Spark Plug Recommendations and Gap
3800 (L36 SII NA, L67 SII Supercharged)
L67/L32 SC: Stock or lightly modified, TR55/TR55IX, TR6/TR6IX, Autolite 103/104 gapped at .055”
NA 3800: NGK TR55/TR55IX gapped at .056”
Turbo/Highly modified: Autolite 103 or TR6/TR6IX .045-.050”
LNF / LHU (2008-2010 Cobalt SS-TC / 2008-2010 HHR SS / Sky Redline / Solstice GXP):
ACDelco OEM GM plugs ONLY. No NGK or other brands as they cause misfires and do not run correctly. Come pre-gapped at .032
Above 500whp you can run the Denso race plugs we offer. also should be gapped .032-.035
LSJ (2005-2007 Cobalt SS-SC / 2004-2007 Ion Redline):
Supercharged BKR7e gapped at .035 for most setups.
Turbo on 91-93: BKR8EIX iridiums for the best for performance.
Turbo on e85 BKR7e gapped (tighten gap as boost goes up) rule of thumb is as large as you can go without breaking up.
Sonic/Cruze 1.4 (Sonic 1LS, 1LT, 1LZ/LTZ, RS | Cruze 1LT, Eco, 2LT, LTZ, RS):
BKR7e gapped at .028”
LTG (2.0 Camaro 1LS, 1LT, 2LT, RS / 2.0 ATS Base, Luxury, Premium, Performance):
OEM ACDelco iridiums or even better Denso iridium ITV24. Gap to 0.035 on stock tune, and 0.032 if tuned.
2.2/2.4 (Cobalt LS, LT, Sport / Ion 1, 2, 3 / Solstice & Sky NA):
2.2: LTR6IX-11 (NA or boosted), 0.040 gap.
2.4: XP5263 (NA or boosted)
Polaris Slingshot (S, SL, SLR, SLR LE):
NA: Remain with the OEM plugs only
Boosted: ACDelco 41-108. The Slingshot tends to idle and perform well overall and have a life with these plugs installed. The gap is .032 if under 20psi. If boost is 20psi or more, close the gap to .028
Gap Conversion Chart and Warning
***When adjusting the gap on your spark plugs, never pry, apply or exert any force on the spark plug center electrode, or center electrode ceramic insulator. Only force the ground electrode arm to the desired location, further away or closer to the center electrode. You should not adjust spark plug’s gap more than 3 times, and never exceed .008” increment of adjustment. Either of these will weaken the ground and could lead to it breaking inside of your block.
Spark Plug Gap Basics
In the simplest terms, the spark plug “gap” is referring to the closest point between the spark plug center electrode and the spark plug ground electrode. Spark will travel between the slight gap, igniting in your engine cylinder. The larger the gap setting on the spark plug, the higher voltage required for the spark to jump between the contact points. Larger gaps are usually more desirable in late model engines due to their high output ignition coils, and also lower compression naturally aspirated engines. You can get away with a larger gap in an N/A set up because the cylinder pressure is relatively low, reducing your chances of spark blowout.
Onto our favorite types of motors here at ZZP – forced induction. More specifically, any engine with higher cylinder pressure. This can include high compression builds, turbochargers, supercharged, and nitrous applications. Almost all boosted set ups require a spark plug gap smaller than .032”. The increased cylinder pressure and dense A/F mixture makes it much harder for spark to penetrate. Therefore, higher voltage and a smaller spark plug gap will make your engine much happier, and safer. We often see this multiply exponentially with power, and it isn’t uncommon to see 1000hp+ vehicles running a gap as small as .016”. Another example is ProMod turbo cars, which are boosted and running M1 Race fuel. These guys, even with their custom high output ignition systems making upwards of 60,000 volts (high current & mJpower output) run a gap as small as .012.
Copper VS. Iridium Plugs
You aren’t the only one. Many get stuck at the difficult decision deciding between these two types of plugs. Spark plugs have a vast range of construction, just in metals alone you can find aluminum, iridium, platinum, copper, and more. Copper core spark plugs are still the most common. Metal in the spark plug really serves one job: to channel electric energy from the plug wire through the spark plug, so it can be forced to the engine block in the form of a spark. This is why any conductive metal can technically do the job. A byproduct of this is heat, and different metals deal with heat better or worse than others. Copper plugs are considered to have the best performance, as copper is the most conductive metal. Platinum and Iridium are more likely to overheat, also. However, Iridium and platinum plugs do not deteriorate as fast as copper, so your spark plugs will run longer in your engine without needing to be changed. On a good set up you can expect your copper plugs to last 20,000 miles without affecting performance (natural driving conditions), but Iridium and platinum can go up to twice this, assuming your car is tuned well, and in natural driving conditions.
When to Replace or Gap your Spark Plugs
Let’s talk about what we do best: Making power. Using an optimal spark plug for your application will get the most out of your set up, and often makes more horsepower difference than people assume. This also goes for used spark plugs, and often you can see cars making up to 20HP by just replacing their old, used, and worn out units. Used plugs will not retain their set gap as well, degrade the insulating properties, and get gummed up by combustion deposits and old fuel saturation. These factors will rob voltage in your system, and prevent your car from being as fast as you built it to be.
We select our recommended plugs extremely carefully, and also test optimal gap settings until they are just right. To measure for the best engine and spark plug performance, we look at the following parameters: Potential of the ignition system and spark voltage, pressure in the combustion chamber at the time of spark discharge, type and concentration of the fuel, engine ignition timing advance, engine load and intended use, and the type of ignition system itself.
Spark Plug Heat Range
You may have heard spark plugs referred to as “colder” or “warmer” sets. This is an especially common phrase if you hang out with tuners all day like we do. The “temperature” of the spark plug, or the “heat range” is a measure of how fast the spark plug tip dissipates combustion heat. Spark plugs are engineered to stay cool enough to avoid pre-ignition, avoid detonation and electrode destruction. But they also need to be hot enough to burn off combustion deposits, which leads to fouling, and even worse, misfires.