66 Spark Plugs

[Rich Freeman]

What is the suitable replacement for a 66 327/350 spark plug? I know the book calls for AC-44. Currently I have AC-45 with one wide green stripe in the car and it seems to run fine. Is this an older OEM plug? I've read some of the archives and saw where the Champion J??Y (I forgot the #)is the most comparible in the 45 heat range with good results. Any other suggestions?

[Dave S.]

Re: 66 Spark Plugs

If you have 3 equal and 1 unequal stripes on your AC plugs you have the earlier Made in USA plugs. In my opinion the pre 80's AC plugs are superior in quality to most others and are a very good choice for a Corvette. AC-44 or AC-45 should both perform well and last for many years. If they need a good abrasive cleaning you can do it without fear of destroying the plug. Most times the heat range selection is a matter of personal preference. I have found the heat range "3" (as in 43) may be to cold.

[John H.]

Re: 66 Spark Plugs

I used to have some fouling issues with 44's, and switched long ago to the AC R45S plugs; cured fouling in my '57 270, and they work great in my '67 327/300 and in my (stock) '69 Z/28 as well. 46's were great for around-town driving (and were used in production, in spite of what the Shop and Owner's Manuals say), but they were discontinued about two years ago.

[Rich Freeman]

Re: 66 Spark Plugs

Thanks for the replies, however, I wasn't very clear on my first post. The plugs I took out of my 66 only had one green stripe and said AC-45 (in green letters). What are these? If they are old or OEM, I'd like to keep them and install a compariable plug for pleasure driving since I'm changing plug wires at this time. Since the originals are hard to find. What other plug would suffice. The 45s seem to run good, I haven't experimented yet with other heat ranges, so I guess I should stick with what works.

[Joe L.]

Re: 66 Spark Plugs

Rich-----

My choice----Champion J-12Y (or J-12YC with copper electrode) or J-13Y (hotter).

[Dave S.]

Re: 66 Spark Plugs

Rich,

If they have one green stripe I can say I am not familiar w/ them. The pre 60 AC plugs have ribs w/o green stripes and then the 4 equal stripe AC plugs were introduced in the 60's. I'm not sure when the 3 equal and 1 unequal stripe plugs were introduced but my guess would be in the mid 70's.

[Jim T.]

Re: 66 Spark Plugs

I am with Joe on using Champions. I have used them in my 68 327/350 since about 1973.

[Tom Merkel]

Re: 66 Spark Plugs

John - What does the "S" in the plug you referred to mean? Extended tip, maybe?

I'm curious because I once tried an extended tip (AC-45SP or some such number), and it fouled repeatedly after only 100 mis. or so.

My stock AC-44's work perfectly, however, in my '67 L-79.

Tom

[Jeffrey S.]

Re: 66 Spark Plugs

Dave
The 3 thin and one wide stripe was introduced in approximately 1973. The 4 thin bands were introduced in 1960. The plain ones were used from 1956 to 1959 (and again in the 1990's made in Mexico although they had a thick boss at the top).
Just my 2 cents.
Jeff

[Jeffrey S.]

Re: 66 Spark Plugs

Tom
The "S" suffix is for "extended tip". The "SP' suffixes are for extended tip, platinum electrodes.
Jeff