RE: Rising rate Fuel press. reg on forced indution BMW? **Rob

["Rob Levinson" <always_coca-cola@xxxxxxx>]

"Rob" (not me!)<motor@domain.elided> wrote:

>Subject: Rising rate Fuel press. reg on  forced indution BMW?
>
>    Is anyone using a "rising rate" fuel pressure regulator on their
>Supercharged or Turbocharged BMW's??   This is not to be confused with a
>fuel pressure "riser" or other add-on , but rather a fuel pressure
regualtor
>that increases fuel pressure at more than a 1:1 ratio based on manifold
>pressure.
> Any experience with these??   Any comments??  I've *heard* that these can
>be hard to tune?



        I've had one on Helen, my '85 535i Callaway Turbo.  It's that
generic mechanical kind like BavAuto sells.  Mine, I think probably
atypically for this kind of device, spends a lot of time in the shop being
repaired (bad diaphragm).

        It's rather crude, raising pressure in the fuel system by limiting
return pressure (pinching it off) and may cause injector life to be
shortened.

        My experience with it is that it does a damn good job.  From
Callaway, the car has a 7th injector in the intake tract (it looks exactly
like a cold-start injector) but I've never been pleased with its operation.
The Variable Fuel Pressure regulator (hereinafter referred to as VFP) gives
the car a little more feeling of "urgency", it wants to go like RIGHT NOW
rather than waiting for the turbo to spool up.  In really hot weather, the
car would have a problem with predetonation at extended high boost levels
(greater than 8lbs).  With the VFP, the boost can be dialed up to 12+ and
held there without any problem.

        Getting it calibrated was no big deal.  I attached a fuel pressure
guage in the fuel line and taped it to my windshield so I could see it while
driving.  I went out on the highway and stood on the gas until I heard the
first little pre-detonation zzt zzt zzt.  I would pull over, crank up the
adjuster on the VFP, and repeat the process.  With the pressure guage, I was
able to determine that 80psi was the correct peak pressure that I wanted
(that way I could re-calibrate the VFP later if necessary without having to
re-experiment).

        Normal cruising fuel mileage is completely unaffected because when
there's no boost, there's no increase in fuel pressure.

        As I said earlier, this is a crude way to get the desired result of
increased enrichment.  Better systems from Haltech/Electromotive will adjust
injector duration or control additional injectors.  But that's a little too
high-tech for a 13-year-old 300hp car.   ;-)

- - Rob Levinson
'85 535i Turbo - www.bubbaclub.com/rob/callaway.htm
'86 535i lowered suspension and snow tires... uh...

www.shortshifter.com

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