Hey Everyone - I was helping a buddy from my Olds club look at options for a new project. In helping him, I keep seeing references about how 1978 was somehow "special" in terms of the mounting points or engine position and that non-78 engines will not fit. Is this for real? Or is this another urban legend like the Cutlass Supreme supposedly "needing" different engines than all other Cutlasses?

Here's the most recent thing I saw that made me write this question (but I've read this elsewhere, too):
https://www.ebay.com/itm/5-7L-V8-Eng...ESTx:rk:8:pf:0

 

In 1978 some Cutlass models came with Olds engines and some came with Chev engines. It's not a myth. My 78 Cutlass Calais had a Chev 305 4bbl. AFAIK, none of the Cutlass models came with a 350 though.

 

OH, that must be one of the rare "offset" Supreme motors...

Hint: that ebay seller is an idiot.

Once again, EVERY SINGLE Olds V8 from 1964-1990 has EXACTLY THE SAME motor mount locations on the sides of the block. I suspect where this probably came from is that the 78 in question was originally a diesel car. The Olds diesel used an adapter plate to move the driver side motor mount forward to accommodate the oversize diesel starter. The block still has the same tapped motor mount holes as does every other Olds block, but a steel plate was bolted to them to move the mount forward. The frame pad is relocated on the crossmember to match. If a clueless person tried to install a gasoline engine in a 78-85 diesel car without putting the frame mount back into the gas engine location, they would likely come to this erroneous conclusion.

 

Note how the driver side frame mount (right side in the photo) is offset from the passenger mount in this photo of a diesel car. Also note that the holes to relocate that mount rearward to the gas engine location are already drilled in the crossmember - you can see the top one just behind the driver side mount.

 

Allen, Joe - Thanks so much for the clarifications! The pictures and details really help out. I think you are right, the ebay guy isn't sure what he's got, but he's trying to avoid complaints after the sale. Yeah, the rare offset Supreme engine myth even throws off RockAuto and other good vendors

So brings up one other question...
If you've got a 1978 that originally came with an LD5, Buick 231 or the LG3/4 Chevy 305's, it'll have Chevy SB mounts, right? Does that mean you'd need "Chevy to Olds swap" mounts to get an older model Olds 350 to bolt in? Or would it be better remove the original mounts and just weld in correct SBO mounts?

 

The SBO was a factory option in these cars. Simply get a set of the SBO frame pads and bolt them in. The crossmember is already drilled for them. Any 78-88 A/G-body or 77-90 RWD B/C-body that came with an Olds motor is a donor. Note that unlike the older cars, these frame mounts are different RH/LH (note the location of the upper bolt). I'll also point out that these frame pads use the 2328 style rubber motor mounts with ANY Olds V8.

 

Joe can verify, but I believe the Chevy engine mounts will be different than Olds.
Motor mount application list

 

Of course they are, which is why I said to obtain and bolt in a set of SBO mounts for a G-body. The V6 mounts are also different. The 260 mounts, on the other hand, are exactly correct. And if you go to the ebay ad that the OP linked in his first post, it is clearly an OLDS motor that the seller is claiming won't fit a 78. The fact remains that the diesel mounts are positioned asymmetrically, as shown in the photo I posted.

 

This is exactly what I was wondering. Great to find out that they pre-drilled for the Olds mounts, even in cars that got the Chevy and Buick engines. Thanks again for the info!

 

The frames are exactly the same no matter which engine got installed at the factory. Also, the Olds and Chevy motors were the only V8s that were used throughout the entire production run of the 78-88 cars, so the frames for each year had to maintain that compatibility.