Page 704 - 2017 Racecar Engineering Circle Track 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 CHPJ63Y NGKR5670-7
– – NGKB8S – – – NGKR5670-8
Cold – – – – – – NGKR5670-9
Chevrolet (Big Block), Chrysler (Hemi) - Flat Seat With Gasket
Hot AUTAR3935 CHPC63CX NGKR5671A-7 – – 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 – – CHPV57YC –
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 CHPS57YC NGKR5724-10
Cold - 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.
* Signifies “shorty” style 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. Normal Fuel Fouled Detonation Oil Fouled
• 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 imperative 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 manufacturer. 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.
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