Advice needed on an Engine/Transmission swap. (Page 1/5)
Murcie-Me JAN 27, 12:02 AM
Hello forum, my name is Michael and am new to this forum. I have been on other forums for many years (Mad Mechanics, Lamboclone, Kitcarhub) and have built many Lamborghini replicas using Fiero's as a base.
I built my (Murcielago) more than 14 years ago and it is still the most advanced replica to date. I have always loved Fieros. but back when they were in production I was just a poor college student and could never afford one.
I have always said I would NEVER do an engine swap in my build (86 SE 2.8L AT) unless I could do a swap that would make it sound more exotic. Without spending a fortune I know that will never happen, and I'm ok with it.
I would like to do a swap now though, and I need your advice on a few things. I'm thinking of going with an LZ9 engine from an '06 pontiac G6 or Chevrolet Impala. I see most people recommend using the Microsquirt engine management unless someone can point me to a better option.
Here are my questions:
1) will the LZ9 bolt up to my TH125, and will it handle the additional power (240HP)
2) Should i swap out the TH125 for a 4T60, and if so will my existing axels from the TH125 plug into the 4T60?
3) Will the Microsquirt also control the lockup function on the converter clutch?
4) If I go with a 4T65E instead (more readily available), what compatibility problems will I face?
I have a thousand more questions, but these are the ones I can't seem to find any info on.
I'm sorry if I posted this in the wrong topic, but i'm not sure where to post it. I realize there are many threads on engine swaps with 3800 and 3400 engines, but I can seem to find any of these questions addressed and advised.
Thank you in advance for any help you guys can offer.
1985 Fiero GT JAN 27, 02:21 AM
I'm doing a 3400 turbo with f23 5 speed manual trans, with mega squirt 3 pro mini ECM, I wouldn't get micro squirt unless you only want very basic stuff, the 3 pro mini is not nearly as expensive as a full mega squirt, but has much more functionality than the micro squirt. These do not come pre programmed, however the basic get it running info is easy enough, download app, plug it into computer, enter engine parameters (size, cylinder numbers, firing order, ignition system type, what sensors are hooked up to what wires, etc.), and it will have basic example tables that can be changed to get what you need.

Micro squirt will be no easier to tune, and you can't run sequential fuel injection (each injector firing one at a time, in time with its cylinder) only batch/bank fire (all at same time, or each "bank" of 3 together), which makes it drive better at low rpms, but no effect on high rpms. Also more flexibility on the io with the mega squirt 3 pro mini.

(Disclaimer: I have not yet even installed my mega squirt, just played around in the software, and seen what other people say and do, it is going to be a lot of fiddling with numbers until it "feels" right, but there are instruction manuals for each of the ECU products, they describe things well, and seeing what other people have done makes everything easy enough to understand)
Murcie-Me JAN 27, 03:08 AM
Thank you for that info! I think I would want the sequential firing as opposed to the bank firing as long as its possible on the LZ9 engine. I will be doing the cam swap to eliminate the VVT, seems like it would be better that way.
So now I have to figure out the compatibility issues as far as mating the new LZ9 to the existing TH125. I feel the existing trans will handle the added H.P (somebody correct me if i'm wrong), and it would eliminate the possibility of having to have new axels made if I have to upgrade to a 4T60 (non "E") transmission. The reason I would go with the non-E version of the trans is because the only electric connection to it would be the TCC, the TV cable would control the shift timing just like the TH125. I could be wrong about that also, maybe the mega squirt can control the shift points of the 4T60"E" as well?
Like I said, this is all new to me and I am grateful for any insight and advice you guys can offer.
82-T/A [At Work] JAN 27, 07:39 AM
Are you telling me that the car in those pictures is a Fiero? That's amazing... the fit and finish is spectacular on that car! I've not spent a whole lot of time looking at that model, but I think unless I owned one, I would never be able to tell the difference. I've seen some pretty decent Fiero kit cars (looking like Ferraris or Lambos), and this is definitely right up there at the top. I am very impressed.


As for the swap, I'd basically echo everything that 1985 Fiero GT said about going with the 3400 series motor, of which the LZ9 is a member of. I'd personally shy away from the LZ9 simply because the VVT makes it a bit more complicated, and likely means you'd need to re-use the factory ECM. I'd probably go with the 3500 motor (the LZ4). These motors are AWESOME... they are also all 60 degree, which is considered to be a very optimal design for high-revving engines, even if GM didn't fully take advantage of it. You're not going to get insane / sick power from the LZ4 in a Fiero... but I don't think 260hp is unreasonable (with a LZ4) with a shorter exhaust, shorty headers, and using a much more direct cold-air intake that the Fiero has. Plus some mild port-matching. Here's a nice article on the LZ9 and LZ4: https://www.autoweek.com/ca...240-horse-cimarrons/

These engines won't have the V10 sound you're looking for... but they definitely sound really nice at higher RPMs.

