'66 Sparkplugs (Again!)

[Edward S.]

Before posting this, I checked the archives and read several discussions relating to the sparkplugs that replace the AC 44 plugs used in many applications including the '66 327/300. I followed Duke's suggestion to replace the AC 44 with the slightly hotter, transistor-less NGK B4 or Denso W14-U. When I checked with the local parts store, they indicated they did not show the NGK B4 as correct for my application but showed it as an outboard motor application and they did not carry the Denso plug at all. I thought I should post this before moving forward in the event some new information is available.

Thanks in advance.

Ed S

[Larry M.]

Re: '66 Sparkplugs (Again!)

No new information. They should be fine.

Also AC 45 (old stock, available on E-bay or from some of the Driveline ads), or AC R45S (currently available, resistor with extended tip) will also serve you well. The 44's are generally too cold for normal street driving......certainly the way we now drive these old cars. The 45 or R45S are a better choice if you want to install AC/DELCO.

Larry

[Duke W.]

Re: '66 Sparkplugs (Again!)

I believe you can find the Denso and NGK spark plug catalogs online or the parts store should have a paper copy.

Look at the cross reference charts for AC 45 and they will say W14-U and B4, respectively. Further catalog research will show that they are 14 mm, 3/8" reach, 15/16" hex, conventional electode (non-extended tip), gasketed, non-resistor plugs. Maybe some outboard motors use them too, but this common plug geometry is also correct for all early small blocks until they went to resistor types, and then the taper seat, gasketless design.

My ten-year old Denso and NGK catalogs car application charts don't go back further than 1972.

Many small block owners have used these plugs successfully. My preference is the Denso, because of the "U-groove" ground electrode that provides more sharp angles for spark propagation.

I wish I had a nickel for every response I've had to post when the kid behind the parts counter didn't agree with my recommendation.

Duke

[Edward S.]

Re: '66 Sparkplugs (Again!)

Thanks, guys. I really appreciate the input.

[Wayne M.]

Re: '66 Sparkplugs (Again!)

...... My preference is the Denso, because of the "U-groove" ground electrode that provides more sharp angles for spark propagation.....

Interesting, Duke -- I "inherited" 43 NipponDenso W16FS-U plugs (4 boxes of 10 plus 3 individuals), in a big box of over 100 other electrical parts which I won eBay 7 years ago, just to get an NOS 1st design TI volt reg 1116368.

Checked the Denso-to-AC Delco X-reference chart online, and see that the W16FS-U equals the AC 44F. So my question is what does the "F" mean on the AC plug ? Would the Densos be OK for my '65 L76 with (I think, 11-to-1's).

I see what you mean by the "U-groove" (see pics below).

[Duke W.]

Re: '66 Sparkplugs (Again!)

AC suffix "F" = 1/2" reach. Small Block plugs are 3/8" reach, so...

The additional 1/8" reach appears to be unthreaded and could interfere with domed pistons. They might be okay with flattop pistons, but I'd be leary of using them unless you could do a trial fit with the head not bolted to the block and use some modeling clay to check for interference.

The spark would be moved closer to the center of the chamber, which is good and reduce chamber volume by a cc or so for more compression.

If anyone wants to experiment with a non-domed piston Gen I Small Block, you might have some takers.

Duke

[Joe C.]

Re: '66 Sparkplugs (Again!)

I believe you can find the Denso and NGK spark plug catalogs online or the parts store should have a paper copy.

Look at the cross reference charts for AC 45 and they will say W14-U and B4, respectively. Further catalog research will show that they are 14 mm, 3/8" reach, 15/16" hex, conventional electode (non-extended tip), gasketed, non-resistor plugs. Maybe some outboard motors use them too, but this common plug geometry is also correct for all early small blocks until they went to resistor types, and then the taper seat, gasketless design.

My ten-year old Denso and NGK catalogs car application charts don't go back further than 1972.

Many small block owners have used these plugs successfully. My preference is the Denso, because of the "U-groove" ground electrode that provides more sharp angles for spark propagation.

I wish I had a nickel for every response I've had to post when the kid behind the parts counter didn't agree with my recommendation.

Duke

If you find the "U-Groove" concept appealing, then the NGK brand markets a line incorporating it, called "V-Power". The positive (center) electrode is ground with a "V" cut which is intended to provide added fouling resistance, a purpose exactly the same as the Denso's "U-Groove".

I have found that the NGK XR4 is a good match for Gen I smallblock Chevys:

It is 14mm, 3/8" reach, gasketed, V-Power, heat range= AC 45, 15/16" hex, extended tip, non resistor.

[Duke W.]

Re: '66 Sparkplugs (Again!)

The "R" in XR4 means it's a resistor plug.

[John D.]

Re: '66 Sparkplugs (Again!)

FWIW I've had AC R45S's in my 67 L79 for along time with no issues whatsoever

[Timothy B.]

Re: '66 Sparkplugs (Again!)

John,

To add to your post whenever you do a tune up just lightly glass bead the plugs and regap. If everything is adjusted properly motor will run like new. You can save the money to buy two gallons of gas..

[Stuart F.]

Re: '66 Sparkplugs (Again!)

Should someone, like myself, who has run AC-44's (or Champion Equivalents) for nearly 50 years with a 63 L-76, is there any good reason to go up in heat range? My only experience going up one heat range was with a 58 fuelie engine and it did not like them very well. Sure, if I still had points I might have good cause, but I don't. Any plug concerns I had back in the day I've left behind since converting.

Stu

[Timothy B.]

Re: '66 Sparkplugs (Again!)

Stu,

Pull a few out and look at them, if they are burning clean leave them, the only reason to go up in heat range is to prevent fouling because of soot build up. The additional heat keeps the plugs cleaner, the way you drive there may night be a problem.

[Dennis O.]

Re: '66 Sparkplugs (Again!)

I went through this about a year ago and ended up using the Denso's. A little judicious use of our favorite austion site and I ended up paying $.50 apiece for 4 boxes of 10 plugs; $20.00 plus 8.00 shipping. I have a '67 L79 and a base motor '68, so that's OK. Sometimes obsolete parts aren't.