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Discussion Starter #1
Sorry if these have been answered before I have spent the last couple of days searching this forum and others on the topic and I have gained alot of knowledge but I still have a few unanswered questions.

This forum seems to have the most info on the subject so I hope you guys can help.

I have a 1994 Thunderbird with a standard NA 3.8L. I have been having problems with it for awhile most recently the motor mount went out on the left side and it is running rough, all of which could be fixed but with the amount of work I have had to do to it all ready I am exploring 2 options, a swap for a different engine (3.8L or 4.2L) or just selling the car.

I have owned the car since 1999 so I am kinda attached to it and would hate to part with it. Plus I like not having a car payment :D

So now that the boring background is out of the way, on to the questions

1> From the posts the 4.2L seems like a very easy swap, too easy, is there something that I am missing or is it really that easy?

2> Computers. with the 3.8L computer control the 4.2L or do I need the computer from the donor?

3> Intakes. Are there any intakes that you dont have to cut the whole in the hood like pictured in the "4.2L swap" thread? I ask this because in that thread is mentions the Mustangs but then says it will not clear the distributor? but then in the other "my new project" thread he is using a 4.2 lower and a 3.8 mustang upper so will that combo allow for the clearance needed?

4> Performance Aside is the 4.2 a more reliable engine than the 3.8?

5> Any Drivetrain Concerns for the added power? My Tranny has the same miles as my engine (140K or so) should I replace it at the same time I have the engine out?

I think that will get me started

Right now I am just wanting to get my car up and running in tip top shape. I dont know if I should Rebult my 3.8L, buy a 4.2L and rebuild it, or just scrap the car

Thanks
 

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Dim Bulb
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yes it is that easy, a 4.2 is just a stroked 3.8, that is the same block with different heads, rods & I think crank. The EEC for a 3.8 will also govern a 4.2, you'll need a new custom burned chip. I don't believe there's difference in the drivetrain, but for it and the rest of your ?s I'm not positive so I'll keep quiet.
 

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First off, let me start by asking you this: Do you really think it's so hard to change a motor mount that it'd be easier to swap an engine or sell the car? I swapped out not only one, but two engine mounts in 2 hours. That's nothing at all. It's a very easy fix.

But on to the answers...

1. It is fairly simple, depending which route you take, but you can simply swap the shortblocks and keep your heads and intakes to make it even easier.

2. You can keep your stock computer and use a chip to run it, but I would strongly recommend a dyno tune afterwards as well.

3. The 4.2 split-port lower intake has the same height as the 3.8 split-port lower intake, but the 4.2 is supposed to flow better. You can use the mustang split-port intakes and it has been shown to clear the distributor with the deleting of the EGR or a custom EGR tube to clear the distributor. But like I said, rather than swapping to split-port heads and intakes you could keep your stock ones to make it easier and save money.

4. Esentially, the 4.2 is the same as the 3.8, just with shorter pistons and a longer stroke. The rods are the same length as 96+ 3.8's, which are longer than the previous years, which does make them stronger than your current engine. And the 4.2 crank has been put under some extreme power by some mustang guys, so it can handle a lot.

5. I wouldn't replace the transmission just yet, you can do the JMod shift kit and upgrade to imrpove it's performance and prolong it's life along with a transmission cooler, and that should last a long time, though nothing is guaranteed with the earlier year 4r70w transmissions.

But seriously, motor mounts are easy to change. The driver side is a bit harder than the passenger but it is still very easy to replace. All it takes is a block of wood, a car jack, and 3 bolts, then it's out of the car with some maneuvering.

-Thomas
 

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the_ancient said:
1> From the posts the 4.2L seems like a very easy swap, too easy, is there something that I am missing or is it really that easy?

It's only easy IF you know what your doing... Swapping engines is not for the faint of heart. It does require a fair amount of knowledge, time and patience.

2> Computers. with the 3.8L computer control the 4.2L or do I need the computer from the donor?

your standard computer will work fine, but will need to be modified (by chip or a tune) to allow for more air and new injectors

3> Intakes. Are there any intakes that you dont have to cut the whole in the hood like pictured in the "4.2L swap" thread? I ask this because in that thread is mentions the Mustangs but then says it will not clear the distributor? but then in the other "my new project" thread he is using a 4.2 lower and a 3.8 mustang upper so will that combo allow for the clearance needed?

