Page 673 - 2018 Racecar Engineering Drag Racing Parts and Accessories Catalog

Spark Plug Heat Range/Cross Reference
Thread Heat Standard Non-Resistor Spark Plugs Power/Projected Tip Non-Resistor Spark Plugs
Size/Reach Hex Range Autolite Champion NGK Accel Autolite Champion NGK
Chevrolet, Chrysler (Wedge), Oldsmobile, Pontiac - Standard Reach - Flat Seat With Gasket
Hot — — — — — — NGKR5670-5
— — NGKB6S — AUTAR73 — NGKR5670-6
14mm/3/8" 13/16" AUT353 CHPJ4C NGKB7S — AUTAR72 — NGKR5670-7
— — NGKB8S — — — NGKR5670-8
Cold — — — — — — NGKR5670-9
Chevrolet (Big Block), Chrysler (Hemi) - Flat Seat With Gasket
Hot AUTAR3935 CHPC63CX NGKR5671A-7 — AUTAR3912 CHPC63YC —
AUTAR3934 CHPC61CX NGKR5671A-8 — AUTAR3911 CHPC61YC NGKR5672A-8
14mm/3/4" 5/8" AUTAR3933† CHPC59CX NGKR5671A-9 — AUTAR3910 † CHPC59YC NGKR5672A-9
AUTAR3932† CHPC57CX NGKR5671A-10 — — CHPC57YC NGKR5672A-10
Cold AUTAR3931 CHPC55CX NGKR5671A-11 — — — —
Chevrolet (Big Block), Chrysler (Hemi) - Flat Seat With Gasket
Hot — — — — — — NGKBP5ES
AUTAR2593 — — — — — NGKBP6ES
AUTAR2592 — — — AUTAR53 — NGKBP7ES
14mm/3/4" 13/16"
— CHPN59DR — — AUTAR52 CHPN59YDR —
— CHPN57DR — — AUTAR51 — —
Cold — — — — AUTAR50 — —
Chevrolet (Small Block), Ford (Small Block) - Conical/Tapered Seat
Hot — — — ACL0276S-4* — — —
— — NGKR5673-6 — — — NGKR5674-6
AUTAR135 CHPV63C NGKR5673-7 — AUTAR13 — NGKR5674-7
14mm/.460" 5/8" AUTAR134 — — — AUTAR12 — NGKR5674-8
AUTAR133 — NGKR5673-8 — — — NGKR5674-9
AUTAR132 CHPV59C NGKR5673-9 — — CHPV59YC NGKR5674-10
Cold — CHPV57C NGKR5673-10 — — — —
Chevrolet (Big Block), Ford - Conical/Tapered Seat
Hot — — — — — CHPRS9YC —
— — — — AUTAR94 — NGKR5724-8
14mm/.708" 5/8" AUTAR474 CHPS59C — — AUTAR93 CHPS59YC NGKR5724-9
AUTAR473 CHPS57C — — AUTAR92 — NGKR5724-10
Cold AUTAR472 CHPS55C — — — — —
Ford (Windsor and Big Block) - Conical/Tapered Seat
Hot — — — — AUTAR33 — —
18mm/.460" 13/16" — — — — AUTAR32 — 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 (fl at) 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
Normal Fuel Fouled Detonation Oil Fouled
temperatures.
• Stay with the same plug type after fi nal heat range selection unless major modifi cations have been made (increasing the horsepower or operating range).
Spark Plug Heat Range Tech
A spark plug’s Heat Range, defi ned 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 fi ring tip. A plug that is excessively cold or hot for the application in question will eventually cause the engine
to misfi re. When working with an engine that is stock or mildly modifi ed, 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 misfi re, 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.

671