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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

quote Originally posted by Brian A: Not sure why people are reporting chassis "wiggle" above 350 hp. The good thing about a rear mid-engine car is that, unlike a front engine rear wheel drive car, torque does not need to be transmitted from the front to the rear. The front engine / rear wheel drive configuration requires stiffer and stiffer chassis as engine torque increases. With a rear-mid car, simplistically, all you have to worry about is the engine ripping itself off of the engine mounts.

I think it has more to do with rear toe changes with higher hp/tq engines due to bushing deflection (and why I run rod end lateral links). Could also be chassis rust in the rear frame rails. If you are going to build a high hp/tq Fiero, start with a rust free chassis.

Fiero drivetrains do load the chassis, but differently. The front engine/rear wheel drive chassis sees a rotational force from front to rear due to engine torque x transmission gear ratio. The Fiero chassis sees a bending moment between the rear frame/cradle and the passenger cabin equal to engine torque x transmission gear ratio x final drive. In 1st gear, if there is no wheel spin, this can be in the 4,000 to 5,000 ft-lb range.

This is why engine/transmission mount design on high torque fieros is so important and why Tripots, axles and CVs are prone to break.

quote Originally posted by Josh86gt: Sounds sweet what are you doing about the transmission I'm still trying to figure something out?

Sticking with the F40.

While the F40 is the most expensive manual transmission for a Fiero swap, it is the only one with final drives better suited for high hp/tq applications. My car has the 3.091 final drive swapped in which means 7000 rpm in 1st, 2nd, 3rd and 4th are 44 mph, 82 mph, 126 mph and 176 mph. So it has really long legs which makes the car feel like a late model car with a V8 vs. and over geared hot rod. This also means it pulls down 29 mpg (when it was naturally aspirated) and 27 mpg with the current turbo setup, with a goal of hitting 30 mpg.


It has room for a 9 1/4" twin disk clutch. With organic clutch discs, it has near stock engagement, with a 800 hp rating. Semi-metallic clutch disc material is available to bump the rating over 1000 hp). I swapped out lathes so I had one big enough so I could design and machine the needed flywheel to use this clutch.



It is also the only one with a factory AWD version with 320 hp in a car that weighs over 3500 lbs, with a zero to 60 of 5.6 sec. GM never trusted the F23 to do this under a factory warranty so that speaks volumes in my book. I purchased a CNC mill so I can design and machine the custom center housing for the AWD unit that will allow flipping the output of the AWD unit to the front of the car, and run through a modified oil pan.



You should take some time and review some build threads in the construction zone. Start with the ones that are 15+ pages long and start from the back so you can see where they got to. Once you find and interesting one, start at the beginning and read the whole thing.

quote Originally posted by cartercarbaficionado: i figured put everything awd for the pre 88 minus a bolt in system from a gm that isnt mcpherson. ive been debating on s10 4wd stuff since it should fit

My car is an 88, so the CNC mill was also purchased so I could design and machine new aluminum uprights front and rear to address the wheel bearing/CV reliability issue. The front will get a SAAB factory AWD rear diff installed (flipped over) in the front with a custom tubular cradle and aluminum suspension arms. This will allow the car to be AWD at its current stance.

This year is about optimizing the turbo/ecm/boost/traction control. Next winter will be likely get back to the uprights and move on to the front suspension.

[This message has been edited by fieroguru (edited 02-22-2025).]