The way I understand it, both sensors put out the same voltage range. In the 2-bar, 0-5v (or whatever the real range is) represents -15 to +15psi. In the 3-bar, 0-5v represents -15 to +30psi. Therefore, a 2-bar at 10psi and a 3-bar at 10psi will put out different voltages. You need to have a chip that's properly calibrated for the voltages that the MAP puts out... A stock chip would see a 3-bar's 30psi (maximum reading) as 15psi, and an Ultimate would see a 2-bar's 15psi (maximum reading also) as 30psi...