1991 Camaro RS 3.1 to 5.7 Vortec swap

Hey Guys. I’m getting ready to buy a 350 SBC 5.7 Vortec for my 91 camaro to upgrade. I’ve been doing a lot of research on what all will need done. I’ve been hearing a lot of conflicting information on what will actually need done. i’m going to go over what I’ve heard and hope I can get some clarification from some people who have done this before.

The biggest thing for me is the ECM. I’ve heard the original can be reprogrammed to work with the 5.7. I’m not sure if the original will work and if so what all would need done for that. I also wonder about the wiring harness if I would need a new harness as well.

I currently have a 700R4 auto Transmission and from what I’m reading that should bolt right up to the new engine. I’m not sure how well it will handle the added power in this car.

From what I understand, I will need to get V8 motor mounts that should bolt right up to the subframe since these camaros did support the 5.7s.

I know at some point the rear end will probably need upgraded to handle more power.

I plan on labeling all sensors since I’m hoping they will all be or at least most will be compatible with the new engine.

I’m not sure about accessories such as power steering, AC compressor and the alternator. I’ve heard most will be compatible with different brackets.

I’ve heard that the 3.1 radiator should be compatible with the V8 radiator.

Another biggie is that I’ll need to upgrade the front springs to support the heavier engine (This will need done anyway since my shocks aren’t the best right now)

I’m not sure if a different starter would be needed although I wouldn’t think so if both engines can bolt to the 700R4 transmission.

I may be forgetting things and I may be way oversimplifying the project. If I am please and input I can get would be very helpful. Also any additional tips to help make the project easier for myself I’d love any assistance. Thanks Guys!

From what the seller told me this 350 came out of a 97 CK3500 truck.

I believe the computer will be totally different. 1991, the transmission was vacuum controlled, 1997 the trans is controlled by the computer. 1991 was the obd 1 system, 1997 would be obd 2. So working that out may be the biggest issue. I don’t think the GM computers could be programmed in 1991. I think they actually had a chip inside the computer that was different for V6 and V8.

As for the rest, if the motor bolts to the trans, the 700r4 was used with the 350’s anyway. The internals might be different for a v6 vs V8 specific trans, though. Not sure.

I can’t be of very much help. But good luck… I’m afraid you might need the donor truck’s wiring harness and computer, though.

1 Like

that’s agood point regarding the ECM. Unfortuantley. I don’t thni kthe guy selling the engine has the harness or ECM to sell with it.

The main thing for me is have you actually heard this engine run? The world is full of people selling “good engines” when they are anything but.

Hate to go through a lot of work only to find that it has a rod bearing knocking or burning oil like crazy.

You’re not going to be happy putting a medium duty truck engine into a car.

A low RPM, high torque engine isn’t going to perform very well in a car.

Like @Scrapyard_John said, you will need the complete engine wiring harness, and computer.

The wiring is going to be a nightmare with the ODB 1 car and ODB 2 engine.

1 Like

I have not. The cost of the engine was 250 that we talked down from 350. But definitely i had apprehention about.

I was thinking alot more about that and I do believe I’m going to disreagrd this engine. I would definitely appreciate any advice on what engine would be a good alternative.

Forget changing the engine . Just rebuild the one in the vehicle and put the thing in as good a condition as you can afford and it will be appealing to more people if you decide to sell. Engine swaps are not as simple as the TV shows make it look like.

The stuff you don’t have to change… the rearend is fine and the power steering pump, too

The 700R4 won’t bolt to the V8, I am pretty sure it has a different bolt pattern
The 3.1 radiator won’t cut it
The 3.1 wiring harness won’t cut it, 6 injectors vs 8, different placement of sensors
The 3.1 ECU won’t cut it, needs a new chip, the chip is no longer available
The power steering will need a new bracket
If the engine has an alternator, try to use that and its brackets but don’t be surprised if it is in the wrong place
You will need new engine mount brackets
You will need new AC brackets IF the ones on the V8 place the compressor in the wrong place
You will need a different starter than the V6

Given the age of the vehicle, you might be better off going to a carburetor. Making all the other stuff in the car work, will be an issue. Like the speedometer as it needs an ECU to drive it. You might be able to use the ECU to run the stuff you need but not run the engine. Aftermarket fuel injection systems will work well but won’t interface with what you have.

That cheap $250 engine is going to cost you about $3000 (if you bargain shop) to put in. Don’t kid yourself, this isn’t 1967 when an engine swap was easy.

Thanks for the advice man. I think I may stick to doing a manual swap for now. I know there’s stil a decent amount of work involved ut nothing compared to a project like this t seems. I can also focus on just doing performance upgrades to the 3.1

The biggest bang for your buck would be a 4:10 rear axle ratio swap. If it doesn’t have a posi, add one with the new gears. I’d suggest a Tru-Trac gear type if you are buying new or if you can find a Torsen out of a 1993 and up car, that is a great swap.

The axle assembly itself will swap but they are nearly 4 inches wider at the wheel face so your rear wheels will need to change to 50mm offset wheels. The fronts need to stay 0 offset.

Even the 3.1 will chirp tires hard on a 1-2 shift with the automatic. Of course the speedo will read incorrectly. That requires a chip change… You might find one at Hypertech, they used to supply lots back in the day.

Sweet. I’ll keep that in mind. I’ve been reading that the T56 transmission is like the best manual tranny for doing a manual swap. Do oyu know if ti requires any modification or could i just do a direct swap? or if there’s a better manual tranny to suggest?

A T56 is overkill for a V6. I think finding a bellhousing to bolt it up could be difficult and or expensive. The trans is also expensive.

A V6 Tremec T5 is relatively cheap, light and capable of dealing with the V6. The V6 version won’t handle a V8’s torque so they are cheaper. Bellhousings can be found in early S10 trucks. The 60 degree V6 has a unique bellhousing bolt pattern. The bigger versions, the 3.4 liter V6, use the same bolt pattern as a 3.1 in later F bodies.

Why won’t the 700r4 bolt to the 350? Since GM used the 700r4 behind the 350 in some applications? I’m not arguing, just curious. Kind of a moot point anyway as I think getting the 350 in the car and attached to the transmission would be one of the easier parts of the project. Getting everything to communicate and function is the part that’s going to be the deal breaker, in my opinion.

It might be even easier to just swap in an entire 6.0, 5.3, or 4.8 truck engine, transmission, and harness. I think that would be the ticket. The fab work for mounts and what not would be more difficult, and I have no idea how you’d get the gauges to operate, but it’s a popular swap and I imagine the aftermarket would have you covered.

Why are you doing it? V8 is cheap? Current motor is shot? Bored?
Sell car and buy a z28? Stubborn?
I would say buy a 305 Camaro but they are barely better than a v6

Unfortunately I was dumb and bought the camaro from a dealership so i paid way more than I should’ve. that being said the car is in pristine condition otherwise. The Engine is actually fine. but I am still making payments on it for the next year or so. Also being said. This camaro has become my baby and I have no intention of giving her up.

The 3.1 V6 is a 60 degree V6 that was originally designed for the Citation. Yeah, Citation! It has a narrow bolt pattern that is not the same as the V8 or even the 90 degree 4.3 V6. Since his car came with the V6 and the 700R4, he has the V6 bolt pattern, not the V8.

I did the Google thingy ( How hard is it to convert automatic to manual ) . I found an article by a person who made a very good explanation of just how difficult this could be and why it was not really something that would gain enough to justify the cost.

The more I look at it the more I’m inclined to agree. Like i said the more I research the more i find conflicting answers. but one of the more consistant things is people saying it’s probably not the best idea.