[gkopeck]

there's a lot of info on plugs here, but my question is...I'm using R45's in a 70 Chevelle that orginially had a 307. We have a '64 283 replacement in there, no more info on buildup. The guy sold me the R45's and said they burn a little hotter.
I'm having backfiring problems, with time set (i hope) correctly). Suggestions for a plug replacement?
thanks.

 

[JWagner]

The best info on your plugs is gotten by removing and looking at your plugs. If they are a light chocolate brown, they are OK. If they look dirty black and oily, like mine then it is time to go a step hotter. It may not be that easy to do these days as some of the unleaded gasolines do not leave a lot on the plugs. I would say that if your plugs are not black and engine does not ping or run on it is probably close enough. The 45's are a good choice.

 

[gkopeck]

what does the "s" stand for in R45S?
thanks

 

[gkopeck]

alright never mind the S, i've figured that one out at www.acdelco.com, but is there an appreciable difference in heat from a 43 to a 45? The charts say use 43 but i'm running 45's.