I added my input to the list below. Opinions will vary, so hopefully others will give some more input, but you will see some recurring themes here. The mods should be good for about 300bhp. Turbocharging is a nice, quieter way to make more hp and torque.

If you want a trick driveshaft, Mazdatrix sells an aluminum TII driveshaft for less than the price of a new OEM driveshaft.
http://www.mazdatrix.com/g9.htm

LOL, this forum is known for being blunt.

Thanks for the build info. I'll look into it.

Keep in mind these cars weigh well under 3000 pounds. So 200HP is nothing to sneeze at. There fun to drive and handle really well.
If you insist on making more than 200 HP, and keeping it streetable, your only option is forced induction.
If you turbo your motor and source parts correctly (find a tired TII), you will spend thousands less than building a 250 HP n/a motor.

There is a guy on here that built a cosmo motor with S5 rotors and a standalone making about 250. I can't remember his handle now, but you can find his threads in the n/a section. he builds motors in main or new york or something. he said if I sourced the block he could build one for about $2500. Not bad considering a PP will run way over that. That still requires a standalone.

A stock TII turbo will easily make 250. 350 is doable with a turbo upgrade and a tad more $$.

I've decided already that I'm going to do an S4 Turbo II swap.

Like Evil Aviator, I recommend BNR. I had my turbo built by them. Amazing job, amazing service, great power, low cost...

dude, get an s5 swap. better engine, better turbo.

This is my first build, I don't wanna get too complicated with it and don't wanna spend too much money. My second build will be much more extensive and cost more. I plan on using the S4 Turboo II motor and tranny and using the S5 Turbo and porting the waste gate. But I'm still open to suggestions.

I'm buying my FC on Saturday from my friend and I'm going to buy a shell to use for the build later on.

the s5 has stronger irons, and a better intake manifold, and better inter cooler.

The S4 BNR upgrade negates the S5 turbo advantage, S4 vs. S5 intercooler plumbing size is a moot point if a front mount intercooler is used, the stronger irons don't make any difference for an engine of 400bhp or less, and the intake manifold is not any better with respect to the turbo engines. I don't see how it is worth the trouble to swap a S5 turbo engine into a S4 car.

You can see from RETed's website guide that the S4 and S5 engines are basically even in the 250-400bhp range.
http://fc3spro.com/TECH/FM2W/power.htm

I'm gonna use an Isuzu FMIC that won't block as much airflow from the front dam, and I'm only looking to push 300-350rwhp for my first build. My second build will be a 20B Cosmo swap.

ok the commerical for the gxl s4 says 148 hp stock. add10-12 hp for s5 uim and lim, say another 10 for headers and full exhuast, and another 5 with a proper cone filter or KnN replacement filter. thats already 175 hp. and a streetport has to be good for over 25 hp at least i would hope so. so theres 200, plus theres 5 more for removing ps, and a few from throttle body mod, may not be at the wheels but its cheaper than alot of options.

don't forget -40hp for worn out housings and seals.

Ricer math. Those estimates are very optimistic.

i have a brand new crate 13b with only 10k on it, its not too tired.

you're warm. i think 10-12 is about right for the S5 intake, removing the cats is good for 5-10hp, header 0 (ive seen the header actually dyno less than the manifold, although the header engine was TIRED). cone filter does nothing.

so that's 165/175 which is about what we actually see. if you wanted more, you can contact gtorx7. and he can make you a really nice header/exhaust.

the street port might do 25, but its limited by the stock intake manifold.

It already has no power steering, and I've got the exhaust manifold with no exhaust so it's unrestricted.

what do you mean "no exhaust"?

probably means no piping after the manifold, or no mufflers and just straight pipe....holy deafening ears.
Thats pretty much bad for any power in low to mid range on a N/a

You are exactly right, I can get the catback for free from a guy in Phoenix but I still need the section between the manifold and the Y-pipe. If anyone is selling this or doesn't want it I would greatly appreciate it.

you are not going to get 200 wheel hp without tuning the intake (ie cutting it up) and you also need to have a fully custom exhaust. simply bolting stuff to the car will only net about 20 wheel hp.

lets not forget some way to tune the fuel and spark.

That's what the Rtek is for.

The Rtek has a downside to reach 400hp, the MAF.
The Rtek is good for under 400hp, I havent seen anybody go over it with one yet.
That and the injector sizing. Some people ran 1000cc with it and it does well.

i my self wasnt talking rwhp but brake hp. rear wheel is different and depends how well u can transfer the bhp to the rwhp. so im not too of as far as bhp goes but rwhp im way off.

no one talks about flywheel hp. real numbers are what you put to the ground.

thats why i chimed in to let you know i was wrong..