...and possibly punch holes in the pistons or break off an electrode, can this be right? The "original" used plugs in the photo are NGK BP5ES-A (yes, I was running quite rich), the comparable-sized plugs are Autolite 66, and the longer plugs are NGK ZFR5N 3459 (I've seen recommended here). I can always hand-crank to ensure that they don't collide, but perhaps someone has already put this concern to rest?

My slant six is a 225 in a 72 Dart and should be all stock (but built in Mexico). I've also read that I should remove the metal crush rings, but that would make it an MM or two longer in that chamber.

I tried to insert the photos here, but failed despite follwing the instructions on site. Links were my next best option.
Thanks for any insight gurus!
-Drew

https://drive.google.com/file/d/0B51AzY ... sp=sharing
https://drive.google.com/file/d/0B51AzY ... sp=sharing

Use ZFR5N (3459) without metal crush washers. They will not hit the pistons or anything else.

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Too many people who were born on third base actually believe they've hit a triple.

Alright - you have my trust on this and my thanks for a comprehensive HEI explanation! I'll give this a go next weekend when I get to work on adjusting the carb.
Thank you,
Drew

Unless this is a 12:1 compression ratio motor where you took a generous cut off the head and deck... the piston on a stock 225 sits below the deck about +/- 3/16".... even the extended electrode is still above the deck in the chamber on the stock head by a similar amount...


At one time I took a head and bought an example of different spark plugs with longer threads and reach just to see where they would sit in a stock chamber... the one for a modern Corvette was the only one that would be impeding the top of the piston if installed... (Note to all, don't use a longer threaded plug as the carbon build up will prevent it from being uninstalled... also moving the kernel can act like altering your timing so you may have other issues...FYI)