This is the tricky one. There are different ways you can go with this. With the truck intake, you will need a new hood and might have to cut the hood. With the mustang upper intake, you will have the hood clearance you need, but the distributor will interfere with the EGR system.

Now, if you are good with wiring, know your sh*t, you can convert your ignition to a DIS (Distributorless Ignition System) from a 96/97 v6 and eliminate the distributor all together. Racecougar did this, but it was not an easy job.


4> Performance Aside is the 4.2 a more reliable engine than the 3.8?

Reliability is in the hands of the builder and the driver.

5> Any Drivetrain Concerns for the added power? My Tranny has the same miles as my engine (140K or so) should I replace it at the same time I have the engine out?

Yes, there are drivetrain concerns:

  • The stock rear end (7.5") will not hold up to repeated abuse by a stronger engine. You will need to put in a 8.8" rear end for durability

  • The stock rear axles are very skinny compared to a v8's or a SC's axles. You would need to swap to larger rear axles to avoid snapping them.

  • The transmission is a known problem for your vintage of car. I would HIGHLY suggest budgeting for a new/rebuilt transmission. There are a few people in this forum who can help you with that (Darrin and a few others come to mind)


I think that will get me started

Right now I am just wanting to get my car up and running in tip top shape. I dont know if I should Rebult my 3.8L, buy a 4.2L and rebuild it, or just scrap the car

Thanks
You are welcome
 

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Discussion Starter #5
Thomas said:
First off, let me start by asking you this: Do you really think it's so hard to change a motor mount that it'd be easier to swap an engine or sell the car? I swapped out not only one, but two engine mounts in 2 hours. That's nothing at all. It's a very easy fix.

But on to the answers...



But seriously, motor mounts are easy to change. The driver side is a bit harder than the passenger but it is still very easy to replace. All it takes is a block of wood, a car jack, and 3 bolts, then it's out of the car with some maneuvering.

-Thomas
Well if it is was just the Mounts I probally would not consider it, but I think the engine is on its last leg, so.... it is nickle and diming me to death.

but while we are on the subject, I did look at just changing the mounts for the time being, I can get to the Lower Bolt fine, but is there a way to get to the upper Bolts with out Taking the Exhaust Manfoild off or Power Steering Pump off? I cant see a "easy" way to get to those bastards.

If you know a Trick by all means let me know atleast I could drive it until the engine blows out completely then :D

I am not New to removing and replacing Engines, however this would be the first time I would swap out differant size motors. normally I just do direct replacment. but since I read how easy this swap was I figured I would explore that option.

I am by know means a Seasoned Mechanic, but I do know where all the Dipsticks go :D

Thanks for both your help so far.
 

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I got my mounts off with ratcheting wrenches, it's about the only way you can fit anything in there, but it is much easier to do on the 89-95's because the 96-97 tubular headers crowd the mounts a bit more.
-Thomas
 

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Discussion Starter #7
Thomas said:
I got my mounts off with ratcheting wrenches, it's about the only way you can fit anything in there, but it is much easier to do on the 89-95's because the 96-97 tubular headers crowd the mounts a bit more.
-Thomas
I thought about buying a set of those, I have a few that I have picked up but none are the size of those bolts ofcourse.

the Passenger side is easy, is the drivers site that is giving me the problems. either the Steering colum or the exhaust gets in my way. I guess I have to remove one or the other if I cant find another way around to the Back upper bolt.

I will probally try it this week end and just get the motor mounts in and see if I can get some of the other problems solved so it can be drivable

but I still think I am going to put a 4.2 in it, but probally not till next summer, I dont think it will be worth it unless I replace my tranny at the same time, and I dont have the cash to do both right now.

The Engine and Tranny was not well taken care of, (I was 18 when I got the car) and that is what is causing my problems today.

Thanks for the help
 

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I was in the same situation, my transmission is holding up despite all the power I've put into it, and I'm making more than a stock 4.2, though my torque is lower with this turbo cam. I didnt have to remove anything to get the motor mounts out, maybe you should just try harder :)
-Thomas
 
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