Spark plugs

[DenaliWhip]

This informative thread, has answered my question on spark plugs and I just wanted to say thanks to you guys. I just purchased 04 Denali, am stock w/ no mods and wanted to tune it up its at 109k.

Looks like im going with stock replacements Ac Delco.

 

[withac]

Im running NGK. 55's I think. Several people on here have em. Works great and if you make the gap .04 even better!

I'm running NGK Power Plats, it's been a while since I installed them, are they the same as the TR55, that sounds real familiar. I changed them at around 90K and replaced the wires too, saw an immediate increase in mpg.

 

[TqMnster]

ACDelcos gapped to .04 and new wires got my truck running like a top again. Picked up all my missing gas mileage at 145k miles. The plugs the previous owner had it in were NGKs gapped to .065 and the .04 runs soooo much better!

 

[withac]

ACDelcos gapped to .04 and new wires got my truck running like a top again. Picked up all my missing gas mileage at 145k miles. The plugs the previous owner had it in were NGKs gapped to .065 and the .04 runs soooo much better!

The NGK's (the NGK site refereces a G-Power TR5GP but I'm sure it was a 55) I put in were pre gapped and in fact NGK said not to try and gap them as you could damage the very small center electrode. They came gapped at .04

 

[TqMnster]

I didnt look too hard for a number but I did check the gap and they were all .065 and werent in the best of shape. I've always had good luck with NGK plugs. Just went back with acdelcos (pregapped to .065) and gapped to the recommended .04 and it runs noticably smoother!

As far as gapping the ngks the electrode does come to point which I could see being pretty vulnerable. I would gap them down but do it very slowly to keep from going too far. I would not try to spread it any though...

Edit: Theres no telling how long those plugs have been in there so I'm sure NGK started pre gapping to spec for the specific application to avoid people breaking the electrode trying to do it their self. I'm sure these were older plugs, they sure looked to be...

 

[Zed 71]

Yep OEM or NGKs. Do not use Pulsars (or whatever they are called), E3s, or plugs with 4 tips (I think Bosh 4+s).