Which 3.1/3.4 for swap? (Page 1/1)
CSM842M4 OCT 07, 08:59 PM
Well, I'm about to stick a set of .040"/1.00mm undersize bearings in the big end of the #4 rod in my '86 GT's 2.8, hopefully making it driveable for the short term. Then, I'm going on the hunt for another v6 to rebuild. So, in the interest of making it as quick a process as possible,
1. What donor vehicles should I look at for 3.1- or 3.4-liter candidates? Does it make a difference that I currently have the 4-speed manual transmission and will either keep it or swap for a 5-speed manual?
2. Are there any parts on my 2.8 that would be at home on the bigger engine, or will the fresh engine need to keep all of its native furniture?
3. Is there any special intel that would serve me well going into the hunt and/or the swap?
I really hope I can drive the car for at least a little while with its original engine, if for nothing else than for my "seat of the pants" dyno to have a baseline for comparison. As always, all input is greatly appreciated. Thanks in advance -Chris

[This message has been edited by CSM842M4 (edited 10-07-2020).]

Mike in Sydney OCT 08, 06:31 AM
Look for a 3.4L from a 1993, 94, or 95 Firebird or Camaro. These are darn near drop in replacements for Fieros with the exception of moving the starter to the other side of the engine and that's not hard. There's lots of info on PFF about this swap. See https://drive.google.com/fi...d3psYzBZR3RncU0/view for What West Coast Fiero recommends to be done and guide yourself from there. A good "how-to" is to be found here: http://fiero34swap.eleventenths.org/

Any used engine you find in a salvage yard is going to be at least 25 years old so you probably will want to have it rebuilt. I'd look at a long block rebuilt engine from Jegs instead. I'm guessing the cost would be close to the same by the time you have it rebuilt (unless you do it yourself) and it would have a warranty. I don't know if there are any performance mods to be made. Others can probably speak to the possibility of a cam, porting the intake / exhaust and 1.6 roller rockers increasing HP and you will probably need 17# fuel injectors.

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Mike in Sydney

pmbrunelle OCT 08, 08:49 AM

quote
Originally posted by Mike in Sydney:
Any used engine you find in a salvage yard is going to be at least 25 years old so you probably will want to have it rebuilt.



And if you're going to be rebuilding (i.e. boring the cylinders for new oversized pistons), then you can look for any GM 3.1 / 3.4 engine, including the aluminium head versions.

If the donor engine comes from a FWD vehicle, the starter is already on the correct side; no drilling needed.

You can dress up a 3.1 / 3.4 as a Fiero, or you can use the aluminium engine's heads, and more of the corresponding hardware. Depends on what you want to do.

An 88 Fiero V6 flywheel (and your chosen transmission) will work with any 3.1 /3.4.
fierofool OCT 08, 09:51 AM
Unless you can get a free one, I would recommend shying away from the front wheel drive 3.1. I found that the 3.1 has no horsepower gain over the 2.8. It's also rated at 140 HP. The only gain is in torque. If you install a 3.1, you can use the Fiero injectors. For a 3.4, you would need to replace the Rochester injectors. I suggest the Bosch injectors recommended in my article in the link below.

I used eleventenths as a basis for my install, but added some information in my install writeup. It can be seen in my second post here: http://www.gafiero.org/bbs/index.php?topic=2080.0

Others added little bits of information, too like the oil pressure sending unit by f85gtron.
Dennis LaGrua OCT 12, 06:53 PM
Early on I tried the 3.4L Camaro/Firebird swap. It wasn't until I rebuilt, changed the cam, ported the heads, the exhaust manifolds and added a turbo that I felt a real difference in . Point is that if you are just looking for a bit more power the 3.4L will provide it but if you are looking for a lot more horsepower, you will need to modify it or consider another engine swap with more potential

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

jjd2296 OCT 12, 07:24 PM
Denis what do you think you were getting in HP after doing all that work and adding a turbo? How much boost were you using in the turbo and what size injectors?
pmbrunelle OCT 12, 08:07 PM

quote
Originally posted by jjd2296:

Denis what do you think you were getting in HP after doing all that work and adding a turbo? How much boost were you using in the turbo and what size injectors?



You want second-hand injectors? Accel 30 lb/hr.
Accel is not considered a good brand, FYI.

I've outgrown them; I replaced them with 42 lb/hr injectors now.

I'm offering them to someone who could use them, otherwise I have no more use for them and in the trash they'll go.

More info to help you decide if my injectors are a good fit for your needs:
30 lb/hr was a good size for my (essentially stock) 3.2 L turbo at 8 psi. Its best 1/4 mile run was 14.122 s @ 97.62 mph. I never measured hp, so I can't tell you how much hp it's making; you'll have to estimate based on the dragstrip stats. More boost psi would need more injector flow; since I wanted to increase boost further, I up-sized to 42 lb/hr.

[This message has been edited by pmbrunelle (edited 10-12-2020).]

Raydar OCT 13, 06:02 PM
Most of us are assuming that you want something that will bolt right in, use the Fiero hardware and computer, and look "stock".
The early 90s iron head 3.1 minivan engines will be the closest thing you will find to a bolt-in, but by now, they are as rare as chicken lips.
As Fierofool mentioned, they have a good bit more torque, but power is kind of a wash.
The 3.4 Camarobird motor is better. Tons of torque, and a bit more power. Moving the starter is the only real "gotcha", but it's been done repeatedly, so it's not that difficult.
(You can get a solid ~200 HP out of a 3.4, without a turbo, but it will be stupidly expensive to do - I had nearly $800 just in my heads.
You will need a cam, ported heads, good headers, free-flowing intake (like Dawg's mod, or a Trueleo) and 19# injectors.
I never had mine dynoed, but it was nearly as quick as my 4.9.)

If you don't care what it looks like, and don't mind doing some re-wiring, the sky is kind of the limit.
Lots of people are doing LX9s, which are aluminum head 3.4s - aka 3400s. Many parts from that generation engine can be mix-matched, and it will bolt in using (mostly) stock Fiero mounts. It will bolt to the Fiero trans, and can use nearly all of the Fiero accessories and brackets.
You will have to cobble together a PCM and harness to run it, but that's also been done to death. There is tons of information out there.
There are also LZ4s and LZ9s, which are "last gen" 3.5s and 3.9s. There is nearly no aftermarket for those, but the LZ9 (3.9) comes with 240 HP, right out of the box, and is almost as easy to bolt in as an LX9. Computer, wiring, exhaust manifolds, and accessory brackets are a whole 'nother story, however.

And there's always the 3800 or 4.9. A bit more complex, but they're out there. But way beyond the scope of your original question.

[This message has been edited by Raydar (edited 10-13-2020).]

CSM842M4 OCT 14, 12:49 PM
Thanks, all. I was sort of leaning towards the early 90's F-body 3.4, partly for the modest power gains but mostly for the ease of installation. The LX9 may become a contender if i ever grow tired of the "S" motor. Next question, in the same vein - anybody running the WCF v-6 headers? Would they fit/work on the S-code 3.4 heads? If so, I may pull the trigger on them to put on the 2.8, assuming the rod bearing swap does what I hope it will...