I am going to replace the old spark plugs in my 440, (stock engine) the parts house looked up my application and gave me champion RJ12YC, the ones that were in it were RJ18YC, is there that much of a difference between the two, it is my understanding that with champion plugs the higher the number the "hotter" the plug, should i go ahead with the colder one?

I think they gave you the right plugs, 18 is a awfully hot plug.

leave the champion plugs for your lawn mower. Autolite number 85

autolites are for fords RJ12YC is it man!!

NGK's work great in mine.

Another vote for Autolite 85's
I've used the Champions too with no problems, But stay away from Bosch Platnium in this application

If I have a choice I won't but jap crap in mine!
One summer my machinist talked me into trying other brands. It took him years as I was champs or nothing!! Being a ford guy he was big on autolites.
so we tried autolites first they were OK ran same times. then NKG they were OK ran same times but if you cold fouled them they stayed fouled. Then we got AC's they were OK ran same times but same as NKG on the fouling. we tried Accel they were OK ran same times and same as the preceding two if you fouled them they needed to be manually cleaned. Then we tried bosch platnuim they worked good but no better than a Champion so not worth the cost most of these plugs were given to us as people heard we were doing testing and were sure what they were using were the best. Car ran 12.0's nibbling on some high elevens at the time and was street driven. all plugs got at least two weeks of street driving and strip runs as we were racing every week end.
Now my machinist tells people the story saying in the end Barry was right overall the champions work best. That's probably the only thing we don't argue about and I never hear of it any more!!
Mopar says use Champion, Indy says use Champion and Edelbrock says use Champion and these guys should have an idea what works best with their products!!!!
This week end I had my plugs way cold fouled from hours of garage idling chasing and oil leak. they were cleaned up before the first burn out was done and ran flawless all day sunday!!!!!
C59CX if I had iron heads they would be RJ12YC's

PS I tell the chevy boys to stick with AC's and Ford boys to stick with Autolites and I just don't talk to the Jap scrap types!

champions are made in mexico and autolites in china

Most plugs are not very good. We raced a 13:1 max wedge car. Before we put any plug in it, we checked them with an old champion plug tester. AC, Autolite, Champion, and Prestolite all tested about the same. From 75 PSI to 130 PSI. We used only the ones that checked 120 or above. The car ran about .3 seconds faster with checked plugs. Later i ran a blown alc 517 hemi. Used 60 series (race) Champion plugs. Did not need to check them.

The 517 hemi we raced was in a monster truck (Dodge of course). Had be running it for a while and got feeling guilty about not changing the plugs so got a set of standard duty plugs. Changed them between rounds at a race in New York. It started and idled fine, but when i hit the throttle on the starting like the engine went to about 3000 RPM and then sounded like it hit a rev limiter. Went back to the pits, put the Champions (60 series) back in and it ran fine. Went from the Champions to NGK's and they worked just like the Champion race plugs. If you don't use race or tested plugs, good luck.

Very cool truck!!!

I have used Champs for years instreet cars and trucks, but I realize they may have changed in the last few years.

Now in my TAD 451" PSI blown hemi, it will consume 8 NGK plugs per 1/4 mile. It used to be 16 per run. I wouldn't think of putting anything else in there.

I had champs in my motors when i was a kid. They never lasted more then a few hundred miles. My 12.5 to 1 motor used to burn the electrodes right off them within a 100 miles. I've been using 85 autolites for over 30 years never had a problem. My local speed shop has been using them in his 440 powered 63 Dart for 35 years. Car runs 10.0 like clock work. I'll stick with whats been working for me for many years. And skip the Mexico and jap crap. This is America, the only thing we make here is bad politicians.

Had the correcdt heat range. Champion plugs suck in plain english. And don't kid your self them junk champion's aren't made in the US either. And if you hate parts made out side the US so much you better get rid of your Mopar. 99% of all the aftermarket and even name brand stuff is not made here. Even MSD is made outside the US.

Any Champion plug that makes it into my garage gets the hammer.
Many years ago I've wasted almost an entire year trying to get a 361 BB to idle or let alone started after I had put in a set of correct range Champion-plugs.
In that year I replaced almost everything on top end on that engine. Never could get to start and stay running properly. Then one day, out of the blue, I just put in the original set of used plugs consisting of 3 different brands which I still had kept, the motor fired up on the first turn.
Tried the Champions again, to no avail. Even bought another set thinking they might be defective by now from all the starting and such, they didn't work either.
From then on I hate Champion sparkplugs.

A local garage provides me with Accel-plugs.
"Accel 134" for bigblock Mopar motors. Got them in all my cars and never had one fail since years now.
I put them in and forget about them. With some of my cars I can't even remember when I did put the plugs in anymore, they seem to last forever.