i dont know if the stated improvments actually occur in the performance of the car... but the basic premise works as follows...
DC voltage is actually the difference of the positive wire and the ground wire. (12volts DC positive wire - .3 volts DC ground wire = 11.7 volts DC)
what they claim is that they stabilize the ground voltage to as close to ZERO volts as possible and keeping the fluzuation of that ground voltage as steady as possible. this in turn will enables to sensors to work more efficiently. since the sensors make readings of temp., RPM, or amout of air and convert that number into a voltage or current. those voltages or currents are sent to the ECU and precessed to make decisions. the more stable the ground voltages are the better the readings will be when they are processed by the ECU.
i cannot attest to the engine improvments claimed by that ebay add... but i can say that many of the people i know who use this item find that the best impovment is found in audio sound quality. if you may, in a long stretch, it can be compared to the capacitor. if the voltage is not as close to 12 volts as possible when the bass hit comes, the correct amount of power and current cannot be supplied to the amp and subs. with a stable ground as close to zero volts as possible, the amplification circuit works as desired. the most noticible effect was with a digital radio tuner... cannot explain this but witnessed the improvment myself.
during my senior year in highschool, i did a project that involved 3 amps,3 farads capacitance, 5 10 inch subs and 15 inch sub running off one car battery with a 120amp alternator. when the bass hit, my idle rpm would drop from about 800-925 rpm to about 100-200 rpm's less. i never tested this, but i wonder if this could be related to how a faulty or "noisy" ground affects the car. when the bass hit and the current was drawn from the battery, the voltage seen by the car was ovbiously less than 12 volts (even with 3 farads capacitance) which may have been why the RPM would drop.
i DO believe that sufficient capacitance and a stabilized ground you WILL see an improvment in the quality of you idle and throttle repsonse and not to mention better sound quality.
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