Spark Plugs
 

Just wondering what type plugs to replace the stockers with and if anyone noticed an improvement in mileage?

It's my understanding from reading the forums that most people agree the Delco OEM plugs are as good or better than any replacement. They are most certainly the best bang for the buck (free).

if you have an 07 or later your plugs are iridiums. leave them on.
some really later 06s had them too.

I have an early 06' with over 107,000 miles and I've noticed mileage going down a little , about 24 MPG.I've used AC Delco Rapidfires in the past and have had great performance from them as far as a little increase in HP and mileage but have heard good things about the E3 plugs which are the main ones I'm curious about.Have any of you used them or know if they really live up to their claims? Otherwise I will go back to the Rapidfires if they make them for the Ecotec.

the new cars come with iridium and are good plugs.
i replaced the stock delcos w Iridiums and they have been great and worked well and i tend to have a sporty foot

I tried the e3's had a SLIGHT increase in milage but, it caused SERIOUS misfires I left them in for quite sometime, about 6-8 months, and gave the computer plenty of time to get to know the plugs. The engine just didnt like them though, put the stock ones back in and all is right with the world again.

Anyone know if they make a AC Delco Rapidfire for our HHR's ?

Any idea as to why the misfires were occuring with the E-3 's ?

bad plugs...maybe damaged when installed...try another set and see what happens

In GM I always used AC Delco plugs. I have an o6 LT with 130,000 on it. I use Delco Rapidfires #17 plugs. They work great. My HHR will do about 107 mph. The only other mode I have is an Air Hog air filter.