Oldsmobile V8 interchangeability

zipties

Apprentice
Feb 2, 2022
52
18
If you've seen my other posts recently you know the jist of my situation. I'm in the process of getting my barn find, poorly maintained 79 cut back on the road. Timing chain killed itself.

I was originally planning on fixing it all with the motor in the car, but I know that it's a half measure and now that I've saved some money back up, i wanna do things right.

I'm in the process of sourcing another motor for it - i wanna keep it Olds powered for now. Just wondering what potential parts i'll need to change to make them work - motor in it now is a 78 350, i'm looking at pretty much any v8 that isn't totally anemic or not much better than what I have now.

I'm going to look at a 70 455 soon which is a big step up and not exactly my first choice, but these things are hard to find up here. My usual spots came up dry unfortunately. it's my first serious lead on a motor.

I assume mounts and manifolds aren't different, but what else do I need to consider? I have a 600 holley, guessing that may be a little small for a 455.

Any advice greatly appreciated. here's a pic of the motor im interested in right now. Only other one i've seen is a 260 which is almost three hours away.. everything else is a pile of parts or needs serious work.

Screenshot_20220703-220554_Facebook.jpg
 
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Ugly1

G-Body Guru
Oct 26, 2021
591
63
Lost in the woods of NH
Can’t remember if there is a wgt difference of much between the SBO and BBO. last couple of motor change overs (many moons ago) was V6 Buick to BBO, so springs got changed. But if front springs are old…you may have to allow for the taller deck so carb sits higher.
 
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Oct 14, 2008
8,183
113
Melville,Saskatchewan
A pre 77 350 or a 403 is a good choice. The SB 260, 307, 350 and 403 directly swap with each other. The BB 400, 425 and 425 will fit but intake and air cleaner selection must be right to fit under the hood. Also the R4 A/C brackets are 260 through 403 only and must be modified to fit the BB, due to the taller deck height. Yes, that 600 Holley is way too small, even a 750 cfm is too small. That factory Qjet on the 455 is a good carb and tuned to that motor. Good luck and stay Olds powered👍.
 
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zipties

Apprentice
Thread starter
Feb 2, 2022
52
18
A pre 77 350 or a 403 is a good choice. The SB 260, 307, 350 and 403 directly swap with each other. The BB 400, 425 and 425 will fit but intake and air cleaner selection must be right to fit under the hood. Also the R4 A/C brackets are 260 through 403 only and must be modified to fit the BB, due to the taller deck height. Yes, that 600 Holley is way too small, even a 750 cfm is too small. That factory Qjet on the 455 is a good carb and tuned to that motor. Good luck and stay Olds powered👍.
Yeah, woulda have preferred finding another 350 or even a 307, trying to make the thing a solid driver. can't imagine what kinda fuel economy im gonna manage with a big block. with how gas is, its not a very attractive option, but better than no motor at all.

hood clearance aint a concern since i have plans for a cowl/scoop. carb stud already sticks through a trim hole...

im not running A/C since it was missing from the start, not a concern, but is the rest of the acc drive from the 350 a match? Alt and PS pump.
 
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Ugly1

G-Body Guru
Oct 26, 2021
591
63
Lost in the woods of NH
A pre 77 350 or a 403 is a good choice. The SB 260, 307, 350 and 403 directly swap with each other. The BB 400, 425 and 425 will fit but intake and air cleaner selection must be right to fit under the hood. Also the R4 A/C brackets are 260 through 403 only and must be modified to fit the BB, due to the taller deck height. Yes, that 600 Holley is way too small, even a 750 cfm is too small. That factory Qjet on the 455 is a good carb and tuned to that motor. Good luck and stay Olds powered👍.
Q-jet 800 cfm is able to satisfy the BB. Sold off 3 that needed rebuild for $25 each. Was sad but brother needed any money he could for hospital bills.
 
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Oct 14, 2008
8,183
113
Melville,Saskatchewan
Yes the other accessories should work. Just make sure you have the triple crank pullies to drive two belts off the crank.
 
