I'm 80% complete with a bottom up restoration of a 69 Camaro RS/SS 396 / 325 hp. Body is coming along very well but I'm at a stand still completing the engine. Working through a spark plug solution. Yes, there are R44N / R43N's available on ebay but I'd like to be able to get a more current spark plug. Plenty of input from other forums, spark plug cross reference charts, and the like BUT in many cases they don't all match up. If you have this dated engine then you know that the R44N (hot) /R43N (cold) are 13/16 with a 3/4" reach but threads only cover the lower half of the plug and the rest is slightly tapered with a gasket. I have not been able to find a half thread spark plug with a taper. Champion offers (and reflects in their cross reference chart) the 404 (RN12YC) and the 415 (RN9YC) that would offer me two heat ranges BUT they are both fully threaded. Autolite is doing the same thing with a 404 plug. AC Delco offers the R44XL and R43XL that appear to be exactly the same as the R44N's but they again are fully threaded. I've got some age to me and memory isn't what it use to be but weren't the full threaded plugs meant for the aluminum heads? So, if the taper on the R44N plug is not a huge factor then it kind of makes sense that the R44XL/R44XL/404/415 (that have full threads) would be a suitable replacement without damaging the heads. I'm convinced that someone has a solution that works well for them and would appreciate your input.

 

GM changed the spark plug design to a tapered seat in 1971 (no washer), the heads have a chamfered hole. If you have the correct vintage heads, you would be using the flat seat plugs with a crush washer.
AC Delco R44XL copper plug would be the one, no need for any fancy platinum etc. plugs. FYI, copper plugs dissipate heat better and faster than the other types, but they wear out faster.

 

Camaro 69. Thanks for your comments. Of the multiple sites and people I've talked to your explanation makes the most sense. Seems that there are no differences between the R-44N and R-44XL except the XL is full threaded, with a 3/4" reach 13/16 socket. If the heat range is the same then I'm good to go. Q: If these run cold, is there a hotter plug I could use?