Dynamic fuel computer instead of ECU?
If ECU has nothing to do with A/F ratio, I'm sorry. But the question about using a fuel computer stil remains.
Renntech and GIAC are testing chips now. Haven't heard either are being sold yet. There's a company in Australia that has a chip out but haven't heard much on that. Also Opera Design advertises a chip (http://www.opera-design.de).
My guess is that most chips on non-turbo cars like ours will get you about 6-8HP across the power band. A really good chip may double that. You'll read very high claims like 20-30hp but the dyno's I've seen show momentary spikes and aren't representative of what you will get.
Off course nothing compares to a pulley for biggest gain for the least bucks, specialy the ASP for $350. But if you already have a pulley then the chip is your next best gain.


