NGK XR4 Spark Plug

[Joe C.]

Looks like just what I was looking for. I'm going to buy a set to replace the AC44's.

[Randy S.]

Re: NGK XR4 Spark Plug

Looks like just what I was looking for. I'm going to buy a set to replace the AC44's.

Joe,

Maybe I missed a prior thread but why are these going to be better than than AC 44 ( or 45S in my case)

Randy

[Joe C.]

Re: NGK XR4 Spark Plug

Joe,

Maybe I missed a prior thread but why are these going to be better than than AC 44 ( or 45S in my case)

Randy

Many here prefer the AC 45 plug to the AC 44 for around town driving. Further, many here prefer the NGK, Nippon Denso, or Champion plug to the AC brand. Further, some say that in many cases, and especially if properly indexed (if piston crown to spark plug clearance requires it), an extended tip plug will work for a vintage SBC, and with it, the benefits of better location and improved fouling resistance.

The NGK XR4 spark plug combines all three of these desirable characteristics, as well as the fact that it is a "V-Power" design, which has a "V" profile cut into the ground electrode. This supposedly contributes to easier firing, requiring lower voltages. If this is true, then it would help prevent misfiring under higher engine loads where maximum voltage is required in order for a spark to jump the gap. In any event, I don't see how it could hurt. This spark plug corresponds to an AC heat range of "5". It also has an internal resistor for noise suppression.

[Stuart F.]

Re: NGK XR4 Spark Plug

Joe;

Thanks for the "heads up". It's good to know we have more options in this regard. As for me, having electronic ignition conversion, I don't change near as often as in the old days so I want a plug that will work consistantly over time and not rust into my old 461-x heads. I use Champs now, but sometimes you can't always find what you want easily. But then I have about 6 new sets waiting on the shelf in case I live that long, Ha!

Stu Fox

[Gene M.]

Re: NGK XR4 Spark Plug

Many here prefer the AC 45 plug to the AC 44 for around town driving. Further, many here prefer the NGK, Nippon Denso, or Champion plug to the AC brand. Further, some say that in many cases, and especially if properly indexed (if piston crown to spark plug clearance requires it), an extended tip plug will work for a vintage SBC, and with it, the benefits of better location and improved fouling resistance.

The NGK XR4 spark plug combines all three of these desirable characteristics, as well as the fact that it is a "V-Power" design, which has a "V" profile cut into the ground electrode. This supposedly contributes to easier firing, requiring lower voltages. If this is true, then it would help prevent misfiring under higher engine loads where maximum voltage is required in order for a spark to jump the gap. In any event, I don't see how it could hurt. This spark plug corresponds to an AC heat range of "5". It also has an internal resistor for noise suppression.

Joe,
Are these plugs much longer than AC44's?
Do they require indexing with L79 pistons for clearance?
What is heat range "5" compared to AC44's?
What is hex size?
Lastly and most important are they USA made?

thanks I enjoy your posts

[Joe C.]

Re: NGK XR4 Spark Plug

Joe,
Are these plugs much longer than AC44's?
Do they require indexing with L79 pistons for clearance?
What is heat range "5" compared to AC44's?
What is hex size?
Lastly and most important are they USA made?

thanks I enjoy your posts

Here is one of the many places you can find these, along with a description:

http://cgi.ebay.com/ebaymotors/NGK-5858-Spark-Plug-XR4-1-Plug-New-_W0QQcmdZViewItemQQhashZitem4aa439998bQQitemZ320582818187QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

I had my local NAPA store order in a set for me. They are gasketed, not tapered. The reach is the same as any other extended reach plug, and many report having no interference problems when fitting to unmodified engines. Indexing may not be required, but I recommend it very highly in this case.............not only for clearance, but for consistent burn times. Stock quench can vary from a low of (about) .046" to as much as .056" or MORE. My engine's quench is ultra low, @ .033" plus/minus .001", so I'm hoping there won't be an interference problem. I'll report back if there is.

Many, but not all NGK plugs are made in USA. I do not know where these particular plugs are made. They are 13/16" hex.

More:

http://ngk.com/more_info.asp?AAIA=1323470&pid=3314

CORRECTION TO POST #3: The center (positive) electrode is "V" cut, not the ground electrode.