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Engine Adaptors
Pontiac V8 Engine Adaptors
Crossing Generations — Engine Adaptors for Pontiac V8s
Pontiac changed the engine mount bolt pattern on the block partway through the V8's run, and engine adaptors are how you bridge that gap. A 1969-and-earlier block has only two engine mount holes; later blocks do not match it. Put an early engine in a later car, or a late engine in an early car, and the adaptor plate is the part that makes the factory mounts work.
Butler builds the MM5 and MM6 adaptor kits for crossing those generations, the F10774 engine mount adaptor for putting a 1961-1979 326-455 in a 75-81 F-body, and stocks Warpath Restoration adapter kits.
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1. Which Way Are You Going
All three Butler kits solve the same class of problem, but they run in different directions. Pick by what is going into what.
| Early engine into a later car | the Butler MM6 kit installs a 1969-or-older Pontiac engine, meaning a pre-1969 block with only two engine mount holes, into a 1970-and-up chassis. You keep the original chassis-specific frame and motor mounts and the plates make up the difference. |
| Late engine into an early car | the Butler MM5 kit does the reverse, putting a 1976-and-up engine into a 1969-and-earlier chassis. Butler notes it also adapts a 76-and-up engine into a 1970 LeMans. |
| Any 61-79 engine into a 75-81 F-body | the Butler F10774 engine mount adaptor is built for 1961-1979 326-455 engines going into a 1975-81 Firebird or Trans Am. It replaces the factory engine mount on that car, and its extra bolt holes adapt a 61-69 two-bolt block for use in a 70-81 F-body. Butler notes the 403 is excluded. |
| Warpath Restoration | an adapter kit that takes a 1965-69 two-bolt block into a 1975-81 F-body, available with a rubber frame mount. Butler notes it may interfere with some headers, and some 389 and 428 blocks may have to be clearanced. |
2. What Comes in the Box and What You Still Have to Do
| MM5 and MM6 hardware | each kit includes two adaptor plates, four 7/16"-14 x 3/4" grade 5 bolts, four 7/16" lock washers and four 7/16" flat head bolts. You supply nothing but time. |
| The late block boss | this is the gotcha worth reading twice. Butler notes that some late 1970s Pontiac blocks have a boss that interferes with the adaptor plate. If yours does, the boss has to be ground for clearance, or that side can be drilled and tapped to 7/16" so the mount bolts directly to the block. If you drill and tap it, that side does not need an adaptor plate at all. |
| The plates must sit flat | Butler states it plainly. An adaptor plate that is riding on a boss or a burr is not clamped, and a mount that is not clamped will work itself loose. |
| Alignment is normal work | all of these kits carry the same note, that they may require some modification or slight shifting of the frame mounts to get proper alignment. That comes both from the thickness of the adapter itself and from tweaks in a fifty-year-old frame from use and damage. Hang the engine, check it, then tighten. |
3. What Else to Order With It
| Mounts, separately | MM5 and MM6 are plates, not mounts. You still use the correct chassis-specific frame and motor mounts for the car, which live in the year-specific subcategories. |
| Poly mount clearance | if the car is getting Butler polyurethane engine mounts, Butler notes that when using them with the MM5 or MM6 adapter plates some modification may be necessary to let the adapter bolt sit flush with the mount. |
| Frame mount spacers | if the swap leaves the pan close to the crossmember, the chassis-specific frame mount spacers are the correction, not a taller mount. |
Identify the block's mount hole count and the chassis year first, since those two facts pick the kit. Order the chassis mounts at the same time so the whole stack-up gets trial fit in one session rather than three.
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.