Best Plugs for high Altitude?
 

Colorado to be specific.. 5280 ft.

Running Porken's S300 Chips with 87 FPR, xpipe, highflow cats and 2.25"
exhaust.

Just failed emissions miserably, hopefully that is because of a leaking
fuel damper though. I'm replacing that, plugs, filters and oil.

thoughts on best plug for this altitude?

What was your emissions numbers?

here's the data

Do you have the final numbers?

Try 1 range colder than the factory, but Usually it would not be the plugs. (that would be the last thing I would check).
Plugs are not something that are as directly influenced by altitude. Mixture is more influenced by atmospheric pressure but not plugs. Changing to colder plugs could mask a lean condition, or timing advanced too far condition.

Fix your fuel dampner you may have low fuel pressure leading to lean mixture leading to high NOx (nitric oxide) or O2. Usually u will not fail High O2 unless its for dilution, so I would

1: Replace with factory recommended heat range.
2: Make sure all the emissions vacuum lines are connected and not leaky
3: Replace that fuel dampner
4: Change Oil/Filters
5: Drive the car for about 20 minutes before going through inspection (get it good and hot)..

A leaking damper will dump raw fuel into the intake, so that's likely the problem. :eek:

Within reason, run the coldest plug you can, that doesn't foul. I recommend WR5DC gapped to 0.032"/0.8mm, but you could just as well run a 6 or the stock 7.