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Old 08-08-2006   #1
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Adjusting fuel pressure regulator

As many of you will already know an fse power boost valve is an adjustable fuel pressure regulator that allows you to adjust the rate at which fuel leaves the fuel rail (the release pressure) which effectively adjusts the pressure in the fuel rail, or at least reduces the rate at which pressure is lost during hard acceleration making more fuel enter per injection. in theory the extra fuel allows more power to be released.

the effects of this have never been tested on a car of my own but i've seen several RR printouts that suggest the effect is bad on a standard car. a friend of mine mentioned that he was going to buy one so I asked him to do some experiments during the set up. his only mods are an air filter and back box, so its basically a standard car. he had the RR setup in may and the results are interesting to say the least.

the standard fuel pressure regulator was tested and found to release at 3.05 bar, this produced approx 150bhp. the standard power boost vslve was set at 3.2bar and produced 148bhp, although both the power and torque curves were noticably smoother. with the power boost valve adjusted to 3.5bar the power dropped to 144bhp. those are the only results i have, but using them i've created a curve which shows the effect of the fuel pressure regulation value on power.

obviously i only have 3 results so i have to assume that below the stock valve of 3bar the effect on power will be the same as going above that value (i.e. stock value creates most power), i also assume the curve will be fairly smooth. if this curve is correct it would suggest that the stock fuel pressure regulator is already set at the best possible value for the car.

i've thought about this idea a lot lately, and i'm starting to wonder if my assumed curve would actually be correct. yesterday i was reading about fuel pressure regulators and found that the tolerance for then is +-0.2bar, meaning a stock regulator could be 2.8-3.2 bar for example. according to the tests done on the fse boost valve that tolerance could have a (relatively) big impact on the power and performance of the engine. with this informaiton in mind im planning on searching scrapyards for at least half a dozen regulators with different values, hopefully i'll be able to get a series with 2.8, 2.9, 3.0, 3.1 and 3.2 bar. from these i'll do tests to find out how accurate my assumed curve was. who knows maybe lower values will actually increase power output?

i plan to find out the best value for my car and use a stock fuel pressure rgulator of that value, rather than buying a fse power boost valve, which im very put off buying due to the results i've seen in the past. i'm wondering if anyone else has experimented with adjustment of the release pressure on their fuel pressure regulator, or experimented with the set up of a power boost valve. does the power drop below stock values? is the average of the stock tolerances (3bar) the best possible value to have?
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Last edited by jug; 08-08-2006 at 12:40.
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