King Vino
10-24-2004, 04:32 PM
Another installment of Erich's FAQ's I hear all this talk about spark plugs, what do all the numbers and letters mean?
Information is from the 1992-93 NGK catalog. There are six fields, some fields are optional and some fields may have multiple letters.
Field: 1 2 3 4 5 6
[B] [CPR] [6] [E] [S] - [11]
Field one: Thread diameter.
A = 18mm
B = 14mm
C = 10mm
D = 12mm
Field two: Construction (optional)
C = hex size 5/8"
K = hex size 5/8 with projected tip (ISO)
M = compact type
P = projected insulator type (Note 1)
R = resistor (Note 2)
SD = surface discharge for rotary engines
U = semi-surface discharge
Z = inductive suppressor
Field three: Heat Range.
2 = hot,
3
4
5
6
7
8
9
10 = cold
Field four: Thread reach (Note 3)
E = 19mm
F = tapered seat
H = 12.7mm (1.5")
L = 11.2mm (7/16")
Field Five: Firing end construction
A, B = special design (no details given)
C = special ground electrode
G = racing use
GV = racing use V type
H = half thread
K = 2 ground electrodes for certain Toyotas
L = half heat range
LM = compact lawn mower type
M = 2 ground electrodes for Mazda rotary engine
N = special ground electrode
P = platinum tip (premium)
Q = 4 ground electrodes
R = delta ground electrode for BMW
S = standard 2.6mm centre electrode
T = 3 ground electrodes
V = fine-wire centre electrode, gold palladium
VX = platinum tip (high performance)
W = tungsten electrode
X = booster gap
Y = v-groove centre electrode
Field Six: (after the dash) Wide gap (optional)
8 = .032"
9 = .036"
10 = .040"
11 = .044"
13 = .050"
14 = .055"
15 = .060"
20 = .080"
--------------------
Notes:
1) The projected insulator simply describes the shape of the plug head. A projected insulator sticks out a little further into the combustion chamber.
2) Resistor plugs are used for two reasons:
· To reduce electrostatic interference
· To provide a sharper "edge" to the voltage spike, which produces a stronger, shorter spark. On high RPM motors, this is important.
3) If field four (thread reach) is blank, an 18mm diameter plug has 12mm reach and a 14mm plug has a 9.5mm (3/8") reach.
The information that our spark plugs must have are B – 14mm. Temp range 7 – 9. H – 12.7mm thread reach. All of the other letters and numbers are not needed. So if you were to buy a B8HS, this will work just as well as a BPR8HS. The difference is price.
Information is from the 1992-93 NGK catalog. There are six fields, some fields are optional and some fields may have multiple letters.
Field: 1 2 3 4 5 6
[B] [CPR] [6] [E] [S] - [11]
Field one: Thread diameter.
A = 18mm
B = 14mm
C = 10mm
D = 12mm
Field two: Construction (optional)
C = hex size 5/8"
K = hex size 5/8 with projected tip (ISO)
M = compact type
P = projected insulator type (Note 1)
R = resistor (Note 2)
SD = surface discharge for rotary engines
U = semi-surface discharge
Z = inductive suppressor
Field three: Heat Range.
2 = hot,
3
4
5
6
7
8
9
10 = cold
Field four: Thread reach (Note 3)
E = 19mm
F = tapered seat
H = 12.7mm (1.5")
L = 11.2mm (7/16")
Field Five: Firing end construction
A, B = special design (no details given)
C = special ground electrode
G = racing use
GV = racing use V type
H = half thread
K = 2 ground electrodes for certain Toyotas
L = half heat range
LM = compact lawn mower type
M = 2 ground electrodes for Mazda rotary engine
N = special ground electrode
P = platinum tip (premium)
Q = 4 ground electrodes
R = delta ground electrode for BMW
S = standard 2.6mm centre electrode
T = 3 ground electrodes
V = fine-wire centre electrode, gold palladium
VX = platinum tip (high performance)
W = tungsten electrode
X = booster gap
Y = v-groove centre electrode
Field Six: (after the dash) Wide gap (optional)
8 = .032"
9 = .036"
10 = .040"
11 = .044"
13 = .050"
14 = .055"
15 = .060"
20 = .080"
--------------------
Notes:
1) The projected insulator simply describes the shape of the plug head. A projected insulator sticks out a little further into the combustion chamber.
2) Resistor plugs are used for two reasons:
· To reduce electrostatic interference
· To provide a sharper "edge" to the voltage spike, which produces a stronger, shorter spark. On high RPM motors, this is important.
3) If field four (thread reach) is blank, an 18mm diameter plug has 12mm reach and a 14mm plug has a 9.5mm (3/8") reach.
The information that our spark plugs must have are B – 14mm. Temp range 7 – 9. H – 12.7mm thread reach. All of the other letters and numbers are not needed. So if you were to buy a B8HS, this will work just as well as a BPR8HS. The difference is price.