'83 Monte Carlo V6 to V8 swap

[Monte Cristo]

So, my Monte has been sitting in the back yard for years. I finally have time to replace and upgrade the engine. It came with the factory stock 229/3.8 V6, and and 250C THM transmission. Short term, I want to get a V8 in it to get it mobile, (which it presently isn't). A 305/5.0 was a an upgrade for the year, but from reading the boards, the 350/5.7 is the preferred hot rod. I am assuming that both will work with the 250 C THM, which should get a rebuild. (At least until I can find a good THM 350) I have read that I can get something out of a junk yard cheaply, hopefully with all of the needed brackets, etc. I don't need street legal now, just mobile. What do you recommend I get?

Should I replace the springs and rebuild the suspension now too if I have the time? (It's not a priority.) How much easier is it to do that with the engine out? The body still needs a lot of work, addressing rust problems, etc.

 

[Monte Cristo]

So, I can get a 350 from a truck with a Turbo Hydra-Matic 700R4/4L60 transmission.
How difficult is it to fit that transmission into Monte? (I understand it needs to be shortened).
How big of a problem is a 4 speed transmission install when the gear stick is only 3 speed? I am trying to keep the look as stock as possible. Does the gear shift need to get moved to the hump on the floor?
Thanks!

 

[malibujustin]

If you just want to move it around, what is wrong with the v6 for now? But if you are going to go v8 no time like the present. The 305 and 350 engines will work. In the long run if your planning on more power the 350 would be a better choice. I'm sure you will have to get different mounts. They bolt to the frame differently I believe. It would be good if you found a motor at a yard to get all the accessories. Then you will have them if needed. And if its computer controlled engine you will need some wiring and ecm from donor car if keeping the efi. Not sure of any length differences between the 250 trans and the 350 trans. I do think there is a difference in the 700 trans in length. And mounts. Maybe someone else will chime in too.

 

[Monte Cristo]

The plan was always to put a V8 in it. I can see no real benefit to replacing the V6. I wanted to keep as much of it stock as possible as a restoration, but the 350 is about the same weight as the 305 with much more power. For $350 I can get an entire working engine with the exhaust manifolds. I need to know what to do with the ECM. Hopefully, I can just bypass it as it is off road for now.

So, that is a no brainer, especially if it works with the 250C transmission. (The THM 350C and 250C are outwardly almost identical. The THC 250 is just missing some internal gears.) I wasn't looking to upgrade the transmission now, but I need to know what my options are if I want to upgrade to something newer than the THM 350C. I have seen some good other threads, but they don't mention cosmetic issues for keeping the stock lock. All comments are appreciated.

 

[malibujustin]

If it was a plan to do...go for it. Can't go wrong with the tried and true 350. If your going old school carb you can ditch the ecm. I'm not familiar enough with some of those trans. I know about powerglides, th350, and c4 ford. I have heard good things about 700 trans. I do like the fact that you are trying to keep it stock appearing

 

[Monte Cristo]

The engine on offer should have TBI, so bypassing the ECM should work short term to get it mobile. Stock on an '83 305 or 350 would have been a Rodchester Quadrajet E4ME feedback carb with all of the electronic controls connected to the ECM. I still have the stock Rodchester Dualjet E2ME 210 somewhere from the 229/3.8 V6 engine. I rebuilt that around 1995 or so, which was a major pain in the *ss from the added gizmos for the ECM . As much as I want to keep a stock look, all of the pollution control spaghetti is a major hassle to work around, breaks easily, and performs poorly in comparison to later technology. Putting a plain 4 barrel carb on it would work in a pinch.

 

[Bar50]

You can make the TBI motor work, takes a sort of special intake for 86-up heads. The center two bolt holes on the intake are canted at a different angle than the rest and or traditional small block Chevy. The ONLY 700R4 to get will need to be the style with a TV cable, up to 1991, 92 is a change over year, 93 and later is the 4L60E, same hard parts, but requires a controller to shift. If you do go with a 700R4 you will NEED the cable and assorted brackets as the geometry needs to be correct.

There is more to the difference between 250C and 350C and anyway. The 700R4 requires modification of the driveshaft and the transmission crossmember.

The path of least resistance is to find a car that has needed donor parts. No G-body came with a 700R4.

If you get the TBI motor, get all the accessories, like the alternator, brackets, A/C, power steering pump etc. Keep the engine side of the motor mounts from the V6, as truck mounts (clamshell) are taller and will not work. Or secure car engine side mounts from a V8 SBC Camaro/Firebird. Make sure you get a 5.7, nothing wrong with a 5.0 (305) but, it falls under the same heading as swapping in the V6. I do not know if TBI exhaust manifolds will fit a G-body, Camaro/Firebird will and 80's trucks with the spark plugs under the manifold will.

