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Plugs for 72' and Later Cast Iron Heads
Pontiac V8 Plugs for 72' and Later Cast Iron Heads
Taper Seat — Plugs for 72' and Later Cast Iron Heads for Pontiac V8s
From 1972 Pontiac cast iron heads went to a 14mm taper seat plug with a 5/8" hex and a .460" reach. There is no gasket on these: the plug seals on the cone, so an early gasket seat plug is the wrong part even though it threads in.
Butler stocks the NGK R5673 and R5674 series for these heads along with the UR5 and the resistor-type YR-5, in recessed tip and extended tip and across a wide spread of heat ranges, in sets of eight.
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1. The 1972 Change
This is the single most common spark plug mistake on a Pontiac, because both plugs are 14mm and both will start into the hole.
| Taper seat, no washer | These plugs seal on a machined cone in the head. There is no crush washer to lose and none to add. |
| 5/8" hex | Smaller than the 13/16" hex used on the earlier iron heads, so you will want the thin wall plug socket. |
| .460" reach | Shorter than the 3/4" reach used in Edelbrock aluminum heads. This group sits between the other two families on every dimension that matters. |
2. Tip Style
Butler stocks both tip styles for these heads, which is a real choice rather than a preference.
| Extended tip | The R5674 series and the UR5 put the electrode further into the chamber. This is the common street setup. |
| Recessed tip | The R5673 series and the YR-5 pull the electrode back, which is the safer answer where clearance is tight or cylinder pressure is high. |
| Resistor type | The YR-5 is a resistor plug, which is what to run when the car has electronics you would rather keep ignition noise out of. |
3. Heat Range
This group spans a wider range than the early iron heads, from 5 at the warm end to 9 at the cold end.
| Heat range 5 | The warmest parts here, the UR5 and the YR-5, and the ones suited to a mild street engine that idles a lot. |
| Heat ranges 6 through 8 | The working middle of the range for a street and strip Pontiac, available in both tip styles. |
| Heat range 9 | The coldest plug in the group, listed for nitrous. It will foul in a street engine. |
Confirm the seat in the head before ordering rather than going by the year of the car. Heads get swapped, and the casting in front of you is what decides this.
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.