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07-14-2016, 02:28 PM
Will a Oldsmobile 403 engine (1977 mod)fit in my 1968 Skylark without to much problems?

bob k. mando
07-14-2016, 04:02 PM
will it physically fit? sure, the 403 is a short deck Olds and the 68 Skylark could be gotten from the factory with a big block Buick 400. front to back space should likewise not be an issue as bore spacing on a BBB is 4.750" while the Olds has a slightly narrower pitch at 4.625"

will it bolt up to your transmission? yes, it has the BOPC pattern bell housing. however, the Olds mounts the starter driver side ( Buick mounts the starter passenger side ) so is unlikely to have the bell housing kick out where you need it unless you have a dual pattern bell on the trans.


another consideration is that most of the electrical on a Buick is backwards to the Olds. not only does Olds mount the starter on the 'wrong' side, Buick puts the distributor at the front of the engine while Olds mounts it next to the firewall.

another issue is that the 403 uses a "windowed block" architecture in order to keep the weight of the assembly down which makes the block weak. so if you intend to build this engine over 500 hp you may have some pretty serious issues keeping it together. this is why the 403 ( largest displacement and bore of any GM small block ) has never really caught on with hot rodders. they can be built for decent power ~ 400hp ( there is a Hot Rod magazine article ) pretty easily but if you try to go big, you're likely going to have serious issues.

the "simplest" non-Buick transplant would probably be a Cadillac engine, which shares much of the Buick design philosophy including bell pattern, starter placement, distributor placement and integrated aluminum front timing cover / oil pump. however, the 5.000" bore spacing could likely make it necessary to convert to electric fans on the radiator.

the Buick 455 would obviously be the most popular engine upgrade. it is a bit longer front to back than the small block Buick 350 ( 4.240" bore pitch ) but is not much taller than the 350 due to the Buick 350's huge stroke length. you'd need the 455 frame pads and engine mounts as well as the big block block fan shroud but there isn't much else to the swap.

08-03-2017, 10:28 PM
Speaking for the Caddy big blocks, if you can find one, a company named CAD500 offers full support. They're also light for thier size. A fully dressed 472 or 500 weighs just 40 pounds more than a fully dressed Chevy small block. Cadillac big block engines have been built to 1000 hp without modification to the bottom end. Obviously the heads, intake manifold and valve train would need upgrades. Big Block Caddys shine where torque is concerned. I have a 425 in my 64 LeSabre. It is stock, sans emissions and an Edelbrock carburetor. Hp is about 250 at 4000 rpm and 400 ft lbs of torque at 2000 rpm.