Do some surfing on local classifieds apps or sites or social media. Salvage or junkyard trips. Late 80's trucks and Suburbans for a heart. TH350 are not as common as they once were. If you go look at one, fluid needs to be bright blood red and have no burnt odor (like hot brakes or clutch smell). No electrical plugs in, that is what makes a TH350-C lock-up (avoid if possible).

 

[Monte Cristo]

So about 15 years ago, my Monte got towed into the back yard to keep it out of sight from vandals, thieves, etc. It hasn't run since 1996. Despite the fact that I kept it covered as much as possible, I still got a complaint from the neighbors to the local municipal authorities calling it a nuisance. They lost. Notice the creative screen so they wouldn't see my antique piece of classic Americana. Last night around 9 PM I heard whooping and hollering as he finally noticed that I had moved the car to work on it. When we moved into this neighborhood 35 years ago, there were quite a few old cars in peoples back yards. Now, they have ordinances against that.

When we moved the car, the brake hydraulics still worked! I must have done a great job on that circa 1995. The bottom of the car does have some rust issues that I need to address. My experience was keeping the mechanical parts of my 80's relics on the road. The body work was done when I sent one to the shop for a paint job or touch up. Now I am going to need to do much more rust-proofing and slapping some Bondo in the holes until I get to welding more permanent solutions. The interior is still in good shape.

The donor engine is a 350 with TBI from a 1990 Chevy pick-up. (A Silverado I was told.) It came with a clutch, which I removed since the photo. Hopefully that will match up with the THM 250-C and flex plate. I need to take one of the heads of to take to a machinist to remove a broken exhaust manifold bolt. Since the heads are steel, it was probably just over-torqued. My other concern is the fuel system. Either I get the rest of the computer electronics to match the engine, or just put a carb on it. I did find the 2 barrel carb from the 229 ci/3.6L original engine. Does anyone think that would work short term to move the car around the yard?


What to do with the old 229 ci/3.8L cadaver? It's quite rare, but likely worthless except for scrap metal.

 

[Ribbedroof]

If you're going to run the 250C/350C, you'll need a flexplate for the 90 engine. It will have a 1 piece rear main seal, which requires a different flexplate than the old 2 piece main seals. 250C or 350C are fine for a driver, but not really desired for performance use, as mentioned above. Either can be run with the lockup unplugged.

BTW, a 229 is a 3.8 litre, not a 3.6

Easiest solution is to making it run is change the intake to a carb intake.

I don't endorse the following method, but have seen it done....
For the center 2 bolts on each side, you hog out the holes so bolt will pass through at correct angle, then use an old rocker arm ball under the bolt head round side to manifold with a flat washer under the bolt head. Will require longer intake bolts, obviously. Would work for moving car around, but would not be my ideal long term solution. Upside is would allow the use of an OE intake, which are usually pretty cheap (sometimes free).


229 carb should be a dual-jet (front half of a Quadrajet). I would bet that you could get a DJ SBC intake for nothing, if anybody still has one. (There's one on my car now, actually, but still in use). Again, carb is not ideal, but should work OK for moving the car around.

Of course, installing the TBI engine is going to require installing an electric fuel pump, as there is no provision for a mechanical pump on the engine, despite the appearance of a pump mounting cavity.

 

[Monte Cristo]

Easiest solution is to making it run is change the intake to a carb intake.

I don't endorse the following method, but have seen it done....
For the center 2 bolts on each side, you hog out the holes so bolt will pass through at correct angle, then use an old rocker arm ball under the bolt head round side to manifold with a flat washer under the bolt head. Will require longer intake bolts, obviously. Would work for moving car around, but would not be my ideal long term solution. Upside is would allow the use of an OE intake, which are usually pretty cheap (sometimes free).

229 carb should be a dual-jet (front half of a Quadrajet). I would bet that you could get a DJ SBC intake for nothing, if anybody still has one. (There's one on my car now, actually, but still in use). Again, carb is not ideal, but should work OK for moving the car around.

Of course, installing the TBI engine is going to require installing an electric fuel pump, as there is no provision for a mechanical pump on the engine, despite the appearance of a pump mounting cavity.

Thanks!

It's going to require an electric fuel pump regardless now. I need to think about the intake bolts and manifold. Dunno how difficult it would be to get the TBI to work.

BTW, a 229 is a 3.8 litre, not a 3.6.

Thanks for catching that. I had it right in the first post, and then wrong later. The important part is that in is the 229 and and the 231, which appears to have been more popular. Someone is still selling these remanufactured and charging $350 for the core. There must be some market for the old junk somewhere.