I don't know if this is a dumb question or not, but will a flywheel from an 84 2.5 work on an 88 2.5? Also are there any differences in the splines on the input shaft from a muncie 4:10 4 spd and a Isuzu 5 spd? I have a junked out 4 cylinder from an 84 all complete with a barely used flywheel and new clutch. Thanks for your input.

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Thank for the sig. Bobadoofunk
1984 White Fiero Sport Coupe (Juliet)
1988 Red Fiero Standard Coupe (bella)
1990 Black Buick Reatta (Noir)
2002 White Chevy Impala base(Haylie)

The spline counts on the clutch are the same no matter what transmission you have, as long as it originally came from a Fiero (all the 4 and six cylinder trannys are the same). The shafts are 1" diameter with 14 splines, (or 1" X 14). I can look up in the parts manual for the interchangeability of the flywheels, but I'd be surprised if they were compatible. The '88 four cylinder engines had internal counter-rotating balance shafts so I'm guessing the flywheel was neutrally balanced. The earlier four cylinders were balanced externally. I'll post the info later today if nobody else beats me to it.

All the 4-cylinders are internally balanced. The balance shafts in 88's are to reduce vertical shake inherent in 4-bangers.
But I don't know if the flywheels are the same. I would think they are, though.