This is maybe a ridiculous idea, but has anyone tried stuffing a big block Olds x TH375 in a Fiero?

I'm aware of the LS4 x FWD trans swaps out there, and wondered if dimensionally, the BBO x TH375 would even fit.

I'm guessing there is no tilt in the BBO relative to vertical to allow it to fit.

Anybody think of doing this too?

That trans has been used as well as the TH475 (4 speed). The one's that I have seen use a SBC and the entire powertrain is longitudinally mounted. The entire trunk must be cut out which leaves questions on frame strength without sufficient bracing for the strut towers. its a tight fit, difficult install and a very heavy one. Part of the SBC oil pan must be cut away for the axle to clear. That decreases oil capacity. IMO this is not the type of swap that makes sense in a Fiero. If you want V8 power the LS4 seems like the best choice, followed by the lightweight Cadillac's 4.5L/4.9L and later Northstar's.

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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 "

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My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

I saw that Fiero many years ago and the supercharger snout extended into the passenger compartment and sat just inches from the drivers head. There was no steel fire wall separating the engine from the passenger compartment . The only "protection" (if you want to call it that) from the rotating members, belt, loose parts, or from a potential engine fire was a thin clear plastic shield. There are so many rules violations set by NHRA in this build that no track would allow this Fiero to race. Except for show, there is little purpose to this build.

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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 "

The V8 swap with the 425 and 375 has been done quite a bit over the years. Search for longitudinal fiero and you will find lots of pictures and information on the swap.