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Spark plug expertise needed........


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Our 1937 Packard Super-Eight shop manual stipulates AC 103S or Champion Y-4 plugs, which are 10mm.  At some point of time the head was rebored to accept larger plugs.  When we acquired the car, it had AC Delco 45S plugs.  The 45S places the spark deeper in the combustion chamber.  Is there any scientific reason to place the spark in any particular area of the chamber?

 

 

 

Second question.....

If an engine specifies a non-resistor plug, does using a resistor plug cause a positive/negative/neutral effect?

 

Thanks for checking out this post.

 

 

 

 

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A 1937 Packard did of course take the old 10 mm plugs -- but if it had been changed to use 14 mm spark plugs -- then, you have no choice, you must use them now and forevermore...

Non resistor plugs have not been manufactured in many years -- so unless you are fortunate to find some N.O.S. 45S AC spark plugs -- and you are going to pay bigger money for them --

   You are going to use the R45S (R for resistor) A C spark plugs.

      Non - resistor spark plugs have no resistors, total performance. With resistor plugs, you lose a little bit of performance, but truthfully, not enough to "worry about".

   If you have any questions or comments, feel free to call me -- Craig --

         516 - 485 - 1935 .... New York....

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Yes, spark plug location, either by the actual physical location in which the plug enters the combustion chamber or the depth at which it protrudes into the chamber affects flame propagation. Race car mechanics even take it to an extreme and will "index" the spark plug electrode grounding lugs so they point toward the center of the combustion chambers and (or so the theory behind it goes...) don't interfere with the flame as it travels across the chamber to push down the piston.

 

Resistor plugs cut down on radio static, mostly on the longer wavelength (AM) spectrum

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Looking at your photo I'm sort of amazed that whoever did the conversion didn't aim to get the threaded portion of the plugs to sit at the same depth of the originals, I'm guessing that the 45s is at least 1/8" or more longer than the 10mm plug; wondering how far above the piston the electrode sits ?

 

As to the plugs themselves, the 45s is going to run much colder having almost twice the ceramic insulation of the original, but I'm assuming, it's  been running ok with them for some time, would be interesting if you could find some plugs of similar size to the originals in 14 mm (i.e. electrode depth and insulation)  and see if they made a difference in performance. 

 

Re plug location,  as Dusty explained their positioning in the combustion area is critical for design performance, engine designers go to a lot of trouble in positioning valves, plugs etc to achieve the best performances.

 

Although it's probably not worth it now, a better solution to going upsize with the plugs would have been a screw in adaptor to accommodate the 10 mm plugs in the 14 mm hole. 

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The S on the AC plug is an extended tip. The 5 is the heat range. If you think the 45s are too hot you could try a plug like AC R44 which would be 1+ heat range colder. ACDelco does not make many of the heat range selections they use to so you would have to find them nos.

 

Dave

 

 

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24 minutes ago, gossp said:

Be warned, if you use lawnmower plugs and leave your hood up at a show, a shocking number of people will notice. 

 

Well then you could use Autolite 295. It is a full size plug, non-projected tip, non-resistor, heat range equivalent to AC-45. Technically it is a lawnmower plug too, but it doesn't look like one. IMHO it looks decidedly modern next to an LM-46.

 

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Edited by Bloo (see edit history)
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12 minutes ago, edinmass said:

While on the subject of plugs.......is anyone making them with the black parkerized finish anymore? 

 

IMHO you are lucky to get non-resistor plugs at all, and the LM-46 is all by itself for black finish.

 

I believe a few AC and a few Autolite types are still black. Not many.

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Green Spark Plugs in the UK has AC 45S plugs for 2.50 British pounds each.  For people in the US you pay the Excl Tax rate, so it works out to $3.25 at the current exchange rate of $1.30 per British pound..

 

I have purchased several item from them recently for my Triumph TR4 and the shipping was quite reasonable.

 

https://www.gsparkplug.com/1x-ac-spark-plug-45s.html?___SID=U

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Last time I looked the Autolite Mexican production moved to China for their brand and ACDelco older applications. The plugs don't look the same as the Mexican or US manufactured plugs.

 

Not sure who is making the UK plugs.

 

Dave

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