Are you running the original L98? The only thing I would advise is changing to higher flow cylinder heads, intake manifold, less restritive exhaust systems with headers and possibly a cam swap.

Once your top and bottom end are "beefed up" you could either add a supercharger or a nitrous system.

Don't you already have a discussion topic regarding this?

add a twin turbo

do an engine swap

Build a stroker engine and change the heads and up the compression.

i say... while the engine is stripped, dont fuck around, spend some good cash at first, and you wont have many other problems, stroke it,bigger injectors, valves, pistons and twin turbo!!! fucken hey...holden/chevrolet... kings of the fucking mountain!

Make sure you beef up the bottom end first, better crank, rods, ARP main studs and rod bolts, good bearings like clevitte 77, have a machine shop bore it out, hone with a torque plate and balance it, then worry about your top end like heads, intake, cam etc.  

Only one way without tearing it apart and replacing a lot of parts.... NOS

if its the L98 you can gain majoy power from replacing the heads intake plenum and throttle body you should be making 350 + hp and 425lb torque

New top end, forged internals, supercharger.

PROCHARGER, SLP HEADERS, FLOWMASTER EXHAUST, COLD AIR INDUCTION, STROKE IT OUT, FUEL ADJUSTMENT.   It worked for me son.

Not if he wants 150-200 hp gain thats a large shot and would completely destroy a stock internal engine.

tubo or a supercarger....you could also do a 150 shot of nos....but not really for street use

The stock L98 is plenty strong for a 150 shot of NOS...  I should know....  my 87 IROC is just fine and is all stock!!

All things in moderation though,  I don't go around using it all the time.  

BBK has a new intake design to give l98 and lb9 motors a 60 hp increase with no other mods.....  add a larger TB recalibrate the ECM... Then heads, cam, exhaust shouldn't be too much of a problem to get 150 hp more out of the motor, but lots of parts.  Just rip out the motor and drop in a crate motor.  Run an edelbrock crate motor w/ a carb and get 420hp out of the box without the headaches

Wow, everyone's really into the superchargers and turbos. Just me personally, lovin the old school, I'd add a 6-71 blower with two 4bbl carbs but then you'd have to cut open the hood so everything could stick out. A new cam, set of heads, and headers would probably be necessary. That all said and done you're probably out about $4,500 if you do all the work yourself but would easily have your 200hp increase.

thats easy replace the top end assembly (cam, heads, manifold, and throttle body) then if you dont it your mark with that strap in a NOS tank (but like the guy said before those 350 are practicly bullet proof you could just go for the now if you wanted)

to bad it fuel injected no carb

I'd recommend putting ANOTHER L98 in the hatch ... lifting and adding another ale in the front. 4X4 IROC!!!!!!!!!!!!!

You can do the version of heads/cam but the TPI intake gives up power at 4750 rpm, so get a holley stealth ram intake, its 35 hp on a stock motor with exhaust manifolds.  So get the intake, then get some shorty or longtube headers and exhaust, lighten the car up, get rid of the parasitic losses on the motor like A/C, power steering and smog pump.  Check out my site at www.cardomain.com/ride/471099 and see what I've done with my formula, I do have a max ported stealthram, ready for my heads, but I want to try this intake on my firebird, it worked great on my iroc-z.  Before when my firebird was mostly stock, the best I ran with the L98 TPI 350 motor, I ran a 14.86 @ 93 mph, my iroc ran 13.81 at 99 mph, now with the work I've done to it, it is est about 354 horses.  But in my 87 iroc-z with the same drivetrain and everything, but weighed 3115  lbs, while my firebird weighed 3555 with me, I did the rear suspension, and made two runs right off the street with street tires, and ran 13.81's at 99, but the third run, the 3-4 clutch pak let go, so I drove home took the trans out, and next year I put a fresh one in.  But I only drove the car for about a week 1/2 with the fresh trans, and had a horrible accident, and the car was destroyed, but not because of me driving it, but a deer got in the way, and I tried to avoid it and it didn't work.

But check out what I did to mine, and maybe it will give you some ideas, its all posted for my iroc at www.cardomain.com/ride/471099/8 the firebird stuff is on the first page, but I also have videos of it running at www.myspace.com/cronsformula and I have other vid's too of my iroc before the accident.

I'd get rid of the fuel injection crap.... far too complicated for me. I understand the carbs better... but thats if I was doing the work myself, if I was going to let someone else work on my car all the time because I knew nothing about them, I might leave the fuel injection.