It does what it says on the tin, it advances the ignition, fools the cars lpg ecu into thinking all is well and normal, but you can preset the advance amount over an dabove that normally offered by the lpg ecu/car ecu.
I ran a total of 58 degrees on my xr4i, the difference was night and day, in smoothness and power, suprisingly economy only bettered very slightly, but power was up big time.
On the rollers it made an extra 28lb ft at 1200rpm lower, but 22bhp extra at same rpm.
I used a WOLF 3N box of tricks, adjustable in 4 degree increments, you adjust it/advancing until it does not get any better then stop.
tabetha