You have just asked the worst question you could possibly ask. On a Fiero related Forum when that question gets asked as Civil War breaks out. Here's a list of engines SWAPPED. 3.4 DOHC, 3800SC series II, 4.6 Northstar, 4.9L V8, 305, 350, 383 Stroker, and even the 400 Small block.
Each person selects the engine they want for their own reasons.With a V8 conversion especially when using the v8Archie kit you retain the stock Fiero Transmission. As well as the adaptors costing around $1,500.
I chose the 3800SC series II for it's ability to rev higher than a V-8 except for the northstar and be able to put out some serious power. You can also use the auto transmission that comes bolted to the engine as well. I like this since the transmission was MADE for this engine.
Want another reason?Watch this.
http://www.fierox.com/speed.movhttp://w ... /race6.mov
Plus the 3800 get good fuel milage too and with a small fuel tanks that's important! Last fillup cost me $9.50 for the cheap stuff. Needle was sitting on E when I got it too. At 1.379 a gallon that's only 6.88 Gallons that it took in. I believe I have a 10 gallon tank.