efturbo

hello all
iam currently fitting a to4 turbo to my EF 6cyl,(5 psi max)
i have got ba turbo injectors and i will be fitting a inline pump, xr6 fuel reg,water injection,but my question is which sensor controls the ignition timing? (crank angle or cam angle) i cannot afford a piggyback computer to control timing so thought of making a small system to retard the timing on boost , being a fitter and turner i thought of using a distributor vacume advance retard and mount the sensor on a swivel plate so when the 3 psi pressure switch is activated a 12v air switch will allow boost pressure to retard timing 10degrees to stop detonation , i know iam mad but i must be able to control timing when on boost somehow?without forking out big bucks , time costs me bugger all

thanks for any input

lee