Your car will still need setting up if its running 20Psi on ke-jet.
A fuel modification will be needed to supply the extra fuel required for the extra air your engine is consuming.
this can be done with the standrd ke-jet fueling and all that is required (as far as i understand it anyhow ) is a pressure increase.
the problem is that the ke-jet will overfuel on idle and mid throttle but will be fine on WOT.. this isnt a problem TBH as it will cool the bores etc.
The only thing is it will sting your wallet as it will gobble fuel hence why most people will go for a 5th injector after 20 odd Psi as it is MUCH more economical than running modified ke-jet only.