Ecotec turbo swap transmission options question (Page 1/4)
SteveMushynsky NOV 16, 07:16 PM
Thanks to all here for the learned advices offered.

Regarding a swap of a turbo Ecotec into a Fiero, I am looking at a transmission choice between F35 or an F40 options.

This will be a daily driver vehicle with an occasional heavy foot applied. No racing, etc so I don't anticipate beating the tranny up. The LHU and LTG engines (stock) produce up to 270 hp and up to 295 ft-lb torque, hence my focus on an F35 or F40. The F35 is rated to at least 260 lb-ft input torque. The F40 is rated to at least 295 lb-ft input torque. The Fiero being lighter than the vehicles these are usually found in, I'm sure these would be my optimal choices for an Ecotec/Fiero swap.

I've read much about required intermediate shaft and axles requirements. My problem at hand is which one would be the least difficulty / least expensive choice, with least expensive being my primary concern.

Which transmission would you advise I choose to use with a turbo Ecotec, an F35 or an F40, and why?
What, exactly would one need to accomplish installation (flywheel, clutch, half shaft, axles)?

Thanks in advance for any help with this.


------------------
Steve Mushynsky

1984 Fiero 2M4
34K miles

1986 Fiero SE I4 (donor now)
Lots of good miles. One very bad mile.

1987 Fiero
Tried to kill me (gone to a 'better place')
Prior owner failed to tighten a bolt. Trailing arm separated at 70 mph

[This message has been edited by SteveMushynsky (edited 11-16-2019).]

oldrock2401 NOV 16, 08:37 PM
A lot of the ss/redline guys prefer the base model f23 to the sc/tc f35. F23 are dime a dozen and have been said to be stronger than the f35. Besides that information, I'm not too much help to ya. I would go with whatever has a better gear ratio for your planned application.
SteveMushynsky NOV 16, 09:15 PM

quote
Originally posted by oldrock2401:
A lot of the ss/redline guys prefer the base model f23 to the sc/tc f35. F23 are dime a dozen and have been said to be stronger than the f35. Besides that information, I'm not too much help to ya. I would go with whatever has a better gear ratio for your planned application.



Thanks for the reply, oldrock2401.

The F23 is rated by GM for at least 170 lb-ft torque. With the LHU and LTG producing up to 295 lb-ft torque, the F23 looks to me to be inviting eventual problems.

There are F35s available with limited slip differential and 4.05 final drive ratio for $500 and up, though their mileage is high. F40s with 3.76 final drive ratio can be had for $250 and up with half the mileage. Either can be had in Ecotec bellhousing versions.

So, my personal choice is F35 or F40. What's needed re half shaft, axles, etc and costs thereof is the question.

------------------
Steve Mushynsky

1984 Fiero 2M4
34K miles

1986 Fiero SE I4 (donor now)
Lots of good miles. One very bad mile.

1987 Fiero
Tried to kill me (gone to a 'better place')
Prior owner failed to tighten a bolt. Trailing arm separated at 70 mph

oldrock2401 NOV 16, 10:34 PM
Im aware the f35 is "rated" higher, hop on the ss forums and many switch to the f23 because its stronger, theres quite a few guys with 500+whp on them in both that community and the 3.8 community here. Just because paper says its better, doesn't mean it is. F35 has different axles than the f23. There's quite a bit of information on here that covers f23 stuff for our cars, which is why I brought it to light.
SteveMushynsky NOV 17, 02:09 AM

quote
Originally posted by oldrock2401:
I'm aware the f35 is "rated" higher, hop on the SS forums and many switch to the F23 because its stronger, There's quite a few guys with 500+ whp on them in both that community and the 3.8 community here. Just because paper says its better, doesn't mean it is. F35 has different axles than the f23. There's quite a bit of information on here that covers f23 stuff for our cars, which is why I brought it to light.



Your reply is why I posted my intentions: To learn and to steer me toward info sources I should become familiar with. I've done a lot of reading research on the F23 and other options here and elsewhere. I'm fully aware that reading and studying isn't the same as experience. Questions, though, on how the F23 has been able to amass such a reputation despite GM's engineering criteria. Having some engineering background myself, I do know that breaking/shearing strength is one thing, but wear resistance and reliable lifetime is another. Loyalty to a well-established and widely used technology is no doubt another factor (ie: the 3800 Buick V6 engine's very strong following).

