AC spark plug type code

[Uncle-Pekka]

AC44 plug works well in a flathead engine, but...

What do the prefix & suffix letters stand for?

E.g. R44SX appears commonly for sale at eBay.

[TodFitch]

AC44 plug works well in a flathead engine, but...

What do the prefix & suffix letters stand for?

E.g. R44SX appears commonly for sale at eBay.

R44SX would be a resistor plug (the R) and, I think, an extended tip (S). No idea on the X. The first 4 indicates 14mm threads and the second 4 indicates the heat range.

But a AC 44 for a Plymouth L-6 engine?

Hmmm. I've run Champion J-11 forever in my 1933. Well not actually forever, just since 1973. I know that Champions now have a bad rap. And I'll most likely use AC plugs on the next tune up.

But it looks like the AC equivalent to a J-11 is the AC 46. See http://www.oldengine.org/members/diesel/Plugs/equiv.htm

A AC44 would be a cooler heat range than my car seems to work well at. I've got a low compression engine compared to you all so maybe that makes a difference. But what AC plugs have people been running 44, 45, 46 or what?

[Don Coatney]

[Uncle-Pekka]

R44SX would be a resistor plug (the R) and, I think, an extended tip (S). No idea on the X. The first 4 indicates 14mm threads and the second 4 indicates the heat range.

A AC44 would be a cooler heat range than my car seems to work well at. I've got a low compression engine compared to you all so maybe that makes a difference. But what AC plugs have people been running 44, 45, 46 or what?

Heat range must be considered.

What about the resistor? Is it an issue with the D24 ignition system, where resistor is not required?