Best Spark Plugs for heavily modded GTP - NGK's?

[CNorell145]

Hey everyone,

I am looking to get new spark plugs, and was recommended to get NGK's Iridium IX plugs. Does anyone have any experience with these they would like to share? Or have another recommendation?

Current performance mods:

2.5" intercooler
Radical cam
Ported throttle body
42.5# injectors (not 100% sure these are sufficient - would love some input on this as well)
2.8" SC pulley
Headers/exhaust (cat deleted)
Engine block swapped from stock GTP to stock NA (slightly higher compression ratio)
Ported intake manifold
Hot air intake (open cone in bay)

If it matters, I run 93 octane fuel from BP, and don't care much about fuel economy.

Also, at what point do you need to upgrade your fuel pump? I'm fairly certain mine is still stock - will check sometime this weekend to be sure.

Thank you in advance.

[Fivefingerdeathpunch]

Whatever you pick is going to need to be at least 2-3 heat ranges cooler than factory with a gap near .025-.030 to prevent spark blow out. Most run copper core plugs for the cheap cost and the fact that they are great with a boost and the waste spark ignition system. Auto Lite 103's are pretty popular, not sure what number the Iridium NGK's are. Maybe find out what the CTS-V or ZR1 covettes run, as those are a few steps cooler than the NA spark plugs. NGK BR6EF/BR7EF are another choice.

Get a fuel pressure gauge on there, if pressure is dropping you are out of pump. To be on the safe side I think a 255 LHP pump would be a good idea right about now.

[CNorell145]

The NGK iridium IX has a .6mm (.0236 inch) gap, although I have no idea what their heat range would be...

Noob question - when talking about the temperature of a spark plug, are we talking about how hot the spark itself is?

[SgtMarshal]

I'm running autolite 104's on my 2001 gtp. it has a 2.6 pulley, methanol injection, E85 and an xp cam

[coolone]

Credit: Overkill...


Spark Plugs

A spark plug has two jobs. One is to fire the cylinder its installed into. Second is to remove heat and maintain a proper operating temperature in the cylinder, which many people don�t realize.
All 3800 Supercharged engines run too hot a spark plug. They run the same very hot plug that the non-supercharged 3800 run and even those are hotter than most other GM V8s for example. Even fully stock with a stock pulley, it is my strong recommendation to drop one heat range, to an NGK TR5 or other plugs that you can spec from a GM Vortec/LS1/2/3 V8. When running a smaller supercharger pulley such as a 3.5/3.4/3.2, its my recommendation to go two heat ranges lower, to an NGK TR6 or Autolite 104 for example. If you�re running a full supercharger build with a 2.55� pulley or a turbo setup with more than 15psi of boost, you can now step down again to NGK TR7s or Autolite 103s, however this step is only beneficial on extreme setups, I would stick with 2 range colder on the majority of setups and ensure your intercooler is doing its job to remove heat from the boost.

Copper plugs have a wider centre electrode and they will run cooler than the sharp thin pointed Iridium plug centre electrode. This can lead to reduced engine knock. They will erode faster though, and require replacement or regapping every year. Run copper plugs only if you truly mean to take care of them, they are not a set and forget installation.

Speaking of gapping, it�s my firm belief that most run too wide a spark plug gap. Factory gap is an outrageous .060� and the ignition system is strong enough to handle it. However on supercharged 3800s I recommend a gap of .050� on stock pulleys and .045� most smaller pulley setups. Full bore setups with 2.x� pulleys should run a .040� gap. Minute misfires that you may not be able to fully feel can show up as KR on a scantool and closing the gap can reduce this KR when it occurs. This is contrary info to what you read on the internet forums but this is a lot of personal experience being given here, do not run a gap that�s too wide, even .040� is plenty of gap.

[blueguy91]

103's gapped @ .050".

Don't over think it.

If that isn't working then you have another issue.