I have a '65 Riviera with 62,000 miles. I see where AC has discontinued the 44S and R44S sparrk plugs. The 43 heat range can cause fouling from what I read, and the 45 can cause pinging. Anybody know of an acceptable R44S crossover? The car is all stock,and I prefer to keep the standard heat range if at all possible.
I'm running 43s in my 300 Skylark that originally called for 44s, and they aren't even close to fouling. You should be all right, but the Autolite 85 is often considered a direct crossover from the 44. Try this website... http://www.sparkplug-crossreference.com/
Be careful with interchange charts and heat ranges, they might not correlate with completely accuracy. I've approached this with caution after having a sudden pre-ignition event damage an engine. I've seen that the Autolites tend to run hotter than the GM equivalent. On the chart I just looked at Autolite 84 also exchanges. What I do with performance or motorhome apps. is to install the set you think you will use on one bank (the harder one to get at), and also on the rear cylinder of the other bank. The remaining 3 get test plugs, bought individually (I charge it to the job). Then I creep up on running it hard, gradually increasing load and time to get a read on them. Some engines just don't like some plugs.
This is what I used and they seemed to work well. Going back with these again on the fresh rebuild and going from there. I found the best price on them at O'Reilly I believe, but check Amazon as well. Sometimes they have good prices on the sets of plugs. NGK Stock# 3332. It is there XR5 plug. I put this in my stock 401 and like I said will be using them again on my rebuild which will be quite a bit beefier.
http://www.sparkplug-crossreference.com/convert/AC_DELCO/R44S http://www.summitracing.com/parts/ngk-3332
Finally decided to give the NGK XR5 a try. It crossed on O'Reill's website from AC 44S, so we'll see how it goes.
Plenty of info on the net regarding reading plugs for timing and heat range indications. Larry Meaux would be a good name to search for this.