VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 AC44 Spark Plugs

Does anyone know a source for obtaining AC44 Spark Plugs...

Wes Marquis

You can try checking eBay from time to time.

have you tried NAPA?

I was able to find plugs at my local Bumper to Bumper but I had to order a box of them.

The AC #45 would be the correct heat range for a 1940 unless you drive at very high speeds every day.

Somebody please confirm, the AC-45 would be called a "hotter" plug than the AC-44????

With the AC spark plug numbering system (and most other makes) the higher the number the hotter the plug.
The AC43 was the cold heavy duty plug. For heavy duty truck use and high speed driving in cars.
The 44 was one step up and used in the later 235 engines and V-8's (higher compression engines)
The 45 was used in the the 1933 and up (originally the older models had a different number) (1941-48 had the little 10MM plugs).
There was a "mixed" plug used by Chevrolet, the 46-5 and 44-5. Used from 1949-1955 and have been discontinued for years.
The 46 was a hotter plug and was best for all city driving.
Then there was a 47 and 48 really hot plugs. They were for cars that burnt oil.
The 48 was also standard in some Buick straight 8 engines. The location of the plug in the cylinder head probably was the reason for its use.

No one engine can use just one plug (except for modern cars)....the heat range is selected by the type of driving and condition of engine. Observing the looks and condition of the old spark plug is the best indication of determing the correct heat range.
I use the AC45 in all my engines including the 283. They last forever.
Back when there was lead in the gas the plugs could lead foul in a few thousand milels or less. At one time cleaning was recommended every 3000 to 5000 miles to remove the lead deposits.
I know of some "modern" cars that have gone over 200,000 miles and the plugs were never removed.

Chevgene,

Is that an AC45R that you use?

Thanks everyone....

Wes

Originally I used the 45. When I ran out I went to the R45 resistor plug and had no trouble with them. Even had them in my 1934 and 1939.
Often is had been stated that the resistor plugs do not perform well in the older cars. I must disagree with that.

I run AC43 or 45 plugs in my 1938 HB Master. Bought both types at either NAPA and Advance Auto Parts a few years ago.I also have a set of C46 plugs I bought from a VCCA member, and was told they would work fine. Call some of the vendors in the VCCA that show NOS parts they can probably help.

Gene,

Thanks for the detailed info on AC (and most other brands) plug range numbers. Essentially the higher the number, the "hotter" the plug.

Thnx again....

Bill.

And now the rest of the story - if anyone cares.
AC also has a plug that has the number end with an S...like 45S.
This plug has an extended tip (insulator and eletrode) that sticks out farther into the combustion chamber. This plug was designed to burn off the lead deposits better. This AC version came out in about 1958, well after Champion and Autolight (or lite)
Autolite was the first to have the extended tip spark plug. They were introduced in 1955 or 1956 (going by memory) and were called "power tip". I used them in my '55 chev and they resisted lead fouling better than the conventional AC. A year or two later Champion came out with the extended tip and I ran them in my '57. They were better than the Autolite and used them in all my V8 cars up into the '60's. Also stocked them in the parts department - for the customers that asked for them. When AC came along with the extended tip I experimented with them but they were not as good as the other two.
As far as durability (eletrode erosion and insulator life) they were all about the same.
The extended tip plugs could cause problems in a 235 . Under heavy service we would find some 235's with a holes burnt through the top of the piston - and they always had an extended tip spark plug installed.

Hi Gene. I was running the AC45 plugs In my 283 engine. A couple months ago, I changed over to the AC45S. In our Tri Five Chevy club, That Is what the other guys are running who have the 283 engines and are happy with the 45S. Almost all the parts stores In the North West carry them.

With todays unleaded gas either one will perfom the same.....thanks to the fact they took the lead out of gas.
Its the best thing that ever happened to gas. The lead caused combution chamber deposits (then the lead melted and splashed on the spark plugs at high temperatures), contaminaded the motor oil causing bearing corrision and caused the ehhaust system to rust out faster.

Gene,
I thought the correct spark plug for a 38 Chevy was the AC46 with the blue Stripes?
Gumshoe

My replies were in reference to what is available in modern spark plugs.
The 1938 spark plugs did have the blue stripe, The book refers to them as blue top.
As far as a correct heat range, that would be determined by the owners driving habbits.
My 1939 parts book lists a Blue Top #44 and #45 for 1933-39 with no mention of a #46. I ould assume the 1938 book would have read the same.
Note that the plug was listed for use back to 1933 but the original number for earlier models was replaced by the above number/description in the parts book as this was the "new and improved" spark plug that was available for replacement.

The January 1938 Parts Book shows PN 1557745 (Blue Top) with no number. Same listing in the September 1938 book. The Aug. 1939 book shows PN 1557745 as (Blue Top No. 46).

My Feb 1, 1939 parts book does not have 1557745 listed in the spark plug group. The price section history shows that number-
Follow this
1555345 says use 1557745 5-1-38
below that it says 1557745 - use 1557746 and 1557747 -10-1-38
There is also a 1557744 that was swirched to the above numbers.
That indicates the two number spark plugs were discontinued in 1939.
The Feb 1, 1940 book has the 1557745 number in the plug group again and is described as a Blue Top #46 - application is 1933-38 (ex CC).Noyt listed for 1939

At one point there was #47 introduced in 1937 but se no farther history of that.

The 1941 book still has the 1557745 plug.

The Nov 1938 Chevrolet Service News describes the changes for 1939 In there it states in the question and answer section "Hoe do the AC-46 spark plugs used in the 1939 engines differ from the Blue Top spark plugs used in the 1938" - answer- The material in the insulation of the new AC-46 spark plugs has been improved so that the plug life is greatly increased over that of the Ac-46 Blue Top. The heat characteristics of the twoplugs are the same"

I believe that there may be more plug info. in the 1939 and 1940 Service News but I haven't
gotten that far yet.

The Chevrolet 216 and 235 engies were always considered "hard on spark plugs"...some brands other than AC would last only a few thousand miles in a Chev and id you were lucky you could get 10,000 from a set of AC.
Todays spark plugs of all brands do much better in these engines.

The little "peanut sized" 10 MM spark plugs used from 1941-48 is long story.

Gene,
I also have not gotten to the Service News yet. Also don't have copy of the Feb. '39 book. This all illustrates the fact that errors and changes in the part books are not rare nor always accurate so additional resources need to be used to verify anything. As I have many times recommended it takes at least three independent Chevrolet and supplier or industry documents to begin to have confidence in any information. This issue appears to be a prime example.

How very true..........

Be thankful that the VCCA judging only requires AC spark plugs....if any one bothers to look.

When I began restoration on a 1940 many years ago, I looked for AC-44 or AC-45 Blue Top Spark Plugs for the car. Why? Because that is what it says in the February 1, 1940 Chevrolet Master Parts Price List. I do not run Blue Tops now even though I have purchased a number of them. I tend to believe that Blue Tops ended production before 1940.
Where do we find documented information on AC Spark Plug changes in design ?

dtm

The best is probably the date code on the end flap on the box containing the plug. Most people don't know but the packaging date is printed on one end box flap. If you don't have the boxes then ????????

The correct plug for a 37 per the owners manual is an AC K-11. Bought 3 sets about 5 years ago from a collector. He my still have these and others for a correct restoration. Down-under 37 Holdens used a Pyrox PZ14