I'd go turbo, but if you just want to tinker cheaply beyond the usual intake/headers/exhaust you can add a plate to the plenum (common modification in Japan NA's). Additionally, have a bit of fun with some giggle gas (50 dry shot).
 
15.3 is actually quite respectable for an NA 3SGE.

+1 to sorting out your suspension/chassis/brakes before you go chasing power out of a 3SGE.
 
What black93 is saying I think is true. It doesn't make sense to work an NA motor when there's a bolt in turbo replacement. Atleast in the $ - Kw department but if you love NA engines then fair enough.
 
just_ace's build list is spot on. But be prepared for it to cost a lot. I'd just get the panel filter and extractors, stop there, and then start saving for a V6/turbo swap.
 

buy a red-top Beams 3SGE from NZ.  Wire it in and then you win.

Then supercharge it and shout far and wide of how great it is.

MRVirgin

Then supercharge it and shout far and wide of how great it is.

GO SC!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Rotrex POWWAAAAAH!
 
I give it 6 hrs until he appears

hahaha maybe I should rob a bank then go twin charge my 3SGTE for ****s and giggles. :P

Bloody trolls...

On the money with 6 hours it seems

it's true buying a turbo should be cheaper and upgradeing your brakes,shocks,suspension makes the car handle so much better ,i did all the above to mine and also what i stated in my last msg .I like the n/a its cheap on fuel and sounds better then most turbo's mr2s ,plus all the upgrades i did on my 95 bathurst will keep up with a stock turbo mr2 i have race a few and i tell you what who says you cant make a n/a fast ? i have a mate that has an gt mr2 and loves to drive my car around i guess upgradeing your suspension and reconditioning your engine can make it feel better and smoother then most mr2s out there ... so i dont mind the n/a mr2 if you are after something crazy fast then why not a turbo ? thats what ill be doing as soon as i get bored ...