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Multi-Layer Head Gaskets
Pontiac V8 Multi-Layer Head Gaskets
Clamp It Down — Multi-Layer Head Gaskets for Pontiac V8s
Multi-layer steel (MLS) head gaskets are what Butler reaches for when a Pontiac build is past the point where a composite gasket is the right answer — high compression, a power adder, or an aftermarket block. MLS gaskets use load-controlled embossments that spread clamp load, so they seal with less bolt load and put less distortion into the bores.
Butler stocks Cometic MLS gaskets cut to Butler Spec water holes in the bores Pontiac builders actually use, from 326 pocket bore through 4.380" round bore for aftermarket blocks, in thicknesses from .027" to .120", plus build-your-own gaskets with or without water holes.
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1. What an MLS gasket actually does differently
A multi-layer steel gasket is not just a stronger composite gasket. It works on a different principle.
| Load-controlled embossments | the layers carry embossed beads that conform load distribution across the sealing area. That creates an exceptional seal while requiring less clamp load, which in turn means less bore distortion — the thing that costs you ring seal on a high-output engine. |
| Coatings | the stainless steel outer layers are coated with FKM (Viton), a high temperature and chemical resistant polymer, with a PTFE topcoat that resists fretting and improves cold sealing. |
| Surface finish matters | MLS gaskets want a good, flat, properly finished deck and head. If your machine work is not there yet, that is the conversation to have before ordering. |
2. Pick the bore size first
Gasket bore is chosen off your finished cylinder bore, and Butler stocks the sizes that cover the Pontiac range.
| 3.825" pocket bore | the 326, chamfered, in .040" and .051", cut to Butler Spec water holes. |
| 4.100" chamfered bore | the Pontiac 350, in .040" and .051". |
| 4.200" pocket bore | 389 and 421, and the early 1967 400 that carries 389-style chamfers in the block. Stocked chamfered in .040", .051" and .060". |
| 4.225" chamfered bore | the volume seller. Butler's product data notes these are commonly used in 400, 428 and 455 engines with bores of 4.120" to 4.211", and they fit both round bore and chamfered bore blocks. |
| 4.380" round bore | for aftermarket blocks, in .040", .051" and .060", plus a five-layer version in .044" for the highest-output combinations. |
3. Then pick the thickness, because it changes compression
Thickness is a compression tuning tool on an MLS gasket, and Butler's product data gives the gasket volume so the math is not guesswork.
| .040" is the baseline | Butler lists .040" as the standard and most common thickness. On the 4.225" chamfered gasket that is a gasket volume of +9.5cc. |
| Going thicker drops compression | in the 4.225" family the volumes run +12cc at .051", +14cc at .060", +17.5cc at .075", +23cc at .098" and +28cc at .120". That is how you dial a build back onto pump gas without cutting pistons. |
| Going thinner raises it | the 4.225" gasket is also stocked in .036" and .027" for squeezing quench and compression out of a combination that needs it. |
| Quench, not just ratio | gasket thickness sets your piston-to-head clearance as much as your compression ratio. Decide both at once, with your piston deck height in hand. |
4. Bore type, water holes and build-your-own
The last two choices catch people out, so make them deliberately.
| Round, chamfered standard, or chamfered offset | the bore treatment has to match what is in your block. Butler's stocking 4.225" gaskets fit both round bore and chamfered bore blocks; the smaller-bore gaskets are cut specifically as pocket bore or chamfered. |
| Butler Spec water holes | the stocked Cometic gaskets are cut to Butler's own water hole specification rather than the generic pattern. |
| No water holes | a no-water-hole version of the build-your-own gasket is available for block-filled and restricted-coolant race engines. |
| Build your own | Cometic gaskets can be ordered from .027" to .120" thick in many bore sizes, round or chamfered, when nothing on the shelf matches your combination. |
If you are putting a stock-bore 400 back together for street duty, a composite Butler head gasket is usually the right call. MLS earns its keep the moment cylinder pressure goes up — boost, nitrous, high compression, or an aftermarket block. If you are unsure which side of that line you are on, call with your bore, deck height and combination and Butler will put you on the right gasket.
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.