I raced a 924 in the early 80's - - I am trying to visualize putting that 4 cylinder front engine/rear drive motor into a transverse mounted Fiero cradle. I think if you go to the trouble of making it a longitudinal motor, using the stock Porsche transaxle, you will gain around 40 horsepower (if memory serves me) The ECM and other considerations will be what will make this difficult.
After investing multiple manhours, and a lot of machining, you will gain a few ponies, but to me a good modified Duke or Super Duty would do a lot more in the way of performance with no more invested, probably much less.
I know the 4.9 V8 would cost much less, for example, as would a Quad 4, even Archies would be competitive in costs.
Frankly, I wouldn't undertake it.
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George Ryan
A pair of 4.9 Cadero's
This '86 SE daily driver:
4.9
5 speed
'88 cradle
Koni's/Eibach/Addco/Prothane
complete Mr. Mikes interior