I saw a long test somewhere on plugs, a real objective test ---and yes , Bob, Autolite won it , for “normal” conventional plugs, also NGK was right there . Champion came out at bottom. Why? Who knows, just the way it came out. They reduced volts, ran hard , dyno HP , etc etc Cannot remember details perfectly now. But if you went above the “normal” $ plug, dual ground electrode Bosch (platinum) came in as best plug. Interesting that more expensive Bosch ones with 4 grounds did not. Discussion was there, saying 4 grounds ?? shields initial lightoff, so ?? HP drops slightly . Bosch English descriptions confusing, one with 2 ground electrodes called 4 gap or something. Watch out. Got wrong ones first.
Why I was SO into that plug info , about 5 years back, I had an interesting experience, for what it is worth, on 97 JEEP 4.0 from new ; had factory HD long service special plugs , platinum I believe , supposed to change at ~ 30K(??) , I did not, they were firing fine . My own .02,= if they light the gas, no skip, they are working fine. Rest of it (the widely dispersed BS) gets filed alongside 2000 mile oil changes . I eventually drove that JEEP to 305k. And similar 02 4.0. I think 4.0 right up there with slant six. Maybe even better. Interesting fact, 4.0 AMC had more HP and torque than MOPAR truck 360 v8 in 80’s..
Although Chrysler managed to screw up AMG design with dirt cheap, thin wall pistons that crack the skirts at oil ring at 150k. About 2000 MY up.
But one day, JEEP with hi miles on plugs started to skip / run rough occasionally at 60-70 mph at about 105k after engine change . (ex ran it out of oil—that took 35 k miles) . So thought ,hmm NOW I do have to change the plugs. One day soon,-- as soon as rush is over. ! Within 1500 miles it basically suddenly stopped running, after limping for 5 miles, died at side of road. My “mental diagnosis” went immediately to coil (had died before --coils crack on 4.0 , before coil pack design, as rust on exposed E-I type coil core mounted near front of motor causes mechanical swelling, cracking the coil epoxy( bring back oil filled coils!) ) ; so changed coil again . No go..went though ignition etc all that stuff. Finally got into plugs, new Bosch dual ground plugs , it started right up, ran perfectly. So ALL the plugs failed essentially at once at about same miles. Really wild thing that is!!!. When pulled, ground electrode was almost gone, very wide gap, sharp point left (sharp was/should be good!) . Lots of knowledge-- in my opinion-- in this. Gap opens, by itself , by burning ground, you should check it, reset it, certainly ~ 30k or so. –gap too big, =no jump. . Dual grounds on plugs are probably very good things , ought to help this 2X? . Platinum or Rhodium sharp small center electrode that does not burn is a very good thing. I bet if I had bent what was left inward it would have run another 50k . Not advocating any of this, but really good info . After all, from engineering view, a plug only has to carry electricity in , to the gap; if ceramic insulator is clean and not shorted, (says engine is ok, rings etc—no carbon ) what else goes wrong? Deposits? Maybe in 1960. Lead. But clean gas , clean running, and high power spark from electronic ignition, now the ground side apparently burns off first, and it cannot jump the larger gap..or it jumped somewhere else outside the plug due to higher volts needed outside to jump inside gap (tower to LV 12v nuts not uncommon on MOPAR , almost says loudly to you: burned ground electrode , or open wire ---if you see that jump at night—resulting skip drove me crazy on B block 383 Charger and 440 challenger back in the day, when ~ new—mainly in rain by the way—one wet night opened hood in dark and saw it jumping to nuts at coil tower !!) Silicone grease fixes that, and cleaning tower.
Lately revisited this plug story for slant six with a slight one cyl skip, about 25 -30 k since rebuild. Went to slant six guys site, they swear by certain NGK. So spread the love. Put NGK in it. But for high performance and longevity, would still go Bosch with two ground electrodes.
Aside from above, all regular plugs of correct heat range will work. New. Differences really should be non existent?
And Autolite or NGK may be best of those, over the long term
New is apparently less than 30k on them.
I run Autolite 85 plugs in my G, and it runs fantastic, even with fuel containing ethanol. Follow the tune-up procedure in the factory service manual.
What is the latest recommendation on spark plug type/brand for 61G?
Posted by: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>
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