The gtech isn't going to tell you anything about how your motor is running. It's an accelerometer. It measures acceleration.

A much more useful tuning tool in lieu of a dyno is a wide band oxygen sensor used in conjunction with some way of tuning your computer; be it a V-AFC, Hondata, AEM PEMS, whatever. Here's a nice relatively cheap one: http://www.techedge.com.au/vehicle/wbo2/default.htm

It gives pretty spot-on accurate readings of what your a/f ratio is and then you can use whatever mechanism to adjust the fuel curve to compensate.