View Full Version : 1978 425 engine

09-11-11, 08:07 AM
is most of the 425 engine interchangeable with the 472 and 500?

09-11-11, 12:04 PM
Take a look down in Discussions, Item Specific: Engines. This Deville Forum begins at the 1985 model year.

09-20-11, 09:04 PM
The 425-472-500 motors are the same on the outside and are bolt ins... so if you want to pull out your 425 and put in a bigger motor , no problem.. Even if you had a 368 any of those motors will bolt in, but the 368 exhaust is too small for the bigger motors..

09-21-11, 04:35 AM
Isn't there an issue with oil pan clearance when putting a 500 in place of a 425?

I've been preparing to do the swap on my 78 Sedan DeVille, and from what I understand; I'd have to use the 425 oil pan.

Other than that, I don't think you would have an issue.

09-21-11, 10:48 PM
When putting a 425 or 368 oil pan on a 500 , because of the longer stroke, the rods come very close to the bottom of the pan... sometimes they can touch the bottom... what has to be done is hammer and dimple the bottom in a few spots where the rod bolts get close to the bottom of the pan...

09-22-11, 09:21 PM
And don't forget the 425 right exhaust manifold.

09-25-11, 01:19 PM
The right side 425 exhaust manifold will bolt up and work without a problem.. but the 425 manifold has a indent to clear the "A" frame bolt.. this indent cuts down on the flow and may cause a loss in a horsepower or two... Many guys like to use the 472-500 manifold an do a few little mods to make it work...

The Ape Man
09-29-11, 09:25 PM
When putting a 500 in place of a 425 in a rear wheel drive car change the oil pan and oil pickup to the ones from the 425. They fit fine. One main cap bolt needs to be moved for the oil pickup tube bracket.

The oil pump housing must be swapped too.

The 500 manifolds work on both sides if you saw the extra length off the upper A arm bolt. Worthwhile because of flow verses the 425 stuff.