455 Swap

Q: 455 Swap

I have an opportunity to buy a 455 out of a bonneville. Anybody know what (if any) modifications I will need to do to get it to fit?

A: This is a very simple swap. Since 1967, all Pontiac V8s have the same external dimensions, and will readily swap parts like intake manifolds, timing chains, and oil pans. The exception is the much maligned 301.

As another list member mentioned, the Feb. 2001 issue of Car Craft has a brief article on swapping a 326 for a 455. It contains some good photos of the differences between the 1969 and earlier motor mount bosses/holes and the 1970 and later version. There is also a good description of water pump and pulley issues that need to be addressed. The article would apply to those of you with 350s and 400s as well.

But, essentially, the easiest way to do the swap is to take the timing cover, water pump, pulleys, and accessory brackets off your present engine, and transfer these to the 455. The same applies to your exhaust manifolds. Now the 455 will just bolt into place like it grew there.

Some other issues not mentioned, or only lightly covered in the article are:

-Flywheel/flex plate. While the majority of Pontiacs in the late 60s and early 70s used the same sized crank shaft flange, the late 50s and later 70s car are different. In fact, there are up to 5 different diameters in the Pontiac engine family. So, measure the rear flange on your 455 and check to make sure that your original flywheel/flex plate will bolt on, or use the one that came with the 455 if possible.

– Manifold sealing. Intake ports on Pontiac heads changed roughly about 1972, so if this engine is later than that, you’ll need to get the correct gaskets to seal your intake manifold. In the Car Craft article, they used some thin metal to block off the heat passage crossover, which is the area that will most likely leak. This is assuming you will be using a 1972 or earlier intake manifold.

– Engine weight. While we don’t have any exact figures on engine weights, it is logical to assume that a 455 weighs more than a 326, perhaps. You may have to get new front springs for your car if once the bigger engine is in and your front suspension bottoms out.

– Water pump/pulleys/ accessory brackets/timing covers. Pontiac in it’s infinite wisdom, changed the design of these front engine dress parts several times, and mixing these parts leads to poor pulley alignment, thrown belts, and premature baldness. But to give them credit, the blocks themselves are pretty universal.

Whatever you do, use all the parts from either the donor Bonneville, or your present engine.

The 1967 and 1968 Pontiacs (as well as the earlier engines) used an 8 bolt timing cover and pump. In 1969, they went to an 11 bolt cover and pump, but had two different pump designs, each a different height. This means that the pulleys and brackets are different for each pump type. The 1967 and 1968 items have different part numbers also, and they may be incompatible as well. But I don’t know for certain. That’s why you’ll stay sane longer if you source these parts from just one car.

– Engine mount bosses. The 1969 and earlier engine blocks were cast with two drilled and tapped bosses or holes for the engine mounts, along the oil pan mounting flange. In 1970, because many of the new cars had undergone chassis redesigns, the new blocks were cast with 5 bosses to allow the engines to be mounted in either earlier (pre 1969) or later chassis.

Some of the blocks cast in the ’70s don’t have all of these holes either drilled or tapped. Others do. If your 455 doesn’t, it shouldn’t be too hard a job to drill and tap the required holes. Use a correct engine bracket for a guide.

The other recourse is to use engine change brackets available from Year One, Performance Years, and AMES.

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