Gaskets and Freeze Plugs
Pontiac V8 Gaskets and Freeze Plugs
Small Parts, Big Consequences — Gaskets and Freeze Plugs for Pontiac V8s
Gaskets and freeze plugs are the cheapest parts on a Pontiac V8 and the ones that end a weekend. A head gasket sets deck clearance and adds volume to the chamber, an intake gasket has to match the port you actually have, and a rusted core plug or a missing oil galley plug will empty a fresh engine in a driveway.
Butler stocks Cometic MLS and Butler Spec head gaskets, SCE Pro and Titan copper, Best Gasket overhaul sets, four families of intake gaskets, D-port and round port exhaust gaskets, BOP Viton rear main seals and complete brass block and head plug kits.
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1. Head Gaskets: Composite, MLS or Copper
Three families, three different jobs. Pick by what the engine is, not by what is cheapest on the shelf.
| Composite | The stock rebuild answer. Best Gasket and SPM composite head gaskets cover the 326 through 455 family, including a universal Butler Performance gasket that fits all 1964 and later 326-455 engines and a 4.380" version for aftermarket blocks. |
| Multi-layer steel | Cometic MLS in Butler Spec sizes is what most performance builds get. Load-controlled embossments spread clamp load so you seal with less bore distortion, and the stainless outer layers carry an FKM coating with a PTFE topcoat for cold sealing and fret resistance. |
| Copper | SCE Pro solid copper needs o-rings and sealant; SCE Titan has the coolant and combustion seals built in and does not require o-rings in the block or head. Butler is direct about this one: copper is recommended for very specific drag race applications only. |
2. Picking Bore Size and Thickness
This is where most head gasket orders go wrong. The gasket bore should be roughly .010" larger than the cylinder bore, and thickness is a compression decision, not a packaging decision.
| Match the bore to the block | The Cometic 4.225" Butler Spec gasket covers 400, 428 and 455 blocks with bores from 4.120" to 4.211". Other stocked sizes are 3.825" for the 326, 4.100" for the 350, 4.200" for 389, 421 and early 1967 400 blocks, and 4.380" round bore for aftermarket blocks. |
| Thickness moves compression | On the 4.225" chamfered gasket, .040" adds 9.5cc, .051" adds 12cc, .060" adds 14.1cc, .075" adds 17.5cc, .098" adds 23cc and .120" adds 28cc. The .040" is the standard and most common thickness. Run those numbers before you order pistons, not after. |
| Round, chamfered or offset | Cometic builds custom MLS gaskets from .027" to .120" in round, chamfered and offset chamfered bores, with or without water holes. |
| No water holes | The no-water-hole versions exist for restricted-cooling race combinations. If you do not know you need them, you do not need them. |
3. Intake Gaskets Follow the Head, Not the Year
Butler splits intake gaskets into four groups because a Pontiac intake gasket that is wrong for the port hangs into the runner and costs flow, or leaks at the china wall.
| Cast iron, early style 1957-64, non Super Duty. | |
| Cast iron, later style 1965-79, | excluding Ram Air IV and Super Duty 455. |
| Cast iron Ram Air IV, large port, and Edelbrock out of the box (unported). | Out-of-box Edelbrock heads share this group with the factory large port castings. |
| Edelbrock ported, aftermarket and Ram Air V. | Once a head is ported the stock gasket no longer covers the opening, and Ram Air V ports are their own dimension entirely. |
4. Exhaust and Header Gaskets: Shape and Clearance
Two variables here, port shape and what the gasket has to clear on the way by.
| D-port | Butler's steel reinforced large port D-port gasket measures 2.120" x 1.540" and is designed to clear the dipstick tube. It covers factory cast iron D-port manifolds, Ram Air Restorations manifolds, and Doug's, Hedman, Hooker Competition and Flowtech D-port headers. Butler also carries stock D-port gaskets with relief bends for factory manifolds. |
| Round port | Sizes vary by brand, so measure before ordering. Butler stocks Mr Gasket at 1.880", SCE Pro Copper at 1.785", Hooker steel reinforced at 2.100", and an SPM Ram Air IV and Super Duty gasket at 1.920" sized for Edelbrock round port heads. |
| Copper and reusable | Mr Gasket CopperSEAL uses dead soft .043" copper with a .051" embossment around each port; Seal-4-Good multi-layer dead soft aluminum gaskets can be reused and port matched. |
5. Rear Main Seals
Pick by main journal size first: 3.00" mains cover 326, 350, 389 and 400 along with the 1979-81 265/301, and 3.25" mains cover 421, 428 and 455.
| Rope | Best Gasket braided Teflon and graphite rope seals, for a correct-appearing factory rebuild. |
| Two-piece Viton | BOP and SCE AccuSeal Pro single lip Viton seals, the straightforward upgrade over a rope seal. |
| One-piece dual lip Viton | The BOP one-piece relocates the parting line to reduce leak risk, uses a more pliable construction that tolerates seal groove geometry problems, and runs a double lip that also helps hold vacuum. |
6. Freeze Plugs, Block Plugs and the One Behind the Distributor
Do them all while the block is bare. Nobody enjoys pulling an engine to change a core plug.
| Block kits | Melling's brass block kit covers the eight 1 61/64 brass side plugs plus the 2 1/16 cam plug, the 15/16 rear plug, two 9/16 press-in galley plugs and two 3/8 pipe plugs. Butler's Ultimate Block Plug Kit adds the plugs most kits leave out and includes the install tool. |
| Cylinder head plugs | Butler's brass freeze plug kit fits 1965 and later Pontiac cast iron heads, offered with or without the press-in heater hose fitting for the rear of the passenger head. |
| The drilled galley plug | The 3/8" passenger side rear oil galley plug is drilled with a .040" hole to oil the distributor. Fit the undrilled version there and you have created a problem. Butler sells both, plus the pipe plug tool for installing it behind the distributor. |
| Aftermarket blocks | IAII and Butler aluminum blocks use o-ringed screw-in aluminum plugs and a 1" flush fit pipe plug at the rear, not press-in cups. |
7. Overhaul Sets, Valley Pans and Sealers
The last mile of a rebuild, and one real trap.
| Full sets | Best Gasket covers 1961-79 326 through 455 except Ram Air and Super Duty, offered with the rope rear main seal or without a rear main seal so you can run a Viton seal instead. There is a separate set for 1958-60 370 and 389 engines. |
| Butler custom overhaul set | Build your own kit from the same gaskets Butler uses in its engines, valley pan through oil pump, instead of paying for a box of gaskets you throw away. |
| Valley pan hardware | The install kits are not interchangeable. The kit for the Tomahawk TP-041S valley pan does not fit the N178WD, and the pre-1968 and N178WD kit does not fit the TP-041S. |
| Grommets and sealers | PCV grommets for valley pans and valve covers, the 1973-74 SD455 PCV block-off grommet, heater nipple caps, and Permatex sealers. |
Order the head gasket the same day you order pistons, and order the plugs before the block goes to the machine shop. If you tell Butler the bore, the stroke, the chamber volume and the deck height you are working with, they will size the head gasket to the compression you are after instead of leaving you to guess.
Freeze Plugs & Block Acc. Rear Main Seals Individual Gaskets Valve Cover Gaskets Intake Manifold Gaskets Exhaust Header Gaskets Overhaul Gasket Set Oil Pan Gaskets
Not sure what your Pontiac needs?
Email our tech team at tech@butlerperformance.com. Tell us your engine, heads, car, and power goal, and we will put the parts together as one combination that works.