Blog Tuning Spark Plug Heat Range - Where do I start?

Spark Plug Heat Range - Where do I start?

Spark plugs with the proper heat range make a world of difference in the final outcome of the tune.  If the spark plug heat range is too hot the plug cannot dissipate heat quickly enough and you'll have a source of pre-ignition in the engine.  Earlier we published an article about how to read spark plugs.  You can read that article by clicking here. Even if you know how to read plugs, this article will give you a rough idea on where to start.

The strongest correlation to spark plug heat range is BMEP or MEP which both can be found as a function of horsepower and displacement or torque and displacement.  What we did is plotted RWHP/Displacement (CID) against the heat range we found to be appropriate to nine different engines.  While I do not expect the results to be linear the correlation is fairly strong. Also we took all the examples as approximate RWHP as tested on a dynojet dyno.   Do not think that what we did here can be taken as the Bible, but do use it as an approximate starting spot.  Follow our other article How to Read Spark Plugs to fine tune the proper heat range plugs in your application.

To find the starting heat range plug for your application....

  1. Determine approximate RWHP expected
  2. Divide RWHP by displacement in CID.  For example 430 RWHP / 376 CID = 1.14
  3. Multiply result found in (2) by 3.07 - Continuing example - 1.14 * 3.07 = 3.5
  4. Add 3.15 to result found in (3) - Continuing example - 3.5 + 3.15 = 6.65
  5. Round result found in (4) up!  So suggested starting heat range is 7

 

Heat Range vs. Power/CID

 

Spark Plug applicatoin and part numbers.  Credit goes to Mike@HSW. Can be found on LS1tech here

http://ls1tech.com/forums/nitrous-oxide/1159392-too-much-advertising-not-enough-tech-spark-plug-reference.html

Taper Seat - .708 - .75" reach - 14mm thread dia. - 5/8 hex
Fittment - LSx & LTx w/ taper seat plugs - Mod Ford (96-04 SOHC 4.6)(96-01 DOHC 4.6)(03-04 SC DOHC 4.6)*(99-04 SC SOHC 5.4)* - 5.0L Ford (91-95 w/ taper seat heads)
* - Supercharged Mod Fords start at 6 for stock heat range.

Heat Range Brand Part Number Design Number Tip Designation Special Notes
5 NGK 3951 TR55 Projected Stock Heat Range. Extended Gap.
5 NGK 7164 TR55IX Projected Stock Heat Range. Extened Gap. IRIDIUM.
5 (NGK) Denso 5325 IT-16 Projected Sotck Heat Range. IRIDIUM.
5 (NGK) AC Delco R42CLTS6 R42CLTS6 Projected Stock Heat Range. Extended Gap.
5 (NGK) Champion 13 RS14YC6 Projected Stock Heat Range. Extended Gap.
5 (NGK) Denso 5023 T16EPR-U15 Projected Stock Heat Range. Extended Gap.
6 NGK 4177 TR6 Projected 1 step colder w/ projected tip.
6 NGK 3689 TR6IX Projected 1 step colder w/ projected tip. IRIDIUM.
6 NGK 3177 BR6EF Non-Projected 1 step colder w/ NON-projected tip.
6 (NGK) Denso 5326 IT-20 Projected 1 step colder w/ projected tip.
6 (NGK) Champion 304 RS9YC Projected 1 step colder w/ projected tip.
6 (NGK) Autolite AR103 AR103 Projected 1 step colder w/ projected tip.
7 NGK 3690 TR7IX Projected 2 steps colder w/ projected tip. IRIDIUM.
7 NGK 3346 BR7EF Non-Projected 2 steps colder w/ NON-projected tip.
7 (NGK) Denso 5040 T22EP-U Projected 2 steps colder w/ projected tip.
7 (NGK) Denso 5327 IT-22 Projected 2 steps colder w/ projected tip. IRIDIUM.
7 (NGK) Brisk 51 GR14S Non-Projected 2 steps colder w/ NON-projected tip.
8 NGK 3691 TR8IX Projected 3 steps colder w/ projected tip. IRIDIUM.
8 NGK 1049 B8EFS Non-Projected 3 steps colder w/ NON-projected tip. Non-Resisted.
8 NGK 7317 R5724-8 Projected 3 steps colder w/ projected tip. Non-Resisted
8 (NGK) Denso 5328 IT-24 Projected 3 steps colder w/ projected tip. IRIDIUM.
8 (NGK) Champion 281 S63YC Projected 3 steps colder w/ projected tip. Non-Resisted.
8 (NGK) Autolite AR474 AR474 Non-Projected 3 steps colder w/ NON-projected tip. Non-Resisted.
8 (NGK) Brisk 84 GR12S Non-Projected 3 steps colder w/ NON-projected tip.
9 NGK 1085 B9EFS Non-Projected 4 steps colder w/ NON-projected tip. Non-Resisted.
9 NGK 7891 R5724-9 Projected 4 steps colder w/ projected tip.
9 (NGK) Denso 5329 IT-27 Non-Projected 4 steps colder w/ NON-projected tip. IRIDIUM
9 (NGK) Champion 286 S61C Non-Projected 4 steps colder w/ NON-projected tip. Non-Resisted.
9 (NGK) Champion 280 S61YC Projected 4 steps colder w/ projected tip. Non-Resisted.
9 (NGK) Autolite AR473 AR473 Non-Projected 4 steps colder w/ NON-projected tip. Non-Resisted.
9 (NGK) Brisk G10S G10S Non-Projected 4 steps colder w/ NON-projected tip. Non-Resisted.
10 NGK B10EFS B10EFS Non-Projected 5 steps colder w/ NON-projected tip. Non-Resisted.
10 NGK 5980 R5724-10 Projected 5 steps colder w/ projected tip.
10 (NGK) Brisk G08S G08S Non-Projected 5 steps colder w/ NON-projected tip. Non-Resisted.
10 (NGK) Champion 683 S59C Non-Projected 5 steps colder w/ NON-projected tip. Non-Resisted.
10 (NGK) Champion 685 S59YC Projected 5 steps colder w/ projected tip. Non-Resisted.
10 (NGK) Autolite AR472 AR472 Non-Projected 5 steps colder w/ NON-projected tip. Non-Resisted.
10.5 (NGK) Champion 682 S57C Non-Projected 5.5 steps colder w/ NON-projected tip. Non-Resisted.
11 (NGK) Champion 681 S55C Non-Projected 6 steps colder w/ NON-projected tip. Non-Resisted.

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