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Plugs for 71' and Earlier Cast Iron Heads
Pontiac V8 Plugs for 71' and Earlier Cast Iron Heads
Gasket Seat, Short Reach — Plugs for 71' and Earlier Cast Iron Heads for Pontiac V8s
Pontiac cast iron heads through 1971 use a 14mm gasket seat plug with a 13/16" hex and a 3/8" reach. That combination is specific to the early heads: the crush washer does the sealing, and the big hex is why these still come out with an old-style plug socket.
Butler stocks the NGK R5670 series for these heads in a spread of heat ranges with an extended tip, sold in sets of eight so a Pontiac V8 gets a matched set every time.
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More About Plugs for 71' and Earlier Cast Iron Heads
1. What These Heads Take
Three dimensions define this group, and all three differ from the 1972-and-later iron head plug.
| 13/16" hex | The larger of the two Pontiac plug hexes. The later iron heads went to a 5/8" hex. |
| 14mm gasket seat | The plug seals on a captive crush washer, not on a cone. A taper seat plug will not seal correctly in these heads. |
| 3/8" reach | Short. Edelbrock aluminum heads take a 3/4" reach plug, so those parts are not interchangeable either, even though both are gasket seat. |
2. Picking the Heat Range
Butler carries the NGK R5670 family in heat ranges 6, 7, 8 and 9, all with an extended tip.
| Heat range 6 and 7 | The warmer end of the group. These are the ones that suit a street driven Pontiac on pump gas. |
| Heat range 8 | A step colder, for engines making real cylinder pressure or seeing sustained wide open throttle. |
| Heat range 9 | The coldest of the group and the one listed for nitrous. Do not put it in a mild street engine, because a plug that is too cold will foul. |
3. Ordering and Installation Notes
A few practical points on this group.
| Sets of eight | These are sold as a set for a V8, which keeps the whole engine on one part number and one heat range. |
| Do not reuse a crushed washer | The gasket seat only seals properly once. That is part of the reason these plugs are treated as a consumable. |
| Wires | Butler's custom-routed Pontiac wire sets are built to reach these plugs with the wires run around the engine rather than over the valve covers, which keeps them off the headers. |
If you have already swapped to later iron heads or to Edelbrock aluminum, you are in the wrong group. Head castings, not the year on the title, decide the plug.
Not sure what your Pontiac needs?
Call our tech team at 866-762-7527. Tell us your engine, heads, car, and power goal, and we will put the parts together as one combination that works.