Engine Swap Choices (Page 1/1)
Pengu MAR 21, 03:12 PM
Hello, I have recently bought a 1986 Fiero GT Auto, which runs and drives OK but was hoping for an engine and trans swap. I've also recently received a complete 2004 Grand Prix with the 3800NA Series 3, about 140k miles. I am mainly interested in reliability and gas mileage, as I'd like this car to be my new and constant daily.

However, I know a Series 2 swap is easier than a Series 3. There is currently an offer for $600 3800SC Series 2, also 140k miles, with all necessary wiring/computer/ etc. Should I stay with the 3800NA Series 3 I already own, or buy the 3800SC series 2? With the main concerns being reliability, gas mileage, and ease/cost of installation.

[This message has been edited by Pengu (edited 03-21-2023).]

olejoedad MAR 22, 07:58 AM
You can run a series 3 as a series 2, by changing the throttle body and using a series 2 PCM.

Which engine has lower miles?
Pengu MAR 23, 11:28 PM
The NA Series 3. I know the install for the series 2 has been down thoroughly on here, are those two factors the main difference? I remember seeing something about avoiding drive by wire with the Series 3, but if I just need a series 2 computer and adjust the throttle body, I'd be relieved.
Trinten MAR 24, 12:33 AM
Welcome to the forum!!

I believe what olejoedad was inferring is that by swapping the Series 3 throttle body and computer to Series 2, you are eliminating the Drive By Wire.

I think with that, you'll also have to add a few wires to your series 3 wiring harness (and you can remove a few wires as well). The wires you'd be adding are for your TPS and IAC. Please confirm this - I know that's something we had to do when we eliminated the Drive By Wire on my build, though my build is not with a 3800, so please confirm.

There are some very skilled wire harness builders on here that can do (or used to do) a variety of things for you, everything from expertly modding and splicing your harness (including shortening/lengthening things where needed for a cleaner install), up to doing a from-scratch harness, if you don't want to worry about any soldering or butt-splices, etc.

It sounds like you've done some pursuing already. The Search function is good, though can be finicky depending on how you search for things. Another way you can try to search for specific thing is using Google with the site: function. If you aren't familiar, you can start your search with site:fiero.nl (no spaces) and then your query, using quotes where you want to find exact phrases, and it'll only return results from here -- it's been a huge help for me.

If you can't find the answer you need, or worse, the thread is too old and key images are gone, always feel free to ask. While there is a lot retreaded topics, many people here are glad to share their experiences, or point you to a thread you may have missed!

Looking forward to seeing your build/progress!
Corsair231 MAR 25, 06:29 AM
You didn't say what the reason was as to why you want the engine/trans swap. Reliability should be about the same for either platform. If the car is to be your daily and your main concern is the mileage you will pick up due to a more modern overdrive trans, then the n/a swap would seem to be a more economical choice although you will have the extra cost of the parts to switch from series III if you want to get away from the drive by wire. If the goal is to have a more entertaining ride as well as better mileage, the s/c swap might be your answer. Depending on your driving style, the mpg will not be much different than the n/a, and if you decide on upgrading for even more power in the future, you will have the platform to do it already in place. Providing that both engines are near identical in condition and the s/c doesn't need major overhaul, there will still be some cost above just purchase price that you will have to pay, there always is, but that will be mostly the same for either swap. I guess the question is that if in the long run the s/c is worth the $600 purchase price. I think if you look at it as smiles per gallon, that comes out pretty cheap.

[This message has been edited by Corsair231 (edited 03-25-2023).]

82-T/A [At Work] MAR 25, 09:25 AM

quote
Originally posted by Pengu:

Hello, I have recently bought a 1986 Fiero GT Auto, which runs and drives OK but was hoping for an engine and trans swap. I've also recently received a complete 2004 Grand Prix with the 3800NA Series 3, about 140k miles. I am mainly interested in reliability and gas mileage, as I'd like this car to be my new and constant daily.

However, I know a Series 2 swap is easier than a Series 3. There is currently an offer for $600 3800SC Series 2, also 140k miles, with all necessary wiring/computer/ etc. Should I stay with the 3800NA Series 3 I already own, or buy the 3800SC series 2? With the main concerns being reliability, gas mileage, and ease/cost of installation.





There are a LOT of engine swap options... the Fiero engine bay is decently large, so you can fit almost anything in there.

Really depends on what you want to get out of it... whether that is insane 0-60 performance, or you also want it to handle well in corners.

Personally, I like something that's kind of in the middle. One option that I really like is the 2.4L LD9 Twin Cam with the "Secret Cam" swap, mated with a 5-Speed Getrag (one meant for a Quad-4 / TwinCam).

It's a SUPER reliable motor, really winds out, and you can do some really basic performance upgrades to get it to ~180hp very reasonably. With the 5-Speed Getrag, you'll be in the 14s in the quarter, and it'll probably handle better than stock due to slightly improved weight-distribution.


But there's so many other options from the 3800 SC to an LS. A lot of people just swap in a 3.4 V6/60 which looks stock... lots of options.
Pengu MAR 26, 01:42 PM
First off, thank you for these responses. I have attended some nearby Atlanta Fiero Club meetings, so when it gets to the nitty gritty of the wiring harness, I could ask there for help as well. Since I already have the donor car (2004 Grand Prix 3800 NA Series III) in possession, I wanted to confirm that would be the best move, before going further in, as the alternative is fixing and selling the donor car for something else. I will look around the area for any junk yard specials. I've had the Fiero for a few months, and I was able to give a skin deep look to make sure there's no rust. Since I'd like to give the car a full restomod, including cleaning the engine bay, I figured a swap was due.

As a daily that would be seeing majority highway miles, and as my first engine swap, reliability and ease of installation are my main concerns. Given the numerous Series II swap documentations, I believe the Series III shouldn't be too different. I will be able to update the progress as it comes in the next few months, now I'm off to find a proper engine crane.
Spadesluck MAR 26, 02:10 PM
We have a Georgia Fiero Club as well. Not sure if you are part of that.

Georgia Fiero Club
qwikgta APR 10, 08:11 PM
I did a 04 3800 NA in my 88 GT, and like others have said above, I put on a drive by cable TB on it and installed a 03 PCM. You will need the 03 PCM b/c its the first year the 3800 had the newer 4T65E trans. I ended up wiring the 04 motor as an 03 series II and it runs like a champ.






Rob