I would also definitely get rid of the Th-125. It was a nice transmission for the time, but it does not do the engine justice, and isn't great on the highway if you want to cruise. I would go with either a 4T60 or 4T65E. You can purchase separate controllers for both of them from Summit Racing. Here's a great article from Sinister Performance on the transmission models: http://www.gmtuners.com/tech/440_4T60E_4T65E.htm


One other thing I want to mention... these engines were designed as Sequential-port Fuel Injection motors (SFI), as compared to our stock V6 motors, which are Multi-Port Fuel Injection. The difference of course is that SFI fires the injector for each specific cyl (just before valve opening), where as the MPFI motors dump fuel in a batch... meaning three injectors fire and the fuel may pool at the top of the valve while it's closed for half a second (or whatever it is). SFI is significantly more efficient than MPFI... and I recommend keeping SFI if you can.

At wide open throttle, there is essentially no difference because the valves are opening and closing so fast that it really doesn't make any perceivable difference. But in the lower RPMs (EDIT: lower to mid-rpms), SFI really shines. You'll get better low-end performance and around-town driving with SFI than you will with MPFI. Keep in mind, all of these engines switched to SFI back in 1993... so they were all designed with SFI in mind, and are rated based on an SFI configuration. It makes the car a better-driving car in around-town driving, and makes it a bit more responsive. You also get better fuel economy and emissions for whatever that's worth.

There are a couple of aftermarket systems that support SFI, but if you're going to go with the Microsquirt/Megasquirt, you'll want to go with the MegaSquirt 3 Pro... as it's one of the only ones that supports SFI.

[This message has been edited by 82-T/A [At Work] (edited 01-27-2025).]

1985 Fiero GT JAN 27, 10:31 AM

quote
Originally posted by 82-T/A [At Work]:

There are a couple of aftermarket systems that support SFI, but if you're going to go with the Microsquirt/Megasquirt, you'll want to go with the MegaSquirt 3 Pro... as it's one of the only ones that supports SFI.




Yeah micro squirt only has 2 injector outputs, but it does cost $300, the mega squirt 3 pro mini has 8 injector outputs (the 2 unused ones can be used for anything, turbo wastegate control, air conditioning, TCC lockup, etc.), it costs $600:
https://www.diyautotune.com/product/ms3pro-mini
It also claims vvt control, so you should look into what that would require, and how that would work in your specific application. One thing to make sure of, this ECM will only work with PWM IAC valves, I don't know what the lz9 has, but if it is a 4 wire stepper motor (like Fiero) then you'll have to get it working with a seperate PWM IAC valve.
Murcie-Me JAN 27, 01:01 PM

quote
Originally posted by 82-T/A [At Work]:

Are you telling me that the car in those pictures is a Fiero? That's amazing... the fit and finish is spectacular on that car! I've not spent a whole lot of time looking at that model, but I think unless I owned one, I would never be able to tell the difference. I've seen some pretty decent Fiero kit cars (looking like Ferraris or Lambos), and this is definitely right up there at the top. I am very impressed.





Thank you 82-T/A, yes its actually an '86 SE Fiero. The entire Fiero body was removed, the chassis was stretched at the engine cradle mounts, and then a new body frame applied to mount all the panels to. I was a lot of work, took me 14 months and $38k from start to finish.

Yes the LZ9 is a VVT engine, but that can be eliminated with a different cam which I intend to do.
Do you know if the 4T60 trans is the same size as the TH125? When I did the Lamborghini build I put wide track suspension on the car, which meant I had to have custom HD axels built to be longer and adapt the TH125 to corvette C4 hubs. Since it was $1200 for the pair, i'd like to not have to do that again. If the 4T60 is the same dimension as the 125 and accepts the same CV joints it'll save a lot of headaches and money.

So when the mega is installed, do I no longer need the original ECU from the Fiero?
From what i've read in other articles, it doesn't seem to be a big deal to wire the mega squirt to the engine, but do I have to make my own harness?
82-T/A [At Work] JAN 27, 01:28 PM

quote
Originally posted by Murcie-Me:
Thank you 82-T/A, yes its actually an '86 SE Fiero. The entire Fiero body was removed, the chassis was stretched at the engine cradle mounts, and then a new body frame applied to mount all the panels to. I was a lot of work, took me 14 months and $38k from start to finish.

