ajustable fuel pressure regulator
Playing with the regulator will change fueling at all points, tuning in the pcm changes it only where it needs to be changed if done right.
By changing it at all points you affect part throtttle where the O2s help the pcm learn, if you use the regulator to lean it out then the pcm will learn and correct at part throttle and will add at WOT as well.
The stock tune is too rich as is so usually guys make the mistake of trying to correct that by turning down pressure which results in the temporary power gain CRAZZ28 talked about.
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As said they can be used to manipulate injector size if you have the wrong sized ibjectors.
, otherwise it serves no performance enhancing purpose for me! 





