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Some excellent observations, Barry.
Regarding the workings at altitude - there would
certainly be a different fuel flow required at WOT at 4000 vs WOT at 12000
assuming NA engine. A manifold referenced fuel pressure regulator should
maintain a constant pressure differential between the pressure in the fuel rail
and that in the manifold therefore insuring that the same amount of fuel in
injected for the same injector-on time duration (pulse). So as you
increased altitude(and decreased manifold pressure at WOT) I would expect to see
the fuel pressure drop correspondingly to maintain the
differential. Or if turbocharged, I would expect to see the fuel
pressure increase as the boost goes up.
My fuel map has always been a bit rich at the lower
rpm range (idle), so it could be that when manifold pressure is low (such as at
idle) that the pressure differential is much larger meaning more fuel flows
per millisecond of injector on time than at higher manifold
pressure.
A different make of pressure regulator is
likely the only way I will know for certain.
Ed A
----- Original Message -----
Sent: Sunday, January 23, 2005 6:31
AM
Subject: [FlyRotary] Re: Ah Ha! Pressure
Regulator Problem?
Ed,
If you look around at other regulator brands, you'll
find you've got your "adjustable" (meaning that you set the pressure) and your
"adjustable rising rate" regulators. Rotary Performance sells the SX brand
adjustable regulator, which they claim will flow as much fuel as your pump can
throw at it (http://rx7.com/store/rx7/fcfuel.html).
Brian Cain, a rotary racer based outside Dallas who posts on that other list
occasionally, uses a Malpassi adjustable rising rate regulator. I did a quick
internet search but did not turn up any Malpassi vendors outside Australia
However, the latter regulator is really intended for turbo applications, where
the rising rate regulator is intended as a kind of kludge fix to get the
injectors to flow more at the top end. One warning I read was that you have to
start your fuel maps all over again if your fuel pressure increases, leading
to a richer fuel flow depending on manifold pressure.
One thought I
had was that you might be needlessly introducing a complicating variable if
you threw on an adjustable rising rate regulator. Wouldn't there be a
difference in the fuel pressure you got from your regulator if you were at WOT
at 4000' vs WOT at 12,000'? Your manifold pressure would be lower at the
higher elevation (without a turbo), leading your regulator to flow less.
I haven't worked out any math on this but on initial reflection it might be a
problem in an airplane that auto racers don't face (unless they're in the
Pike's Peak hill climb).
Barry Gardner
Wheaton, IL
Ed
Anderson wrote:
I think I may have found my problem with the
pressure regulator. Seen below (the Boost Adjustable one is the one I
use). In the description they mention are adjustable from 36-45 psi
with a flow rate of 9.2-10.5 gal/hr. I presume that means the
return rate flow or if they mean the engine fuel used flow rate then
clearly it is under-capacity to handle our rotary fuel
flow.
The Pump I use (see below) is rated
at 45 gal/hr at 40 psi. My nominal fuel flow at cruise is 7-8
gph. If my logic is correct that would mean the pressure regulator
would need to dump the unused flow of 45-8 = 37 gal/hour. Yet, it
seems that the regulator unit will only flow a max of 10.5 gal/hr. Is
a return of 10.5 gal/hr sufficient to keep the pressure at 40 psi while
using 8 gal/hr?? In fact, would that return rate be sufficient to
respond to manifold pressure variations? I would not think so -
but would like to hear what others may have as an opinion or knowledge on
the topic.
Thanks
Ed
Fuel Pressure Regulators
Maintaining
accurate fuel system pressure on any multiport EFI system is crucial to
performance. MSD’s Adjustable Fuel Pressure Regulators allow you to fine
tune the fuel pressure to meet the demands of your engine and injection
system. Both Regulators are adjustable from 36-45 psi with a flow rate of
9.2-10.5 gal/hr. The inlet and outlets are 5/16” and a jam nut is supplied
for special threads on the bottom to ease mounting to a bracket. These
rugged Regulators are free standing so they don’t have to be mounted
directly to a fuel rail and can be installed in any position. Fuel pressure
is set with an adjusting bolt and is locked in position with a locking
nut.
PN MSD2220
Boost
Adjustable
This Regulator is designed for turbo or supercharged engines.
As boost pressure increases, more fuel is required by the engine. This
regulator features a boost reference circuit that adds more fuel in relation
to boost pressure.
Boost/Fuel Pressure Regulator
PN MSD2222
High Pressure Electric Fuel
Pump
 Multiport EFI systems require a stable fuel
supply to maintain best performance throughout the engine’s rpm range. This
high pressure and high flow Fuel Pump features a roller vane pump mechanism
which is extremely resistant to clogging and jamming. The pump mounts
in-line (out of the fuel tank) with two supplied cushioned clamps for a
quick and sturdy installation. The nipple inlet is 3/8” with a 5/16” outlet.
The wire terminals feature brass studs for secure connections. Made in the
USA, the pump is ideal for use as a “booster” for nitrous oxide
applications, or as a stand alone pump for multiport EFI systems on engines
up to approximately 500 HP. Capable of 43 gph at 40 psi/162l/h.
PN
MSD2225
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