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78Delta88

Master Mechanic
May 23, 2022
315
43
SW Arizona
Deck is 12 inch across intake manifold on the 307/350 and 14 inch across the intake on the 455.

What are the head numbers on the 455 you are showing. 1970 is pre-smog and the "G" heads were in hot demand a few years ago. Some went 1,000 each, from what I was told. Can you post pic of the head ? Casting number is up front on side of head near number 1 exhaust.

455 is a torque monster which is why they were used for speed boats.

260 is useless to build but good for parts.

307 not bad basic engine but limited just like SBC 305, but 307 parts interchange with 350 except for pistons.

Most all the engine parts exchange across the platform. I have 307s. And know where some 350s are.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,654
113
Make sure you know the year of the 307 once you start piddling around looking. If someone offers up a 307, look for the A5 intake and 7A heads. If you see those, it's a decent engine, but has peanut ports. NOT a good candidate for performance. The plus side is it has a roller cam. The roller engines came on everything but the 85 442 starting in 1985. 85 442 ran with essentially the same engine as the 84 H/O, with a flat tappet cam, but that was it.

If you go with the 455, you probably won't find reasonable priced headers for it. For the street, you'll probably want to stay with 442 style exhaust manifolds. Cowl hood is a good idea as it wipes out any concern for hood clearance, which would be tight with a stock hood. Depending on clearances, it'll be tight over by the HVAC housing and valve cover too, but it should barely clear. PITA to change #8 plug though, from what I hear. But if you use the SBO mounts for it that you have now, you should fit in a 455 rather easily. If you use a 200-4R behind the 455, you MUST build it to take the extra torque or you certainly will be looking for a new transmission later. It's a fairly tough transmission, but not that tough.

EDIT: When I mentioned exhaust manifolds, I meant the cast iron OLDER 442 style. You can probably get by with the older downpipes from the 442 as well, but likely will need to fab up the exhaust from there on back to fit the shorter wheel base of the G-body.
 
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Oct 14, 2008
8,183
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Melville,Saskatchewan
69Hurstolds, I agree completely. Do you know that a class racer with the swirl port 307 claimed no one used the 5A heads in class Racing, which I know isn't true on Classic Olds. I asked for flow numbers and work done. He was vague and didn't have the flow numbers on hand. I saw a flow test on the old Oldspower for stock 7A heads. It was like 130 and 100, horrible. I mentioned the numbers he said his was more like 160 for his. Obviously improved but he didn't say how. All I know anytime someone complained about a slow 307 when these cars were on the road, it was the swirl port 307.
 

Clutch

Geezer
Apr 7, 2017
5,067
113
Brick NJ
Imo for a stock ish 455 swap use the w z A-body 442 manifolds. When I first did my 87 cutlass I used everything off the front of the 307 out of it for the change in deck hight I used a craftsman socket as a spacer between the alternator bracket and the power steering bracket and for the A/C bracket I sawed 2 307 front brackets in half and welded them back together to gain the 3/4 inch hight difference. I know there's some different accessory bracketry and 79 but I think if you think outside the box you can make it work much like I did with my 307 to 455 swap. Your small block mounts go right on and locate the 455 perfectly. As for your trans if you just go easy and drive it it will stay together for a while. When I first went 455 I had a 200m and 4;11 gears and posi with 29.5x9-15 m/t wrinkle walls so my 200 lasted all of 1 launch on hot slicks. Then I went th350 bone stock lasted 1 weekend. I decided I wanted OD so I got a GN 200r4 ripped the sun gear out of it did a short stint th400 now it's got an M-21 welcome to the sledgehammer torque club! Lol personally I would run the quadrajet carburetor that's on the 455 just do a rebuild and as far as mpg stay out of the secondaries you'll be fine. The car is light and the motor makes a boat load of torque so it doesn't have to work hard to get it down the road under normal driving conditions.
 
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