View Full Version : 1986 fwb engine swap- 307 to 350 olds

cadillac kevin
01-11-11, 12:20 AM
as noted in my last topic, my cars drivetrain is out of alignment, the trans is most likely fried (it was starting to go out before the accident) and I have lost quite a bit of coolant out of the engine, and the car is undrivable.
so I think this would be the perfect reason to justify a drivetrain swap. I plan on swapping in an olds motor since it already has the mounts, and it will still look stock when I open the hood.
I am sure I'm going with a pre 72 350 or 455, with a turbo 350 or 400 trans, but I have been having problems finding them. I plan on keeping my R12 A/C, heater, cruise, etc.
I would like to know if there is anything I should take into consideration that might not be so obvious when swapping an olds motor for an olds motor.
btw, I'm not made of money and plan on spending $1500 total (hopefully will be having it installed by a buddy with an engine hoist, so installation costs shouldnt come into play too much)
a decent 455 olds motor will cost $800 to $1000 for a long block, and a pre 72 350 will cost $300 (untested/ as is) to $800 (either can test drive before its pulled out, or it comes in a car with horrid body rot) but most are roughly $500 and are complete from carb to oil pan.
is there anything I should take into consideration when doing the swap, any parts I should definitely have taken to a machine shop (besides heads of course), any performance upgrades that should be done now. I should note that I am mechanically inclined, but I dont have tools or space to redo/ machine parts myself, so anything I have done will have to be sent out.
are there any parts I should reuse from the 307. the motor I have in the car runs fine and has under 67xxx original miles, so most parts on it would be reusable if necessary, but the cost of resetting it so it is where it should be would cost nearly as much as just getting another drivetrain and putting it in and I would still need another transmission ($1200 for installing junkyard one- yikes!!)
any help would be greatly appreciated. Also, mileage WILL BE a major consideration, so what mileage can I get out of a mostly stock 350 or bone stock 455 olds motor with a 3 speed auto trans and super low rear gears.

01-11-11, 01:53 AM
I've did both the Olds 350/overdrive tranny swap and BB/3 speed swap and I would have to say the easiest thing to do is probably find a 90-93 Brougham and pull the SBC motor/tranny/driveshaft out and put a carb intake and carb on it and call it a day. Now you have power, serpentine belt, better tranny, bolt in, good gas mileage and no need to mess with your rearend. Find a 90-92 for 1K and you can use other parts off it, stay under budget and still have heat, R12, cruise, etc... Put a cam in it for whipping shitties.

01-12-11, 04:21 PM
And if you do stay with Olds power, you can use all of the accessories from your 307. They will all bolt onto an Olds 350 or a 403. Not sure about a 455, but I THINK they might. Good luck with the swap. Can't wait to get mine going this spring. :thumbsup:

01-12-11, 05:46 PM
The 455 is a different animal. The 307/350/403 all have the same block, so the heads, intakes, and accessories are interchangeable.

cadillac kevin
01-12-11, 09:55 PM
thanks for the info guys.
Now that I want a 350 olds, they seem to have vanished on craigslist. and I found out it will be pretty hard to come in under 2k for a rebuilt olds and a working trans (I'm on a shoestring budget here)
I was talking to my neighbor and he offered me a good deal on a 350 chevy truck motor w/ 4 bolt mains (a great deal considering its rebuilt and was only used in light duty for a couple years)
could I still keep my accessories if I went to a chevy 350. I mainly want to keep A/C since mine still works great, and cruise control is a must considering I drive down the highway every day. the motor is from 1977 I believe.
would my cars computer go nuts without having input from all the sensors the olds motor had?
could I also keep the CCC 4 bbl the car came with?
I would love if it was as easy as you say csbuckn, but cheap caddies dont exist around me. the old caddies are still too popular to be "cheap." mine was a "steal" at $1500, but thats just because it had minor body damage and an uncared for interior. most run 3k on up, in similar shape to mine when I got it, especially for the chevy powered ones.

01-12-11, 10:25 PM
Your a/c and cruise control would not work. If the truck does not have working accessories, you should be able to find everything you need, cheaply, at a local junkyard, and then use your current refrigerant to charge the A/C system.

As for the computer; you are going to be disconnecting it. The ECM is only there for fuel metering, and you cannot use your Oldsmobile E-Carb on a Chevrolet (I tried that). The only thing you will lose by disconnecting the computer is the A/C Compressor Clutch relay, which is grounded through the ECM. To make that work without the ECM, you only need to relocate the relay and supply it with chassis ground. Other than that, you could replace the computer with a rat's nest and never know the difference in your car's performance (aside for the benefits of the new motor) .

cadillac kevin
01-12-11, 11:00 PM
so will the AC compressor on my olds motor not physically bolt to a chevy motor? I would imagine GM used the same compressors across various makes for cheapness's sake, and only the brackets would change
I still have R-12 in the AC system, and would like to keep it that way.
my neighbor said the truck motor is complete, but I dont think it had AC or cruise (it was a stripped down 70's work truck)

01-12-11, 11:42 PM
No the compressors are different...

This is what is on your Oldsmobile:
http://info.rockauto.com/getimage/getimage.php?imageurl=http%3A%2F%2Finfo.rockauto.c om%2FFourSeasons%2F57231.jpg&imagekey=816651-0&width=450

This is what Chevrolet used in 1977:
http://info.rockauto.com/getimage/getimage.php?imageurl=http%3A%2F%2Finfo.rockauto.c om%2FFourSeasons%2F57089.jpg&imagekey=816456-0&width=450

And this is what Chevrolet put on the '80's & '90's 350:
http://info.rockauto.com/getimage/getimage.php?imageurl=http%3A%2F%2Finfo.rockauto.c om%2FFourSeasons%2F58237.jpg&imagekey=815760-0&width=450

On top off all that, you would need to install all of the piping for the refrigerant. The pipes from your Olds will not couture to the Chevy, so you would either have to find NOS plumbing, or have the parts custom made to fit the engine.

01-13-11, 07:08 AM
But.......... the early 80's Chevys used the same compressor as that Olds If Kevin is using a 70's Chevy engine he is correct that he just needs some early 80's chevy brackets for the AC compressor and the cruise control canister too. If the Chevy engine runs nice, like those old truck motors usually do, I wouldn't change that carb either but you may have to drill a hole in the linkage arm for the cruise control.

01-13-11, 12:44 PM
^Your right... The compressors are the same. But that still leaves the problem of getting the piping for the Chevy's A/C

01-13-11, 01:05 PM
I am in the process of swapping my 307 to a 350 but I am having a motor built for 1500 and its comming from a 70-76. I am going to run the 700r4 because of the overdrive feature once I finish rebuilding that with a longer output shaft. Def throw an upgraded cam in it.