Dont know if any ones has done this but iv tried something that i did to my vectra gsi. The standard fuel regulator is set at 3.0 bar but if you fit a fuel regulator from a vectra 2.6 (Y26SE engine) its set at 3.8bar might not sound much but it works quite well, seems to boost lower and you get a nice burble on over run from exhaust. The part number is 9198822 and its alot cheaper (at about £13) than those power boost valve thingys that i dont particually trust. Its really easy to change just lift vehicle or get underneath, on drivers side above steering rack is the regulator undo to torx 25 bolt and gently pry from housing *carefull* as fuel may dribble down, pull off vacum hoseand rebuild in reverse order.. nice cheap mod it made a little difference (Every little bit helps) here's some pics.
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