The F23 popularly swapped into the Fiero came in earlier vehicles with non-Ecotec engines. It is a logical replacement for the earlier Getrag in many Fieros.
The F25 and the F35 were used in vehicles with the supercharged and early turbocharged Ecotec engines. The F40 was used in later cars with the higher output LHU tubo'd Ecotec.

A 500 hp vehicle equipped with an F23 would appear illogical, unless longevity was not a priority. It would be for me, though. I would guess that a 500 hp Fiero would likely be built and used occasionally as a race car and not for multi-year, high mileage daily driver use, where wear and reliability are big factors.

As a general rule, I am inclined to use as-current technology as feasible and that I can afford and that is engineer-designed to accommodate the application I would use it with. Yes, I fully acknowledge that builders of what are or essentially are high-performance race cars can accomplish amazing results outside the normal performance envelope, but that's not me. There's too much the practical engineer in me.

So, I think I'll stay with my chosen options being an F35 or F40. What are the issues of installing either of these?

------------------
Steve Mushynsky

1984 Fiero 2M4
34K miles

1986 Fiero SE I4 (donor now)
Lots of good miles. One very bad mile.

1987 Fiero
Tried to kill me (gone to a 'better place')
Prior owner failed to tighten a bolt. Trailing arm separated at 70 mph

wftb NOV 17, 04:31 AM
You need the F35 from the lsj supercharged cobalt as. The later turbocharged f35 transmision’s axles will not fit Fiero hubs. The F23 takes Fiero axles making it much easier to source. The f40 also needs axles from the supercharged cobalt SS

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86 GT built 2.2 ecotec turbo
rear SLA suspension
QA1 coilovers on tube arms

SteveMushynsky NOV 17, 06:57 AM

quote
Originally posted by wftb:
You need the F35 from the lsj supercharged cobalt as. The later turbocharged f35 transmision’s axles will not fit Fiero hubs. The F23 takes Fiero axles making it much easier to source. The f40 also needs axles from the supercharged cobalt SS



Thanks for your reply, wftb. I had repeatedly read that the outer end of Cobalt axles will not fit the Fiero hubs, but unsure what year Cobalts equipped with what transmissions they were writing about.

Is it accurate that the axles from the earlier supercharged Ecotec Cobalts equipped with the F25 transmissions WILL work with an F35 transmission and mate with Fiero hubs, but that the axles that were used in the later F35-equipped, turbocharged Ecotec Cobalts will NOT fit Fiero hubs?

In other words, one can use an F35 transmission off a later year turbocharged Cobalt in a Fiero IF one replaces the later year turbo Cobalt axles with the earlier year supercharged Cobalt axles, correct?

Is it safe to assume that the later year Cobalt's transmission jackshaft can be used with the earlier Cobalt axles?

Will the resulting axles & jackshaft lengths be correct without modifications?
Are the earlier axles strong enough?

If I can definitely resolve this, I will feel much better about the feasibility of this project for me.

I will be using the F35 as it is lighter and smaller than the F40. The final drive ratios are close to each other as is the span of ratios from lowest to highest gears. The input torque rating of the F35 is a bit lower than I would like for an LHU or a LTG engine, but I'm sure that its engineered safety margin and my not hugely heavy accelerator foot will make this not a problem for me. I don't think I would care for cramming the offset Ecotec + big F40 combination into the Fiero cradle.

Hopefully this will put my axles worries to bed. Now I can constructively worry about something else.

------------------
Steve Mushynsky

1984 Fiero 2M4
34K miles

1986 Fiero SE I4 (donor now)
Lots of good miles. One very bad mile.

1987 Fiero
Tried to kill me (gone to a 'better place')
Prior owner failed to tighten a bolt. Trailing arm separated at 70 mph

SteveMushynsky NOV 17, 07:54 PM
More info found from this thread:
F23, F35, F40 Transaxle inq!!! by 4thfiero
Found at:
http://www.fiero.nl/forum/Forum2/HTML/132232.html
(Quotes are excepted from the original)

4thfiero: "F23 M86: Will this tranny accept Fiero axles? Will the stock cobalt axles fit the Fiero hubs? Will one of those jack shafts (or half shafts) fit into the f23 and will a Fiero axle fit into the jack shaft?
Same questions for the F35 and F40 trannys... I really wanna use the F23 tranny with the jack shaft and 2 drivers side Fiero axles...will that work? If not, what can i do to make it work...(like using Cobalt axles if they are compatible)"
Also... Can I hook up a 5 speed Getrag shifter (inside the car) to a 6 speed F40????
Will that "transform" my 5 speed shifter into a 6 speed?
I would LIKE to use the F35 or the f40 tranny with my 2.4 turbo set up. I just need to know about the shifter and the axles...Do I use cobalt axles? Of what year? Which jack shaft do I use as well... I need a parts list to make this work and have everything the length I need!"

