New here, not an expert by no means. Just thought I might share some info. With that being said, I worked at a used car lot in 90's. We bought an 86 or 87 Eldo (its been a while, so bear with me) that came with 4.1 or 4.5, maybe. Anyway, it was the smaller body style Eldo with a 4-T60 4sp trans. We bought the car from a GM tech that pulled the old motor bc it had bottom end knock, and he had replaced it with a 4.9 from a much newer model. When I read your post it reminded me of it from years ago bc the car was TBI and the motor that he replaced it with was a mutiport inj. So he used the throtle body that came with the car and just put frezze plugs in the holes that the injectors from the mutiport system used to be. The install looked clean and factory, and the car ran as it should have to best of my memory. Hope it helps.
Generally speaking,things really changed a bunch from 85' up. I sure there is a way to swap a whole subframe/driveline assembly but you certainly would be involved with countless modifications mostly electronic. The mechanical differences are the easy part.
Can't really remember what an 85' looks like. Think its the much bigger body style, and Buick and Olds counter parts came with a 307 Olds motor maybe? I agree bolting it in would be the easy part. On the car I saw it used the cars elc. The motor was just replaced from oil pan to intake. The only thing I remeber was the small frezze plugs where the port fuel injectors used to be. I just thought it might be an option for him to bolt in a 4.9 port FI in place of his 4.1 TB. I would keep the elc. that the car came with, just change the motor. Again, I'm no expert, and its been a few years since I saw that car, but as long as it would bolt in the frame and bolt to the trans, reuse the TB, or maybe change the intakes, keep the dis and the the other sensors, I think it would work. It sounds easy enough, but I know these kind of swaps run into little problems, so more research would be best to know for sure.
The 85 Buick Riviera shared the same platform & had a 3.8L turbo option. you are asking for a lot of time & money hassle to pull something off. I don't no if a 4.5 or 4.9 would bolt up. It may.there is a stick on this subject in the technical section I think.
The 85 engine faces forward like a rear wheel drive car. the 86 up cars had an engine facing the right fender. no way to mount the water pump fan to the later engines for one thing among many others. You would be better off using a 3.8 Buick from a Riviera or an Olds engine from 307 to a 455 from a rear wheel drive car. Best to get an 83 to 85 front wheel drive diesel donor car for the Olds swap (Eldo, Seville, or Riviera, Toronado) That would give you the proper oil pan, oil pump pick up, alt. and A/C mounts exhaust manifolds and engine mounts and be carburated not injected.
85 eldo. nice car. james caan drove 1 in the movie "thief". very boxy styling and the interior/dash is also very crude. but the body had nice clean lines. trying to find parts to fix a motor or maybe do an engine swap is only going to get harder as old parts cars fade away.
After looking at those pics I remeber them better now. The 85 with the forward facing motor could cause some swap problems. The car I saw was an 88 and up 2nd gen car with the transverse motor. I don't think the oil filter is even in the same place on a forward facing motor compared to the side ways mounted motor. That car would be different with a 3800 in it. One out of a newer Park Av. Ultra or a SSEI Bonnie with the supercharger would be nice. It seems like it would take a whole doner car with the wiring harness and all to do a complete swap. Who knows how hard it would be intergrate it to car. If you really didn't want another 4.1, the Olds swap with a carb. sounds good too.