Some performance upgade questions

[twitchy]

Well here goes

I have a few questions for the experts out here, I just got a new job and will make gazillions of dollars this summer and need to ask about things to waste my money on souping up my already hot car.

First off:
-Is there a fuel computer that will help me to SAVE gas mileage (i shouldnt worry about it since i can afford it but I do...)
Something that I can adjust the ignition and fuel with to have like an economy, stock and sport mode kind of thing?

-I know this has been covered before, but what does the sr20det give you, like 200 horses? With the same amount of money what can you do to the KA24DE and why do lots of people seem to prefer the SR powerplant?

-how much can you add to the engine, power wise before you start to worry about compensating, like a better rad or strengthening the frame?

Can someone convince me that the car is fine the way it is and that I dont need to fix it up?? Cause when i bought it I swore I wouldnt do anything to it, but lately ive been tempted...