and
BigG, I have an NA and l think after the celica you'l appreciate the power increase even though its only around 220bhp. tbh, the most extra ponies you can get out of an NA is upto about 240ish, a conversion to single (i'm looking to do that, as are a few others here ) would cost around £2.5K for a kit if you want to DIY, or around £4K if you want someone like Turbofit to do it. it can get you an increase to around 300bhp or 400ish bhp, depending on the kit and £ you put into it.
Can I suggest you get some supra owners locally to take you out and give you an idea of performance? Twin turbo's - standard or BPU - are different to single tubbies but a lot depends on your budget.
There are some excellent guides on the forum, on the home page. Have a look to get a feel and sort out a ride or two. They're a great bunch here, I'm sure some of 'em will be happy to take you out.
Good luck!
lolx
Linda