spark plugs, hot vs. cold

Billmc52

Billmc52

Member
I have been reading past posts concerning Champion W18 plugs being hotter than W16Y plugs. I would appreciate some education on the benefit of running hotter plugs vs. colder ones, why use them, what the performance differences may be, how location may make a difference (I live in central Alabama), etc. I am new Model A's and am finding out there is a lot more to operating one than just driving it. I am also really enjoying learning and at the same time finding out how frustrating it can be too. Looking foward to your replies.
 
From what I recall the hot vs cold is in relation to the ceramic insulator temperature. Hotter = keeps the ceramic cleaner which in turn keeps it from conducting. This however can also cause pre-ignition. You want the plug to run as hot as possible without causing pre-ignition. I believe it has to do with the ceramic insulators length and size.

It has NOTHING to do with spark temperature like most think and will not affect power, at least until the plug gets all crudded up and won't fire consistently.
 
The tip of the spark plug gets hot from the sparking and from the combustion it ignites. If it weren't cooled, it would oxidize or otherwise wear away as well as cause preignition. Cooling occurs mainly by thermal conduction down the "nose" of the plug to the cylinder head, which is cooled by the circulating coolant. In a "cool" plug, there is a relatively short, easy path for heat flow from plug tip to the cooling cylinder head threads; in a "hot" plug, the heat conduction has to traverse a longer or more insulated path. Plug position with respect to the hot exhaust gas or cool intake gas valves and swirling combustion chamber turbulence pattern also play a role.

You want the plug to run hot enough to not carbon up but not so hot it wears away prematurely or causes preignition. Also, electrons can more easily jump off of the tip to make the spark the hotter it is.

or something like that

Steve
 
Last edited:
steve s said:
The tip of the spark plug gets hot from the sparking and from the combustion it ignites. If it weren't cooled, it would oxidize or otherwise wear away as well as cause preignition. Cooling occurs mainly by thermal conduction down the "nose" of the plug to the cylinder head, which is cooled by the circulating coolant. In a "cool" plug, there is a relatively short, easy path for heat flow from plug tip to the cooling cylinder head threads; in a "hot" plug, the heat conduction has to traverse a longer or more insulated path. Plug position with respect to the hot exhaust gas or cool intake gas valves and swirling combustion chamber turbulence pattern also play a role.

You want the plug to run hot enough to not carbon up but not so hot it wears away prematurely or causes preignition.

or something like that

Steve
Click to expand...

Thanks Steve, nice explination!
 
While W18's are the closest to 3X, other factors need to be taken into account. A 3X was meant for a stock engine. Many engines today are not stock. A friend has a snyder head on his engine with a Stipe 330 cam. The W16's were pre igniting with crusty white insulators, mileage was good (18mpg) but the engine was not as smooth as we wanted. He thought it was running too lean and changed the carburetor with no difference in performance. A switch to C14's ( modern plug would be W14) gave a smooth idle, tan insulator , smoother power and 19MPG on a long tour. High compression heads have a faster and hotter burn, so a cooler plug just might be what they need.

the following was posted by LArry Brumfield:

HOTTER DOWN TO COLDER - Spark Plugs



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 (562)
W89D (589 TT15 )
W16Y (561)
C95F (595)
W20 (520 )
W14 (3076 TT10 )
W10
W85N
W80N

NOTE: Highlighted items were added by me:

5XX are new Champion numbers from local CarQuest.
3076 is Autolite
TTxx are Motocraft

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


Larry B.


Here is what Vince Falter said about the C16C plugs:

Re: Champion C-16C


Posted by forever4 from 19.65.33.58.broad.xw.sh.dynamic.163data.com.cn (58.33.65.19) on Tuesday, June 02, 2009 at 6:59AM :

In Reply to: Re: Champion C-16C posted by Barry from ? (67.133.62.42) on Monday, June 01, 2009 at 7:19PM :

Yep, My results vary. My experience with many C16C years ago is that they are way too cold and easy to foul and very troublesome.
 
Purdy Swoft said:
If you look at Ahooga, Larry Brumfield now says, on monday september 18 that Champion W-18 is hotter than W-16-Y
Click to expand...

John Stone said:
W18's are about as close to the 3X as you can get.
Click to expand...

So the W16Y plugs I am running seem to be sooty but dry when I check them. It seems that maybe I should try the W18 plugs since they are hotter and similar to the 3X and see how they look after I put some miles on them. This seems like it is a trial and error situation to find the best plug for a specific engine. Am I on track here?
 
The Champion heat range chart shows the Champion W-16-Y to be 6. The chart shows the W-18 to have a heat range of 7 . Brumfields information was incorrect. If you click on the link that Hoarse Whisperer offered in his post you can read what my arguement was. Besides my personal experience with both spark plugs the Champion heat range charts hold out what I said. Brumfield would make up anything at the time in an effort to discredit me. Now if you go over to Ahooga you will see where he now says that the W-18 is hotter. I won't waste my time argueing the point. Ignorance usually prevails.
 
yes, you could. or try leaning your carb out, get better mileage.

dry soot is fuel. wet soot is oil.
 
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