HOTTER DOWN TO COLDER - Spark Plugs

[Larry Brumfield]

For those who may be interested, the following 7/8"-18 spark plugs will fit the Model A and were available as of a few years back. They are also not all the ones that I know of.

Champion (hotter down to colder):

W95D
W89D
W16Y
W20
W18
W14
W10
W85N
W80N

Also the original 3X and W18 which Champion lists as norm. Also according to Champion, the W16Y is hotter than the W18 at low speed but cooler at high speeds over 5500 RPM....(over 5500 RPM? ... maybe Speedy ED J, Pete, George Miller, Dennis Pierce would be interested... maybe even Brent)

Motorcraft (hotter down to colder):

TT15 (the same as Champion W89D)
TT10 (the same as Champion W14)
TT8 (the same as Champion W14)
TT4 (the same as Champion W10)

Autolite:

3076 (the same as Champion W14 and Motorcraft TT10)

Mopar (hotter down to colder):

P-9-7S
P-9-6S
P-9-5S

Prestolite (hotter down to colder)

78-10
78-8

Stitt (hotter down to colder)

137 BSP
197
147 B
13/10

Range is a key word when one speaks of heat range.

Reading these Champion numbers is not real difficult. For example, W20 or W18, etc.:

The W is the shell design and it always means 7/8-18.

I should also add that Champion has made changes over time. For example a C-16C, used in many a Model A, starts with a C, BUT it is a 7/8-18 plug. It was discontinued about 1979 and replaced by the W16Y. There are many like this.

The number is the heat range and the lower the cooler (unless other letters immediately follow, like Y for example, which depending on the letter or letters can change or affect the heat range):

1- 25 = Automotive and small engines

25 - 50 = Aviation

51 - 75 = High Performance

75 - 99 = Industrial and Special Applications


Larry B.

[1931 flamingo]

Thank you very much for this chart.
Paul in CT

[Karl]

Thanks Larry

Now I get confused (generally easy!) Hotter plus for cars that normally travel at faster speeds. Colder for those who do lots of short runs ?? -Karl

[Rem/Mo]

Originally Posted by Karl

Thanks Larry

Now I get confused (generally easy!) Hotter plus for cars that normally travel at faster speeds. Colder for those who do lots of short runs ?? -Karl

I think you have it backwards.

If you run your car hard the plugs will naturally run hotter so a colder plug would be preferred to keep plug tip temps down.

On short runs a hotter plug would help get tip temps up and help prevent fouling.

[[email protected]]

Thanks much for the plug chart
cheers

[Kevin - Illinois]

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Man Larry, more great information. Sure is nice seeing your posts!

[Art Bjornestad]

Boy, what a valuable list!!! I often wondered how the plugs stacked up heat wise. Thanks, Art

[Jim/GA]

Wow, this is really helpful.

Are Motorcraft TT10 and TT8 both equivalent to the Champion W14? Seems odd.

Where in the long Champion list does the original 3X (and W18) fall? Between which 2 other plugs?

[Larry Brumfield]

Originally Posted by Jim/TX

Wow, this is really helpful.

Are Motorcraft TT10 and TT8 both equivalent to the Champion W14? Seems odd.

Where in the long Champion list does the original 3X (and W18) fall? Between which 2 other plugs?

"Are Motorcraft TT10 and TT8 both equivalent to the Champion W14? Seems odd."


Why does this seem odd? The Champion W14 obviously has a wider heat range. Range is a key word when one speaks of heat range.

The W18 is below the W20. I don't know why I didn't put it on the chart. I'll add it.

Reading these Champion numbers is not real difficult. For example, W20 or W18, etc.:

The W is the shell design and it always means 7/8-18

I should also add that Champion has made changes over time. For example a C-16C, used in many a Model A, starts with a C, BUT it is a 7/8-18 plug. It was discontinued about 1979 and replaced by the W16Y. There are many like this.

The number is the heat range and the lower the cooler (unless other letters immediately follow, like Y for example, which depending on the letter or letters can change or affect the heat range):

1- 25 = Automotive and small engines

25 - 50 = Aviation

51 - 75 = High Performance

75 - 99 = Industrial and Special Applications


Larry B.

