what is all that is involved in a 350 to 455 swap

my car is the 70 cutlass in my signature

and since the motor in it currently is non op

i was wondering what parts i need to start collecting to make it happen

so please help me get my list together

thanks
shak

 

I don't know half of what some of these guys do, but here's something to consider:

- For the swap, make sure both the motor mounts and frame mounts are from the same block; either BOTH for a big block or BOTH for a small block - I've heard small block engine mounts will fit on a big block and vice versa (someone PLEASE chime in if I'm wrong). It's just that the different mounts won't line up with each other.

- Personally, I'm finding that a surprising number of SBO to BBO parts are interchangeable; heads, cams, etc. The main difference is that the BBO is taller, so I'd stick with a Performer intake and not a high rise (Victor Jr. Torker, etc.) to avoid hood clearance issues.

- Suspension has been argued both ways. The SBO vs. BBO weight is about 100 pounds; the alum. intake will make it about 75; remove your a/c (if you have it) and you're pretty close to even.

If someone else has advice on fuel line size, rad upgrades, etc. I'd like to hear it, since I'm considering the same swap in a '69 Cutlass. I'm guessing this stuff depends on how wild a BBO you're building.

- GoldOlds

 

The BBO and SBO are externally identical except for the deck height. All interfaces (bellhousing bolt pattern, motor mount bolt holes, valve covers, head bolt pattern, water pump, etc) are exactly the same.

You are correct. The motor mount difference is not directly related to big vs. small block but to a motor mount design change in 1969. For 1968 and earlier, the BBO and SBO used the same part number motor mounts.

See my into above. Unlike the SBC and BBC, which are completely different, the SBO and BBO are more like the Mopar B-block and RB-block motors - just big and bigger block motors...

I've installed many a BBO onto SBO springs with no problems. The front of the car sits very slightly lower.

I always to to a 4-row core, but a good aftermarket aluminum will work fine also. The factory 3/8" fuel line is the same on the SBO and BBO, but an upgrade is always a good thing. Exhaust manifolds or headers are unique to big and small due to the deck height differences. Get a high-torque starter.

 

what about the install of a th400 does anything have to be modified to make it fit if your car came with a th350 ?

 

TH400 has a shorter driveshaft and you'll need an electric kick down switch.

C.J.

 

Are electric kick down switches easy to come by ?

 

You will need to slide the cross member back towards rear to the next set of holes. You might have to drill one of them on each side.

 

a type "O" 12 bolt with 2.73 gears should hold up to the 455 right ?

 

also if i get a smog era 455 all i would need to bring the performance back would be heads correct? or are there other things that should be changed as well ?

 

any major auto parts store will carry them.

 

Hey Shaks
I believe the dish (cc) in the piston is larger in the smog engine, hence lower compression. Depending on how many horses your lookin at, you may want to upgrade on pistons. Don't get me wrong, a J headed smog engine can still scoot.

Joe's right, don't worry to much about changing front springs. I have done it with little impact on stance. Good luck with BBO change-over!

Mark

 

Heads will not interchange,intakes will not,headers will but sbo are a miserable fit,buy bbo ones,if you have a th350 build it for your application it will be fine.I did the same swap about 3 years ago in a 71 cutlass convert.My 350 frame mounts very fine with the bbo eng mounts, almost everthing else swapped over with no problem, I did go to an aluminum radiator and elec cooling fans.I also removed my ac and had no difference in ride height between the two eng setups,of course I also went to an aliminum intake.

 

CHRISH8846: I believe that the heads will fit but the problems would be in the valve size on the 350 heads might be smaller. I put a set of heads from a 425 on a SBO (350) and they worked great. Headers might be more specific to the motor and car as I have a 71 cutlass and the headers can be ordered but they are for a supreme and I have an "S" with a 455 in it.
ImWired

 

You may want to consider your power brake system. A-body 455's with power brakes had notched valve covers for clearance to the brake booster. I don't know dimensionally exactly how much clearance you'll have, but, you may want to keep your eyes open for notched valve covers or a slightly smaller than stock power brake booster.
Many 455's are pulled from Delta's and often come with weird passenger side two-into-one exhaust manifolds. You will want to plan on headers or start searching for 455 a-body exhaust manifolds. If you go the header route, you may have to move the brake distribution block to the top of the frame rail, and, convert your tree mounted shifter to floor mount to avoid linkage interference.
Sounds like a pain but there is no substitute for cubic inches.

 

Good luck finding notched valve covers at any reasonable price. The good news is that the regular valve covers fit fine with the original brake booster. I've done this may times on A-body cars.

You WILL need to move the distribution block. No "may" about it.

 

A 12 bolt should be good to around 500 tq so long as you don't run slicks. With slicks, idk. A th350 will hold up fine to about 500 ft lbs tq if built right. Every part but pistons, rods (?), crank, and intake interchange between big and small blocks.