Spark Plug Heat Range/Cross Reference Thread Size/Reach Hex Heat Range Autolite
Standard Non-Resistor Spark Plugs
Power/Projected Tip Non-Resistor Spark Plugs
Champion
NGK
Accel
Autolite
Champion
NGK
Chevrolet, Chrysler (Wedge), Oldsmobile, Pontiac - Standard Reach - Flat Seat With Gasket
Hot
— — — —
— — — —
—
—
—
— NGKR5670-5 — NGKR5670-6 — NGKR5670-7 — NGKR5670-8 — NGKR5670-9
NGKB6S NGKB7S NGKB8S
— AUTAR73 — AUTAR72
14mm/3/8"
13/16"
AUT353
CHPJ4C
— —
— —
Cold
—
Chevrolet (Big Block), Chrysler (Hemi) - Flat Seat With Gasket
Hot
AUTAR3935 AUTAR3934 AUTAR3933 † AUTAR3932 † AUTAR3931
CHPC63CX CHPC61CX CHPC59CX CHPC57CX CHPC55CX
NGKR5671A-7 NGKR5671A-8 NGKR5671A-9 NGKR5671A-10 NGKR5671A-11
— AUTAR3912 — AUTAR3911 — AUTAR3910 †
CHPC63YC CHPC61YC CHPC59YC
—
NGKR5672A-8 NGKR5672A-9 NGKR5672A-10
14mm/3/4"
5/8"
— — — —
— CHPC57YC
Cold
—
—
—
Chevrolet (Big Block), Chrysler (Hemi) - Flat Seat With Gasket
Hot
—
— — —
— — — — — —
— —
— — — — —
NGKBP5ES NGKBP6ES NGKBP7ES
AUTAR2593 AUTAR2592
— AUTAR53 — AUTAR52 — AUTAR51 — AUTAR50
14mm/3/4"
13/16"
— CHPN59DR — CHPN57DR
CHPN59YDR
— — —
Cold
—
—
Chevrolet (Small Block), Ford (Small Block) - Conical/Tapered Seat
Hot
— —
—
— ACL0276S-4*
— —
—
—
— NGKR5673-6
—
— NGKR5674-6 — NGKR5674-7 — NGKR5674-8 — NGKR5674-9
AUTAR135 AUTAR134 AUTAR133 AUTAR132
CHPV63C
NGKR5673-7
— AUTAR13 — AUTAR12
14mm/.460"
5/8"
—
—
— NGKR5673-8
— — —
—
CHPV59C CHPV57C
NGKR5673-9 NGKR5673-10
— CHPV59YC
NGKR5674-10
Cold
—
—
—
—
Chevrolet (Big Block), Ford - Conical/Tapered Seat
Hot
— —
— —
— — — — — — — —
—
— CHPRS9YC
—
— AUTAR94 — AUTAR93 — AUTAR92
— NGKR5724-8
14mm/.708"
5/8"
AUTAR474 AUTAR473 AUTAR472
CHPS59C CHPS57C CHPS55C
CHPS59YC
NGKR5724-9
— NGKR5724-10
Cold
—
—
—
—
Ford (Windsor and Big Block) - Conical/Tapered Seat
Hot
— — —
— — —
— AUTAR33 — AUTAR32
— — —
—
18mm/.460"
13/16"
NGKAP8FS
Cold — Important Note: Use cross reference chart as a guide only. Due to differences in design and material, plugs listed in cross reference are not exactly alike. * “Shorty” spark plug. † Special Autolite Racing “X” style electrode spark plug, which alleviates piston/spark plug clearance issues, is also available; add “X” to end of part number. — —
Spark Plug Diagnosis
Pictures Courtesy Of Autolite
• Determine the thread diameter, length (reach) and whether tapered or gasket (flat) seat. • Select gap style. • Select heat range. • Adjust fuel mixture and spark advance timing for maximum performance. • Inspect plugs and pistons for evidence of detonation, abnormal combustion or excessive temperatures. • Stay with the same plug type after final heat range selection unless major modifications have been made (increasing the horsepower or operating range). Spark Plug Heat Range Tech A spark plug’s Heat Range, defined as the measure of how fast the tip of the plug dissipates combustion heat, can range from as low as 500°F to as high as 2,500°F. Manufacturers offer plugs in many heat ranges, from cold through medium hot, to very hot. It is impera- tive that the plug stay cool enough to prevent pre-ignition or electrode destruction, and still remain hot enough to burn off combustion deposits that form at the firing tip. A plug that is excessively cold or hot for the application in question will eventually cause the engine to misfire. When working with an engine that is stock or mildly modified, it is often best to use the plug recommended by the car manu- facturer. However, if the compression ratio has been altered, a different heat range plug may be required. Many racers rely upon their engine builder for plug heat range recommendations. If a racer is unsure of the correct heat range to use, it is always recommended to “stay on the safe side” and use a colder plug. A switch in heat range can change the temperature of the spark plug tip by 70-120°F. If the plug selected is too cold, it will eventually foul and misfire, but it will not damage the engine. A plug which is too hot can cause pre-ignition and detonation, often resulting in a severely damaged engine. Normal Fuel Fouled Detonation Oil Fouled
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