Spark plug BRISK or AC DELCO

AC Delco CR43TS.

Copper plugs are actually the best for performance, precious metals just last far longer.

The ER12S look better than the OEM units that came out on the first change, these have been in for a year.

I'd use the original equipment AC Delco plug. Rockauto has them for $6.31 each, with a $3 per plug rebate offered.

At least with double iridium ACDELCO on the c5. It’s 100k intervals.

I've ran these for a few years stage 2 e85, with absolutely no issue at all. The last year and a half I've been running a bigger turbo, powermax 2260 and have had zero issues

Been running them for the last year on EQT stg 1 91 and e30 with no issue.

What plugs you're using may help. In my experience not all plugs are created equal. Brisk, for example, last maybe 5-10k miles before they're garbage. Whereas I can run NGKs for 15k+.

Brisk silver er10s if you need 2 steps colder. I had the ngk plugs, but they wore down just as fast and are more expensive. Brisk silver are like 10 bucks

When I got my S60 (2006, T5) the previous owner had some copper AC Delco plugs made to fit an 850 non turbo in it and I wondered why there was very slow engine response.

ditch the delco plugs, they are trash. And delcos are shit plugs.