What stuff is needed for a 3.8->4.6 swap?

[LoganB]

Hey guys! Ive got a 1997 thunderbird LX. As the title suggests I want to replace my 3.8L with a 4.6L, nothing is confirmed yet but I might get access to 2 donor cars, last time I saw them they were very torn apart, especially in the interior. I want to make a checklist of everything I would need to pull the engine out and put it in my thunderbird.

As far as I know I will need the engine, transmission since it’s a different bolt pattern (but I heard you can get adapters) as well as all the computer stuff and wiring. I also know that the rear end in the 3.8 is a 7.5 diff and the 4.6 is a 8.8. Does anyone have any experience with this type of swap? I want to make a VERY detailed checklist, because I don’t wanna need to find out the hard way I’m missing something crucial.

I’ve seen similar people asking about this swap and the usual response is just « it’s not worth the effort » or « save up and buy the 4.6 version ». For me this isn’t exactly doable, I don’t really have the money and almost all of my money is going to be going to university. The 2 donor cars I’m talking about would also be free or very cheap. I also think it would be a fun project, as long as the budget allows it to be. Which is the reason I want to make sure I have everything I need and don’t need to buy too many extra things or go scavenging for parts.

As for restoring either of the 2 donor cars, also out of the picture. They’re way too torn down, and the one I have is in extremely good condition when it comes to the body and rust and all that

I also have yet to get confirmation that either of the engines even turn over XD so that’s the first step in my checklist!

 

[Rodeo Joe]

Welcome to BirdCats!

Are the donor cars MN-12s and what years are they? If they are MN-12s you can just pull out the V6 related parts and swap in the V8, but there are wiring differences between them. I've swapped the 7.5 out of mine with an 8.8 and V8 axles, pretty straight forward.

The experts can add more to help you out.

Joe

 

[LoganB]

Yes they’re mn-12s, all 3 cars are thunderbirds of the same type, mine is a 1997, both of the others are 1996. only difference is the engine really

 

[theterminator93]

You'll need to transfer over a bunch of stuff.

PCM
PCM harness in the dash
Engine harness
Drivetrain (engine, trans, drive shaft, differential and half shafts)
Fuel pump recommended
Motor mounts
Power steering lines
Transmission cooler lines
Radiator and hoses
A/C lines
A/C condenser (they're different 96/97)
Throttle cables (including cruise control module and cable)
Exhaust

With all the cars being 96/97s you shouldn't need to worry about the TPS, IAC, CPS or ECT sensors or needing do adapt the harnesses because everything is OBD-II already.

 

[LoganB]

Thank you very much! This is exactly what I needed! Before I start the project the first thing I will be checking is if all of this is still in those parts cars. Thanks again.

 

[Grog6]

I would find a 02-2002 crown vic engine and transmission, a 93 mark 8 driveshaft. a 96 mn12 4.6 fuel rail and valvecovers,
harnesses, and maf.
What catchcode are your eec's?

 

[3_97_Sports]

I would find a 02-2002 crown vic engine and transmission, a 93 mark 8 driveshaft. a 96 mn12 4.6 fuel rail and valvecovers,
harnesses, and maf.
What catchcode are your eec's?

He said he has no money to buy all that stuff, he just wants to use the parts cars he has access to.

 

[Rodeo Joe]

Do you know if the donor cars have good engines and transmissions? It would suck to do all that work and find out there's a problem with them.

Greg, both donor cars are 96s.

Joe

 

[LoganB]

Do you know if the donor cars have good engines and transmissions? It would suck to do all that work and find out there's a problem with them.

Greg, both donor cars are 96s.

Joe

Not yet, both cars are 2 hrs away near my grandfathers house, they belong to a relative of ours. If I can get permission I’m gonna go check them out and see if they run or not yet. It’s as you said it would suck to find out they’re bad after doing all the work so I’m going to see if I can get one of them running for cheap before taking out the engines from the car.

As for the transmission I don’t have a clue how I could go about testing it, I think I’d need to test drive them, which would take a lot of work considering the state of those cars

I’m visiting him tommorow so if all works out I should be able to look at them soon hopefully

 

[theterminator93]

While not a surefire way to verify, the transmission fluid can give you a lot of clues. If it's dark, smells burnt and/or has a metallic cast to it it may be a sign of possible troubles. Clean, bright red fluid is ideal.

