Calling Detroitish swapped Fieros (Page 1/1)
pHoOl JAN 25, 06:33 PM
Hi all,

I've been on here a while (mostly lurking) and I'm on my 3rd Fiero. I've always wanted a swapped one, but currently driving a kinda low mile 86GT. I'm approaching mid life crisis age and think I need to start planning, so I'm starting to research various swap choices. My money no object swap would probably be an LS4, but i highly question my skills in convincing my lovely finance department.

I'm looking at the 4.9, 3800SC or turbo, and a turbo ecotec. I'd like to see if there's somebody in the metro area that'd be willing to let me take a look and maybe take me for a spin around the block to check them out when the weather gets nice and the salt is gone. I'm planning on going to the 40th, so I'm sure I'll be talking to owners there if I can find them.

I'm over in Novi, but I'm up for a cruise pretty much anywhere an hour or so away.

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86 Fiero GT

cam-a-lot JAN 25, 10:57 PM
Get a hold of olejodad on the forum. One of the most knowledgeable people around- he can guide you in the right direction
zkhennings JAN 26, 12:13 PM
I will say I do not have much experience with the 4.9, but I think power potential is not the greatest, and working on a V8 Fiero is always harder than a V6 or I4. I did heavily consider both a 3800 and an ecotec swap.

Ecotec benefits are an overall lighter package, and easy to work on everything since the motor is so small. Cons are it is more expensive because you will probably have to build the bottom end a bit to make near 3800 with a pulley power, you will have to get a different trans, though I think if you get an ecotec pattern F23 you can use the stock axles no problem. You will have to do a lot of fab for motor and trans mounts and for the shifter mechanism, I have yet to see an ecotec swap that did not require lots of cradle mods.

3800 will be cheap and easy, it is well documented, motors are dirt cheap, ECU is easily hacked and you can get a tune for cheap, they only need a pulley and tune to make 300hp. It bolts up to a getrag, mounting solutions are simple and purchasable. You can even buy a wiring harness for it. The stock bottom end can pretty much hold all the power you would ever want for it. The only downsides are weight and a V6 is harder to work on than an I4 in the engine bay. It is certainly the path of least resistance, with the most power potential, the most documentation, and the least expense.

The most NA power per weight at a cheap cost is probably a 3900, that's what I am doing. It requires more fab than 3800, but less than ecotec. Could do LFX (DOHC 3.6) but it is more expensive, requires a bunch of fab, and impossible to work on in the engine bay. I wanted the physically smallest motor with the most NA power potential, and I think 3900 is it. I expect to make 300hp NA, and it weighs less than a 2.8. It is kind of a baby LS motor, very similar designs in some aspects. They also love boost if I ever want to go that route. Issues with putting it in a Fiero are alternator location, water fill location, and oil filter location. The AC compressor may foul the hump in the stock crossmember. You can use an 88 front mount for it though, and it bolts up to stock trans with stock 88 flywheel and clutch. But overall only a little more work than a 3800 and it is probably close to 100# lighter. In NA form probably only slightly heavier than or equal to an ecotec with full turbo setup. And in NA form, it is probably easier to work on than a turbo ecotec. You can use a factory computer and splice wiring harnesses, I am going with Megasquirt though.

So it depends on your goals, if you are happy with 250hp 250ftlbs, then its a great candidate to swap in stock with a stock ecu. If you want 350+, then 3800 will be the cheaper way to get there. If you want 400+, then both a 3800 or 3900 will need a turbo setup and they are probably very close in effort, and I would consider either. I would say both motors can hold 500hp on a stock motor pretty comfortably. Ecotec turbo is cool too for that 350-450hp range, but it will need bottom end work, and way way more fab work in the swap will be necessary. But it will be the lightest package once you are hunting for those hp ranges, followed by 3900, and then 3800 being the heaviest.

[This message has been edited by zkhennings (edited 01-26-2023).]

MichiganReefer JAN 26, 09:24 PM
I am in the Detroit area, car is garaged in Plymouth. Going through a 3800 L67 and 4t65e-hd swap now, my first project car. I'm hoping to have it started/put together before the end of spring, but as of now it's still mostly apart. Once it's running I'll have it in Detroit proper. I've been asking questions and have gotten help from olejoedad, he's been amazingly helpful and has done Fiero work for years. He's currently doing my electrical harness work. Reach out to me if you have some questions of engine/transmission work or general swap information. Once I get it running I'd be happy to give out a ride, but it's not ready.
pHoOl JAN 27, 12:40 AM
@michiganreefer, thanks! I'll definitely take you up on that when you're ready. Good luck on it, but like you say, the 3800 is a well sorted swap that's been document on here. Hopefully you're not finding a shortfall of info.

I definitely have olejoedad and his son in mind... I reached out to him shortly before posting this. I can't say i've heard a negative thing said about either of them, so unless my PMs start blowing up with haters, they'd be high on the list if I end up going forward with something.

