladly eat my hat.

That level of quality from a modern plug is just unacceptable.