fieroguru: "One of the primary reasons people pick the F23 is because stock Fiero axles are used with it.
The F40 and F35 can both use the Cobalt SS (supercharged version, not the turbo version) axles and intermediate shaft when installed in a Fiero. The F35 would place the engine in the approximate stock location, the F40 would shift it 1" to the passenger side (which there might not be room for - like many of the V8's).
For the F23 or F35, you can use any shifter you want as the reverse lockout is part of the transmission. On the F40, its not part of the transmission and the Fiero 4 speed shifter is needed since it has the reverse lockout built into it."

4thfiero: "So if I'm reading this correct...
I can use the F40 with cobalt supercharged axles and jack shaft...but the 5 speed shifter won't work with the 6 speed, but the 4 speed shifter will!
If I use the F35, again use cobalt axles and jack shaft...and can I use my 5 speed shifter just fine?"

fieroguru: "Correct. The engine placement of the F35 will be very similar to a stock Fiero, but the F40 will need it to be 1" further to the passenger side and some engines don't have the room on the passenger side for this shift (mostly the V8's).
The F23 and F35 can use a Fiero thickness flywheel (about .82"), but the F40 needs one that is much thicker.
4 speed shifter when used with the F40 needs to be modified (expand the slots to allow the 4th shift gate and to relocate one of the cable brackets on it).
Custom shift cable brackets will be needed on the transmission side for any of the 3 transmissions and the needed shifter cables depends on your cable bracket design. If you use 2 Getrag select cables, you will likely break the one used for shifting - It simply isn't large enough for aggressive shifting.
Custom transmission mounts are also needed for any of the 3 transmissions."

4thfiero: "Does the 5 speed Getrag shifter need to be modified for the f35? And do you know what cables I would need?"

fieroguru: "If you want to run the F40 with 2 Getrag select cables, then yes, the 4 speed shifter must be modified. The modification involved opening up a slot and relocating a shift cable bracket (cutting/welding)."

------------------
Steve Mushynsky

1984 Fiero 2M4
34K miles

1986 Fiero SE I4 (donor now)
Lots of good miles. One very bad mile.

1987 Fiero
Tried to kill me (gone to a 'better place')
Prior owner failed to tighten a bolt. Trailing arm separated at 70 mph

fieroguru NOV 17, 09:24 PM
That thread is 5 years old. There is now a better cable combination for the F40 and you can now use a 5 speed shifter with it with a bolt on reverse lockout.

The current issue is most available parts for the F40 are for the G6 version. The ecotec version is different in bolt patterns for mounts, clutch line connector, and shifter assembly mounting flange.

The F35 isn't any better... I think it has been used in a Fiero 1 or 2 times, so there isn't a kit for it either.

SteveMushynsky NOV 18, 03:04 AM

quote
Originally posted by fieroguru:
That thread is 5 years old....



Thank you again, fieroguru. I was hoping for updated comments.

The F40 looked like more size, weight, capacity, complexity and expenses than I wanted for this project.

The F35, I hoped, was going to be less complex / less costly regarding the axles aspect. I am comfortable with the above info resolution of that.

I had seen the bolt-on reverse lockout item online and am holding that thought in reserve in case I need it. My swap car currently is equipped with the early '84 4-speed transmission and associated gear. My donor has a THM-125 automatic.

As to linkages, etc needed to install an F35, that's my next focus of research. I believe I've seen a build thread or two that were to use an F35, although I don't remember if they got that far. We also have a SAAB parts yard near me for stuff & inspiration. Any info or leads to same on this aspect of installing an F35 in a Fiero would be welcome.

I have time to figure this all out, as I have yet to strip my red 1986 Fiero SE I4 donor car after clearing my garage to store parts. That will be my primary concern for the rest of this year, as my darling spouse has once again threatened to have it dragged to our corner and decorate it with lights for Christmas.

When I have the poor thing stripped, I will be listing / have available a passel of parts for purchase.

------------------
Steve Mushynsky

1984 Fiero 2M4
34K miles

1986 Fiero SE I4 (donor now)
Lots of good miles. One very bad mile.

1987 Fiero
Tried to kill me (gone to a 'better place')
Prior owner failed to tighten a bolt. Trailing arm separated at 70 mph