Still trying to make a descision.

I'm leaning more and more towards rebuilding the four cylinder engine, the twisted logic behind this is the money I would have to spend on a bigger turbo and time and materials to mount it on the 3400 should be nearly equal to the four connecting rods and four pistons I would need to make the four cyl work. The factory exhaust manifold for the 3400 might work, they are cast iron, but the crossover is regular pipe and has a flex piece in it and I don't think that would be good for the turbo, maybe I'm wrong, don't really want to be wrong and have something melt down or break. So I'm planning on using Eagle 6.25 inch long, small journal Chevy rods part number CRS6250SLW, they are H-beam con rods and they are rated up to 600hp in a v-8 so 300hp in a four cyl, and I'll be under 200hp, so should be good. Pistons I plan on using are Icon IC723 designed for a ford, but the numbers work for my application. Using the flash driven calculator on the Eagle home page, the rod and piston combo will give me a 8.4:1 compression ratio, assuming a .04" head gasket thickness, and 45.6cc head volume. I plan on working the combustion chambers and opening them up, if I can open them up to 47cc that will knock me down to 8.3:1 and if the head gasket is .05 that will drop me down to 8.12:1 and that is a good turbo compression. Since I don't plan on running over 7psi.

If anyone is interested, the specs I used are:
deck height    9.125
bore                4.03
stroke             3.00
rod length      6.25
chamber vol  45.6            47
gasket thick  .04             .05
piston dome  -28.5 ( don't for get the minus sign!)
pin height      1.365

Still Unsure Which Engine To Build....

So I'm back in the internal debate of which engine to use, the 4cyl that came in the car or a 3400 v6. I guess I'll try the old pro and con list.

                 2.5  4cyl                                                             3400 v6  
         pro                           con                                pro                             con
1)already have       lower performance     |   higher performance      need to buy 

And that's as far as I get, with either engine I will have to purchase a new ecm and re-wire the engine (less wiring with the four cyl then the 6 cyl) and buy a prom emulator and reprogram the ecm. I will need to buy a new and bigger fuel pump. On the four cyl I will need to custom build an intake manifold and fuel system, but only will need four injectors, with the 6 cyl I will need six injectors and custom fuel system. With the four cyl I will need to make a turbo header, with the 6 cyl I will need to do even more exhaust work. I have a T25 turbo for the four cyl that just needs a rebuild kit, I will need to buy a different turbo for the 6 cyl(so far I can't figure out which turbo). The four cyl will need new rods and pistons and hi-po cam, the 6 cyl can use the factory internals, hi-po stuff is even pricier than the four cyl stuff. With the 6 cyl I will need a new flywheel, and need to fabricate a front mount. The four cyl will be unique, very few four cyl have a turbo if any, they are out there, but very few. The 6 cyl is more common and has more support in the aftermarket, look up http://www.wot-tech.com/shop/ they do a lot of 6 cyl stuff.

The other thing I have been considering is the way I drive, or will drive. I think the four cyl will survive just fine with my driving, I'm not trying to build a race car (road race or drag). I know the four cyl can't be revved past 5000 if I expect it to live, so I want to design the turbo system to spool up early. My basic goal is to be able to merge into highway traffic easily. The Fiero already handles great, I just need a little power boost. I know the 6 cyl will be more reliable and faster.

So this didn't help me decide either.