Here is what i just posted the other day when the same exact question was asked of 215 heads.
Scott
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Try the R44XLS 1st with those heads as they are the stock replacement AC plug for the 396/325 & 350hp motors ,you can tweak the heat rang up/dn as required from there. The hotter 396/375 hp used the r43xls plugs.
The original plugs in mid 60's-68 & for 69 were either 44n to 1968 & then r44n (r=resistor) from 69 & up. in std tip design. But the xl or xls series are the extended tips plugs that were a later issue plug specifically designed to run cleaner with the tip extended a little further into the combustoin chamber which did help out.
When running the later extended tip design XL/XLS plugs if the motor was idling or at low/low load rpm the plugs would run a little hotter staying a little cleaner but when under a load with a lot of throttle or at WOT there was more airflow and fuel passing by the extended tip of the pulg actually cooling it a bit,it was a good design upgrade at the time for sure.
All these are the longer each plugs which those 1967-68 215 heads should be running.
NOTE:you can also have these AC Delco plug #'s corss ref'd to a plug brand of your choice.
Scott
Scott
=========================================
Try the R44XLS 1st with those heads as they are the stock replacement AC plug for the 396/325 & 350hp motors ,you can tweak the heat rang up/dn as required from there. The hotter 396/375 hp used the r43xls plugs.
The original plugs in mid 60's-68 & for 69 were either 44n to 1968 & then r44n (r=resistor) from 69 & up. in std tip design. But the xl or xls series are the extended tips plugs that were a later issue plug specifically designed to run cleaner with the tip extended a little further into the combustoin chamber which did help out.
When running the later extended tip design XL/XLS plugs if the motor was idling or at low/low load rpm the plugs would run a little hotter staying a little cleaner but when under a load with a lot of throttle or at WOT there was more airflow and fuel passing by the extended tip of the pulg actually cooling it a bit,it was a good design upgrade at the time for sure.
All these are the longer each plugs which those 1967-68 215 heads should be running.
NOTE:you can also have these AC Delco plug #'s corss ref'd to a plug brand of your choice.
Scott
