Spark Plug X-ref Chart

The following may be "old hat" to a lot of folk, I suspect?  To me it represents a new piece of trivia, in that in 1955 I was all of 9 yrs. young!  All I knew, until I stumbled upon this, was that the "-5" in the spark plug designation had to have some meaning.  However, I had no idea as to what.  That mystery is here revealed —

Spark Plug Cross-Reference Chart from the 1950's






  
  

    
      
14mm Thread x 3/8" Reach 
      

  

    Heat Range
    Champion 
    2-Stroke 
    Suppressor 
    AC 
    Autolite 
    Bosch
    KLG
    Lodge

  

    Hottest 
    
    J-14 
    N/A 
    N/A 
    49, 48 
    ---- 
    W95T1 
    ---- 
    BB14S 

  

    Warmer 
    J-12 
    J12J 
    N/A 
    47, 47Com, 48X 
    A11, AR10 
    W125T1 
    FT20 
    BAN,BS14 

  

    Warmer 
    J-11 
    J11J 
    N/A 
    46-5, 46, 46X 
46Com, 
45-46X 
      		
    A9 
    W145T3 
    ---- 
    BB14S 

  

    Medium 
    J-8 
    J8J 
    XJ8 
    45Com, 45, VF9, 
44-5Com,44-5* 		
    AR8 AT8 A7 AN7 4S-140 
      4S-165 
    W175T4 
    TFS50 
    CAN 

  

    Cooler 
    J-7 
    J7J 
    N/A 
    44, 44Com 
    A5 AN5 AR5 
    W175T4 
    ---- 
    ---- 

  

    Cooler 
    J-6 
    J6J 
    N/A 
    43 43Com 
    AT4 AH4 
    W225T3 
    FS70 
    HAN 

  

    Colder 
    J-5 
    N/A 
    N/A 
    ---- 
    ---- 
    ---- 
    ---- 
    ---- 

  

    Colder 
    ---- 
    J3 
    N/A 
    42-5Com 
    ---- 
    ---- 
    ---- 
    ---- 

  

    Coldest 
      
    J-2 
    N/A 
    N/A 
    42Com 
    A3 AR4 
    W240T3 
    ---- 
    ---- 

  


















Source:  http://www.oldengine.org/members/diesel/Plugs/equiv.htm 




 


Engine                              Normal 
Service                              Hotter 
Plug                                       
Colder 
Plug
                                          
(Original 
Equipment)                     (For 
City-Type 
Operation)              (For 
Continuous Heavy-DutyOperation)
1955 Passenger Car—    AC 44-5* 
                                         
AC 
46-5                                            AC 
43-5 Commercial
 


*Note that spark plugs recommended for use in 
1955 engines are suffixed by a "-5".  This indicates that the 
insulators on these plugs are of the smooth straight shank type , as 
contrasted to the ribbed insulator plugs used for service on later 
engines.


Under no circumstances 
should 1955 style plugs be used in later year cars, as the spark plug boots 
would fit loosely and thus increase the possibility of spark plug flash-over. 





AC Spark Plug Numbering (Example:  AC 44)


· 1st number (4) denotes 
THREAD SIZE      · 2nd 
number (4) denotes HEAT RANGE









  
  

    
      
AC Spark 
      Plug Identification Table 
      - PREFIX

  

    
      
Identification Code 
      

    
      
Description

  

    
      
B

    
      
Series Gap 

  

    
      
C

    
      
Commercial

  

    
      
CS

    
      
Chain Saw 

  

    
      
F

    
      
Fine Line 14 mm 5/8" Hex 

  

    
      
M

    
      
Marine

  

    
      
LM

    
      
Lawn Mower type 

  

    
      
R

    
      
Resistor

  

    
      
S

    
      
Shielded (5/8-24 thread) 

  

    
      
V

    
      
Surface Gap 

  

    
      
Prefixes are sometimes combined e.g., VB, CR 
      




 


Plug Identification Table SUFFIX


ID 
Code 
Description                                                                                         
ID Code Description
A- Cap 
Gap                                                                                                      C- 
Copper Core Center Electrode
C- Colder 
Version of M44 
Plug                                                                         
E- Special Design Electrode Extended Tip
F- 
1/2" (12.7 mm) reach FF 1/2" (12.7 mm) reach, fully 
threaded                     G- Pin Gap (cold-running) I Iridium Center 
Electrode
J- Boot Release Agent, Anti-Seize 
Compound                                                 
K Special Design
L- Long Reach
    7/16" (11.1 mm) reach, (14 mm) 
thread
    3/4" (19 mm) reach, 
(18 mm) thread
    3/4" (19 mm) 
reach, (14 mm) thread (fineline)
LT- Long reach, 
.715" (18.16 mm), Tapered 
Seat                                             M- Special Design Electrode
N 3/4" 19 mm reach, 3/8" 9.5 mm thread 
length                                               R- Resistor (Sport Vehicle Plugs)
S- Extended 
Tip                                                                                               S 7/8"- (22.3 mm) Moderate Long Reach 23/32" (18.25 
mm)
T- 
Tapered Seat Shell 
Design                                                                          TS- Tapered Seat with extended tip
XL- Extra Long Reach, 3/4" (19 mm) fully 
threaded                                         Y- 3-Prong Cloverleaf Electrode
Z- 
Special Gap (usually denotes wide 
gap)                                                      5- .050" (1.3 mm) gap
6- .060" (1.5 
mm) 
gap                                                                                       8- .080" (2 mm) gap 100 Iridium
600- 
Resistor Type 800 Platinum 
Type                                                              900- Double Platinum Type
Suffixes 
are combined to form such AC suffix designations as FG, XLS, TS, FFM, TSX, SZ, 
etc.




 


Heat Range Reference


AC DELCO - The higher the number of the plug, 
the hotter the plug.  Example:  AC 46 is hotter than an AC 44, 
while an AC 43 is cooler.
1955 Cadillac 
use AC 44-5


AUTOLITE - The larger the last digit in the 
part number, the hotter the plug is.  Example:  AR3935 is hotter 
than an AR3932 plug.
1955 Cadillac use 
86 or AP 86 (Platinum)


BOSCH - The lower the number, 
the hotter the plug.
1955 Cadillac use 
WR10FC+


CHAMPION - Typically in the 
same series the larger the number the hotter the 
plug.
Example:  Champion RJ12YC.  
A RJ18YC would be a hotter Champion plug.  A RJ8YC would be colder. 

R = Size
J = 14 mm
12 = Heat 
range
Y = Standard 
Projection
C = 
Copper
1955 Cadillac use 
RJ18YC


DENSO - Like Bosch, the lower 
the number, the hotter the plug.
1955 
Cadillac use W14PR-U


NGK - The larger the number after the dash the 
colder the plug is. Example: R5671A-7 is a colder plug than a 
R5671A-2.
1955 Cadillac use XRG, gapped 
at .045


AC 44 Spark Plug Modern Day 
Replacements


AC R43
Autolite 75 or 85 = AC44S or AC45S (projected tip versions of 
AC44/45)
Accel 137 or 138 projected tip 
(equivalent to AC45S/46S)
Champion J14YC, 
J8C = AC44/45, J11C = AC46 (RJ12YC or RJ14YC for projected 
tip)
NGK XR4 or XR5 or 
B4
Denso W14P-U or 
W9P-U












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Created 4 Jun 2009 
- 06:02:41 Hrs. 


© 2009, G. David Yaros.  All rights 
reserved.