[Purdy Swoft]

Larry, I allways read your posts . I beg to differ on the heat of a couple of the mentioned Champion plugs. I'm not saying this for the hell of it. I believe from my experience that the W18 is hotter than the W16Y. If the W16Y is hotter than the W18 can you explain why the W16Y plugs that I tried to get by with for years in several of my model A's were always black and sooty and when I changed to the W18 the problem was solved. How could a colder plug run cleaner at speeds of mostly 50 mph and less. It has been my lifetime belief and still is that the higher the rpm the hotter the spark. That is why a colder spark is used in race cars that are mostly running at full throttle to keep from melting pistons.

[Bruce Lancaster]

So a W18 is equivalent to a 3X? How does a 4X fit in? Ford literature seems to suggest this as a broad-range plug, and it eventually became the replacement plug for fours.

[Purdy Swoft]

Bruce, It is my mind set or belief that the W18 spark plug was the same heat range and was the replacement for the C4 that was the standard spark plug for the 32 -34 four cylinder engines. The higher compression of the B or 32-34 four cylinder engines needed a hotter spark plug. It was thought that the higher compression would blow out the spark an a closer gap of .032 was recommended with the C4 plugs. I have several nos C4 plugs and this is the recommendation iincluded with each plug. When the two piece C4 plug was discontinued the W18 was the replacement. I have found that the C4 or W18 run very clean in any of my model A's, high compression head or not. It is also my belief that the 3X plug has the same heat range as the discontinued C16C that was the replacement plug for the 3X. Opinions are all over the place about heat range. My experience tells me that W18 is the best choice for the average model A driver. I refuse to use a spark plug that runs sooty no matter what anybody says.

[Bruce Lancaster]

I need to refresh my memory of the relevant '32 or '33 bulletin, but Ford said something similar to what you said and I think made the C4 the service replacement for the A...
Again from my leakiy memory, I think the B started production with the C3 then picked up the C4 during 1932 direct from the V8 line.

[Purdy Swoft]

Bruce, I think you are correct that the first service replacement for the 3X was the C4 when the C4 was no longer made the replacement for the 3X became the C16C . I'm not familiar with the C3. I don't think that the C4 was ever used in the V8. Ithink the early V8 used an 18mm plug instead of the 7/8 plugs.

[Larry Brumfield]

Originally Posted by Purdy Swoft

Larry, I allways read your posts . I beg to differ on the heat of a couple of the mentioned Champion plugs. I'm not saying this for the hell of it. I believe from my experience that the W18 is hotter than the W16Y. If the W16Y is hotter than the W18 can you explain why the W16Y plugs that I tried to get by with for years in several of my model A's were always black and sooty and when I changed to the W18 the problem was solved. How could a colder plug run cleaner at speeds of mostly 50 mph and less. It has been my lifetime belief and still is that the higher the rpm the hotter the spark. That is why a colder spark is used in race cars that are mostly running at full throttle to keep from melting pistons.

The experience you described is not the same as my experience with the W16Y........ I'm not sure why some people get different results. There are too many variables which can affect a spark plug.

At the same time I'm not prepared to dispute the Champion engineers! ......... Reminds me of people telling me what is best for a Brumfield Head when I know different.

According to the Champion engineers, a spark plug with a projected nose (like the W16Y, the Y stands for standard projected nose) has a broader heat range. The core nose is longer and projected into the chamber with open exposure which provides a "hotter" plug at low speed and helps to prevent fouling.

As the engine speed increases, the incoming air/fuel mix flows across the exposed tip of the core nose, providing charge cooling which effectively reduces heat range at higher speeds.

Of course higher speed to Champion is over 5500 RPM!

Now explain why you think the intensity of the spark ITSELF gets hotter the higher the RPM .... and how the spark itself would get a plug hot enough TO GLOW and cause pre-ignition?

The spark just lasts for an instant....

It's the compression, combustion heat and high cylinder pressures that heat up the spark plug.


Larry B.

[Bruce Lancaster]

1932 V8 only used the 7/8" plug.

[Purdy Swoft]

Bruce, you've got me there. The earliest V8 that I have owned was a 37.

[david801]

What should the spark plug gap be on the newer style plugs like the Motorcraft TT10?

[Larry Brumfield]

Originally Posted by david801

what should the spark plug gap be on the newer style plugs like the motorcraft tt10?

.032"

[Kirby1374]

I just purchased a set of W18's. I have c16c's in the motor now. the W18's are bigger in size. Did I get the right plugs?