I figured it's past time to change out my spark plugs that were installed back in '08. Saw some wear on one plug from the passenger bank, some brown deposits building up on passenger bank plugs too.

Old plugs that were installed by a shop in '08 were AC Delco 4355, and I was able to get some Champion RJ12YCs off EBay a while back.

Just finished installing them (1 hour just to get the rear-most plug on the driver's side , 2 hours to get them all done using hand tools..I don't miss wrenching for a living at ALL )

Anyhoo, think these plugs might be a tad too cool for surface street driving?

I'm going to break them in traveling out to a prison 75 miles away that I go to for leading a Bible study tonight, but I figured I'd ask those more knowledgeable on this fine board their opinions...I hope it doesn't break down into this

What say y'all?

I think that you will be fine. Especially if you do some hiway driving.

Lot's of production cars run colder plugs I don't think its an issue.

You will be fine. A Champion rep told me the new then (20 years ago or more) RJ12YC plug was designed to cover multi ranges from 10 to 13 or was it 11 to 14?? always worked great for me as did RN12YC in my small blocks.

RJ12Y is actually hotter than J11Y. The racers would run a colder plug like an J10Y. I think an RJ12YC will work better with today's gas and a stock ignition system but probably not ideal if you have a hot ignition system like MSD?

Thanks for the opinions/advice, gentlemints, the car sure seemed a lot "happier" tonight

i used them for decades on all my stock vehicles.

RJ12YC is the stock spark plug replacement ( being 11s are not anymore available ). Being a stock replacement, is the correct piece for a driver on a stock engine, even for slightly "tweaked" engine

That was the point the rep was making the 12 series plugs were redesigned in the late 80's to cover more ranges to make a nice street or street strip plug. I ran 11.13s the last year with iron heads and had run them street strip for 10 years with a 6AL. I would change them out once a season just because at $2 a plug why not.

One year we tried autolite, AC, accel, NKG and Bosch platinum none made improvements the Bosch looked like it had a better street life drove the car on the street till December that year and used them first time out in the spring but they were $6.50 a piece plugs.
all plugs ended up being supplied by other racers/freinds when they heard we were doing plug test as they were convinced their plugs were better save for the autolite they were provided by my machinist and pit crew as he spent years to get me to try something else and the bosch we supplied buy a lawnmower shop in the same complex we rented a shop he was a big bosch man and got them special from the rep.

So from early april till early dec all we changed on the car was plugs and oil racing most week ends and driving back and forth to work most weeks!

12s will be fine, I run 9s in my street car, but I have a hotter ignition. Any hotter and you would probably suffer from pre ignition. They are an extended tip plug that should clean up nicely one on an extended trip. Perfect for daily driver.