Hello everyone! I'm back again after another multi-year disappearance!

This time I have a fairly introductory question but one that has been causing me some headache: Which spark plugs should I run for my engine?

I have used the search function here to the best of my ability and I even checked out the FAQ.

So here is the deal, I have a 225 Slant 6 in a 1964 Dodge Dart GT. I have a super six intake, Weber 2-barrel (currently a 32/36, but will likely be changed to a 38/38) and a later 2.25" outlet exhaust manifold.

I'm trying to give my engine a bit of a tune-up and the plugs right now are very black. I suspect the car has been running rich while I have been trying to tune the carburetor.

I have been recommended to buy the Autolite AP66 plug by Performance Distributor (I'm considering buying one of their new Tri-Power distributors for the slant 6). However, I also read an article over at AllPar.com about slant 6 spark plugs (https://www.allpar.com/fix/spark-plug-tubes.html) and there is a blurb there where a guy named Dan Stern recommends the either the Autolite 925 (now discontinued, but replaced with the Autolite 985) or he recommends the NGK ZFR5N.

Both the Autolite 985 and the NGK ZFR5N have extended projection tips. The rationale behind using these in the slant is explained in the article.

I would like to know what other people with this vintage of engine run and under what conditions?

Thank you for your time!

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1964 Dart GT
225 "Super Six" w/ Weber 38 DGES
GM HEI, Nippon Denso 80A Alternator and high torque mini starter

I have used both the Autolite 985 and NGK ZFR5N in drool tube heads...once in a stock 1967 225, and a 9.6:1 daily driver motor-super six and Holley 2 barrel.

The NGK is of better quality, the extended electrode worked well for the stock motor, and was OK, but I think not as necessary in the
mid-performance motor. AP66 looks to be the standard stock style of plug.

The stock motor ran points then stock mopar EI conversion, the ZF mid-perf engine ran the same EI conversion.

I would not plug that much money for the Tri-Power Distributor, the module is not located in a good place... and you can still get an HEI module, wires, and stock EI
distributor and recurve spring for about 1/2 that price and an afternoon of elbow grease... (and if they really were going to recurve it properly,
they would also ask for your transmission, rear ratio, and tire size to properly check your cruise rpm vs. engine power band... sadly I could have
done the recurve for you for much less and you would have gotten the distributor curve map and initial setting recommendation, but my Sun Machine is toast...)

"Tri-Power": Not advisable. Overpriced Chinese junk with thoughtless (ignorant/wrong) module placement. Better and cheaper: HEI upgrade

Spark plugs: Autolite is now Chinese junk, too; get the NGKs. Read up on this and all the rest of the tune-up parts and technique suggestions in this post.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thank you both for the responses.

At this time I haven't dropped any money on an upgraded ignition system. The previous owner did do the Chrysler orange box conversion to eliminate the points and that has been working, I'd just like something better/hotter.

I certainly have no problem with doing a more "homebrew" conversion using a GM HEI module, so I'm going to read up on that. I love the ingenuity of the slant 6 community!

I have no problems with NGK as a brand, good quality Japanese parts. I will look into getting a set of ZFR5N plugs.

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1964 Dart GT
225 "Super Six" w/ Weber 38 DGES
GM HEI, Nippon Denso 80A Alternator and high torque mini starter

Another vote for the NGK plugs. I ran Bosch in both my turbo and non-turbo engines; the non-turbo ran well enough but no better than with Champions it had before. On the turbo engine the center electrode melted away rapidly. I suspect Bosch and others have shipped the job overseas, where quality takes a back seat to making a buck.

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If it was easy, everybody would be doing it.