@zkhennings, I hadn't thought of the 3900, though that is an interesting alternative. Power level would be near what I was looking for, and it came with the F40 manual. Hmm... might have to ponder that more. 60* v6, so likely wouldn't sound any better or worse than the 2.8. Might even be able to run regular fuel too.

Not sure I'd look to build into the 400s... 250-350 would probably be plenty. I never got bored of the Ion Redline in my signature, had it 9 years before I sold it. That was 205hp with the blower. Which, one often argument I've seen on here against the 4.9 was that it's <i>only</i> 200hp... but with 275 torque I'm sure it feels a lot faster than 200hp. (Side note, I realized how long it's been since I posted since I haven't owned any of those 3 cars in a very long time)

One question I have on the 3800... I've got the 4sp muncie, which I believe is one of the stronger manuals, at least as far as stock Fiero trans come. Would that be a decent choice in terms of gear ratios, highway RPM, etc for the 3800?
mafv8 JAN 28, 06:21 PM
You did not mention a SBC swap, but if you were interested thats what I have, lots of options for tuning, I have 320ish hp. And I live in Northville, although hiding from the snow in Arizona currently. I will be back in mid-april if you wanted to come and see.

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84SE, aero body, 4 speed and an injected 355 V8

zkhennings JAN 29, 08:18 PM
The 3900 sounds really good, better than the 2.8. Kinda sounds like a 60* Nissan VQ v6. With a good exhaust it can sound pretty exotic. There’s an lz9 fiero on youtube that sounds really good, username “Phantom Formula”. Stock headers with a custom Y pipe and exhaust.

In regards to the 4 speed, it should hold the power fine, probably might eventually get sick of it on the highway, but you could swap in an f23 at that point.

[This message has been edited by zkhennings (edited 01-29-2023).]

pHoOl JAN 30, 10:11 PM
@mafv8 I'd definitely love to check out your SBC. I'm in Novi, so you're practically next door.

zkhennings, I checked out that guys clips on youtube... dang, sure does sound good. One other thing I've been thinking about, mentioning that I'm at less than 100K miles is that I wouldn't really want to swap with a motor that has higher mileage than what I've got. To that end, I browsed real quick this evening and found two examples within a few hours drive from me of 3900s for sale. One with 40k miles, one that was a dropout with only 14 actual miles on it. Certainly seems to have some things going for it. Not to mention, being the engine is 15 years old as opposed to 20 or 30... just thinking about parts availability 5-10 years from now.


I spent some time on youtube, only found a few people that seemed to have the 3900. But were they saying the engine and trans use the existing 2.8 mounting points? IE, wouldn't need specially fabricated mounting brackets? I think they mentioned the oil filter seems to be in an awkward spot, and I thought something else that might have to be moved. But I figure a remote oil kit could probably be had.

Very interesting indeed. Hopefully if it's an easier swap requiring less custom fabrication, that'd help to lower the overall cost to swap.
zkhennings JAN 31, 02:48 PM
You can use an 88 motor mount and bracket with it yes, but there may need to be some clearance to the front crossmember required due to the hump in it where the stock exhaust runs possibly interfering with the AC compressor.

If you get a 3900 out of a Buick Lucerne, the alternator ends up against the firewall of the Fiero and just requires some trimming of one of the hinge boxes. You can also buy any 3900 and get just the coolant crossover for the Lucernce and slap that on and same thing.

It is slightly more complicated than a 3800 swap, but it has a lot of benefits, the heads flow amazingly well and are aluminum for weight reduction, no balance shafts necessary, uses a stock 88 flywheel with no machining required and will mate to a Fiero trans no problem, super light starter motor, forged stock crank, super good oiling system with a MASSIVE oil pump, oil squirters in every single cylinder, a super trick coolant crossover system that circulates coolant around the motor to homogenize temperatures, and that has the side benefit of greatly lowering water pump load for less parasitic horsepower loss. It is a lot of LS engine tech carried over.

It also fits LS1 valve springs, keepers, and retainers, and it has LS style lightweight cast rocker arms (they are not the same dimensions).

Bosch EV14 fuel injectors for an Audi 2.7 fit the stock fuel rail without modification, I think there are Siemens injectors that fit it as well.

There is no return line on the fuel rail but you can use a corvette fuel filter that has the regulator built in and returns extra fuel to the tank so it is a very easy problem to solve.


The 3800 is a much older engine lacking a lot of the tech of the 3900, but it is a tank at the expense of weight. I think the 3800 is around 460lbs and the 3900 is around 360lbs. They are both tanks though, there have been a couple bone stock 3900s that have been turbo'd and made over 500hp, and one of them is in a 10 second Camaro owned by MARS on the 60*V6 forum, and he has made 100s of passes without issue.

If more people started swapping them, 3800 swaps would probably start losing popularity.

[This message has been edited by zkhennings (edited 01-31-2023).]