Variable fuel pressure

[blitzracing]

Anyone messed about with the fuel pressure ? Ive tried a "rising rate" type of fuel pressure regulator, but all that did was make the fuel consumption worse. I think the ECU already enrichens the mixture fast enough under acceleration, and this type of regulator just over fuels it. I assume that as all the regulator does is hold the fuel pressure at a fixed PSI above the inlet vaccume, then "one size fits all" can apply for any EFI setup. Looking at these ebay units:

http://cgi.ebay.co.uk/SUBARU-IMPREZA-WRX-FUEL-PRES...

Half the price of the RPI and the like offerings.Any comments please ?


Mark

[bhpjon]

blitzracing said:

Anyone messed about with the fuel pressure ? Ive tried a "rising rate" type of fuel pressure regulator, but all that did was make the fuel consumption worse. I think the ECU already enrichens the mixture fast enough under acceleration, and this type of regulator just over fuels it. I assume that as all the regulator does is hold the fuel pressure at a fixed PSI above the inlet vaccume, then "one size fits all" can apply for any EFI setup. Looking at these ebay units:

http://cgi.ebay.co.uk/SUBARU-IMPREZA-WRX-FUEL-PRES...

Half the price of the RPI and the like offerings.Any comments please ?


Mark

There is a bit about this in the bible because i was looking at this option a month ago, but it recommends against it for some reason (i can't remember unfortunately)

[rev-erend]

OK - I think I can explain.

The fuel pressure regulator also has an air pipe to the inlet manifold.

When the throttle is full open - there is very little pressure and the fuel regulator gives the full fuel pressure - normal setting is 43psi.

Between full throttle and closed the manifold pressure becomes higher - the fuel regulator sees this and drops the pressure - on mine as low as 33 psi - so in this way giving the pump an easier time.

THis is essentially doing the same job as a MAP (manifold pressure) sensor does - it's an engine load sensor.

Rev in one the spot - no load..

drive it and rev it high going up a hill - well thats a high load needing more fuel.

So - the pressure of the regulator can be changed and this will allow your injectors to flow more fuel than they would be able to at the moment ..

BUT

the entire system would need to be remapped.

In short - you are not gaining anything .. unless your engine is at the 'duration' limit of the injectors.

[spend]

Surely, if you just don't connect the vacuum line, you just have an adjustable pressure relief valve? & it has a gauge to boot

Dave

[blitzracing]

It think you are making things over complex. The fuel pressure requlator simply compensates for the variable amount of vacume in the inlet chamber the the prssure between the fuel rail and injector tip always remains the same. 37 -40 psi or so. Think about it other wise a large vacume in the inlet manifold (Throttle shut) would suck more fuel through the injector if the fuel rail

[blitzracing]

It think you are making things over complex. The fuel pressure requlator simply compensates for the variable amount of vacume in the inlet manifold so the pressure between the fuel rail and injector tip always remains the same. 37 -40 psi or so. Think about it other wise a large vacume in the inlet manifold (Throttle shut) would suck more fuel through the injector if the fuel rail just when you dont need it. All fuel enrichment is controled by the ECU and injector timing only. Thats why the units are "universal"

[GreenV8S]

Yes I agree. The point of the 'rising rate' regulators is to over-compensate for this pressure change, so there is more pressure across the injector under load and less off load. In principle this could be used to extend the range of the injector if you have trouble getting a short enough pulse at idle or they are saturating under load. For that to work you would want to have the map set up to achieve the correct fuelling to match though. Otherwise all you're really doing is richening up the engine under load. If the engine has been mapped to suit an ordinary (1:1) regulator then this means you're throwing excess fuel in which is likely to do more harm than good.

[clive f]

I have an fse adjustable regulator fitted on my griff after the standard one wore out, this was set up by Colin at Dulfords last week, he disconnected the vacumn pipe and set to 40psi at approx 1000rpm, runs fine no problems at all.

[Meatball]

clive f said:

I have an fse adjustable regulator fitted on my griff after the standard one wore out, this was set up by Colin at Dulfords last week, he disconnected the vacumn pipe and set to 40psi at approx 1000rpm, runs fine no problems at all.

Exactly the same here, Colin did mine about a month ago