Yes the LZ9 is a VVT engine, but that can be eliminated with a different cam which I intend to do.
Do you know if the 4T60 trans is the same size as the TH125? When I did the Lamborghini build I put wide track suspension on the car, which meant I had to have custom HD axels built to be longer and adapt the TH125 to corvette C4 hubs. Since it was $1200 for the pair, i'd like to not have to do that again. If the 4T60 is the same dimension as the 125 and accepts the same CV joints it'll save a lot of headaches and money.



So, the swap is easy, and the 4T60 will mate up directly to the engine no problem... it's the same bell housing. Here's an article (I stole from someone else) and posted on my old website from the 90s: https://www.pontiacperforma...es/4_Speed_Swap.html


Here's the part about the axles though, which is less than ideal:

"The stock Fiero axles cannot be used with the four speed automatic. For a 4T60 you can use right and left axle assemblies for a '89 Pontiac 6000 with 4T60 and light duty brakes. The correct part numbers are A1 Cardone P/Ns are 60-1115 and 60-1078 or CCT 8471 left and 8430 right."

Also... the stuff in the link above about notching the subframe, that's ONLY if you have an 88... you won't have to worry about any of that.

But yeah, looks like you'll need new axles.



quote
Originally posted by Murcie-Me:
So when the mega is installed, do I no longer need the original ECU from the Fiero?
From what i've read in other articles, it doesn't seem to be a big deal to wire the mega squirt to the engine, but do I have to make my own harness?



No, if you install a MegaSquirt or something else... you basically replace the Fiero's factory ECU. You would have to make your own harness, but honestly... I'll tell you, it's really not that hard. Just make the harness with the engine sitting on the cradle OUT of the car, or on the engine stand. You don't want to have to build it with the engine already in the car. But it's not hard at all. I remade one for my daughter's 85 Fiero 2m4 SE, and it went perfectly except I managed to screw up the wires leading to the temperature gauge, haha... everything else is great.

There are plenty of options outside of the Mega/Micro Squirt too... just depends on what you want to use. Some of them are self-learning, like the Fast EZ-EFI 2.0, etc. But go with what you think has the best support for the motor (as in... what other people have already used, that you're also looking to do).
1985 Fiero GT JAN 27, 01:33 PM

quote
Originally posted by Murcie-Me:


So when the mega is installed, do I no longer need the original ECU from the Fiero?
From what i've read in other articles, it doesn't seem to be a big deal to wire the mega squirt to the engine, but do I have to make my own harness?



Yeah, try to get the harness (or at least all of the electrical connectors on each sensor etc.) with the new engine, get the 8ft flying lead harness with the mega squirt, then splice all 3 together, using the connector ends/pigtails from the new engine, the body wiring (VSS, reverse switch, things like that) from the Fiero harness, and the majority of the wiring will be from the mega squirt harness, which is just a bunch of 8ft cables, route everything as nice as you can/want, and that should be it.
Dennis LaGrua JAN 27, 02:54 PM
Nice job on the kit car. It sounds as though you're on your way to a very very nice engine swap. Good choice as the LZ9 is the most powerful of the high value GM engine family. An aftermarket cam cam will eliminate the VVT and can significantly boost horsepower. IIRC the engine weight will be close to the 2.8L V6. While the 4T60 4T60E and 4T65E HD will bolt up to the LZ9, The strongest easiest to fit transmission would be the 4T65eHD. If you use that box you will need an independent transmission controller.
A number of LZ9 3900 swaps have been done and there is a ton of info out there.

------------------
" 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 "

[This message has been edited by Dennis LaGrua (edited 01-28-2025).]

Murcie-Me JAN 27, 04:51 PM
Thank you Dennis, it was definitely a labor of love build, something I can hang onto and pass down to my kids.
I do Special Effects and props for the studios here in southern California, and everything I build eventually gets thrown in the trash after its shot, or disassembled for the parts. It was nice to build something knowing it won't be discarded in a few months lol.
Correct me if I'm wrong, but the 4T60 (non "E") is basically a 4 speed TH125 (stronger though) and the only electrical would be the TCC control. Shift timing is provided by the TV cable (like the TH125). Is it possible to control the TCC with the megasquirt, or would i need a separate control unit to plug into the megasquirt? What else would be required in order to electronically control the shift points on the "E" transmissions?
I'm not opposed to using the 4T60E or the 4T65E, I just don't know what all would be necessary to control the electronic requirements of those transmissions.
My donor car will most likely be a 2006 Chevrolet Impala, they have the LZ9 and a 4T65EHD transmission.