 

[Grog6]

While not a surefire way to verify, the transmission fluid can give you a lot of clues. If it's dark, smells burnt and/or has a metallic cast to it it may be a sign of possible troubles . Clean, bright red fluid is ideal.

Agreed. That would eliminate one quick. With two donors, I'd use a tube and take a sample from the bottom of the pan of both the trans and the engine oil. Put it in a clear jar, and see if it forms layers. Pour the samples thru a coffee filter, to look for metal. Milky-looking fluid is bad, in either one. But worse for the trans.
The easiest way to evaluate the engine/trans combo, is to get them running. I'd start that by finding out why they're parked, how much gas is in them, and how long they've been sitting.
The eec catchcode is under the hood, pass side, on a sticker, just under the end of the weatherstripping . My 97 tbird was FTE1
The reason I ask is there are codes that seem to cause problems.

 

[MadMikeyL]

If you have the complete donor car, the swap isn’t that difficult, just time consuming, but if you’ve got donor cars and nothing but time, it is pretty straightforward. Only things I haven’t seen mentioned is the driveshaft is a different length between the 3.8 and 4.6 cars, and also the instrument cluster changed between 96 and 97, and sometimes the tachometer is different between the v6/v8 cars, or sometimes there is an extra wire going to it in the V8 harness, but since both donors are 96s, you won’t have a V8 97 cluster or dash harness, so you will have to figure that out. It won’t stop the car from running, but unless it is addressed, the tach will read 33% high.

 

[dDUBb]

I don’t really have the money and almost all of my money is going to be going to university.

If there's nothing wrong with the 3.8L, just leave it alone.

 

[MadMikeyL]

Another alternative, rather than going through all that work, if I had a clean 3.8 car that I wanted to get a little more out of, I would probably do a 4.2 split port swap. The 4.2 was rated around 200hp, which is practically equivalent to the 205hp of the 4.6. 4.2 F150 engines are ubiquitous and dirt cheap in junkyards, and you can use the intake manifold from a 99-04 3.8 Mustang, which is also dirt cheap and ubiquitous in junkyards. That would get you almost the same hp as the stock 4.6, but would allow you to leave the rest of your drivetrain alone, and could be run on your stock computer and wiring harness, with only a tune and some minor wiring modifications.

 

[XR7-4.6]

I never got a chance to verify this but the 96-97 EVTMs strongly hint at it; there’s a chance the EEC harness(the one that the EEC plugs into, passes through the firewall, goes to the engine harness as well as over the shock tower to the CCRM et al) is the same V8 or V6, with the extra injector wires and coil wire there but simply left unused. If that’s correct you can literally plug the V8 EEC and engine harness into it and that is all there is to the wiring.

I kind of tend to agree leave the V6 car a V6 car but if you have a whole same year doner it wouldn’t be terribly difficult to pull this swap off

 

[Grog6]

The swap is a bitch, Are the donor cars fixable, or were they rusted out? Way easier to fix one, than swap a iron v8.

 

[LoganB]

The swap is a bitch, Are the donor cars fixable, or were they rusted out? Way easier to fix one, than swap an iron v8.

They’re rusted out, and half way parted out already

Another alternative, rather than going through all that work, if I had a clean 3.8 car that I wanted to get a little more out of, I would probably do a 4.2 split port swap. The 4.2 was rated around 200hp, which is practically equivalent to the 205hp of the 4.6. 4.2 F150 engines are ubiquitous and dirt cheap in junkyards, and you can use the intake manifold from a 99-04 3.8 Mustang, which is also dirt cheap and ubiquitous in junkyards. That would get you almost the same hp as the stock 4.6, but would allow you to leave the rest of your drivetrain alone, and could be run on your stock computer and wiring harness, with only a tune and some minor wiring modifications.

Il take a look into it, if I can find one in solid condition for cheap it might be a better alternative.

 

[LoganB]

Well I thought about it a decent bit and I convinced myself out of the idea, while I want a v8, for the effort required to take one of the ones out of the other 2 birds and put it in mine would take the same ammount of effort to put quite litterally any other engine in it. I’ve decided to put the whole engine swap idea on hold (might come back to it in a few years once I have the $$) but for now I’m going to focus my energy on other parts of the car. Then when I have some extra freedom maybe I can do a bigger and better swap

 

[theterminator93]

Seems like a sound decision. On the plus side, the reduced weight of the 3.8 in the MN12 is honestly the best combo for handling. They are noticeably more nimble than their 4.6 counterparts.