>1.Terry suggests that the pump be mounted low for it to work less, but
wouldnt it >be the same amount of work, since it will have to pump it right
back up to carb >level ? (less vacum but more pressure)
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Pumps don't work as well siphoning, ESPECIALLY when dry so a gravity fed
system is easier on the pump itself. They are really designed to
pressurize or pump (liquid) fuel, not suck it up from the tank. The only
reason that the engine mounted pump is in the front far away from the fuel
source is because, obviously, that's the only place the engine can operate
it, not because it's better for the pump to operate there. If it were in
fact more advantages to mount the pump nearer the carburetor and farther
away from the tank, then new vehicle manufacturers using electric fuel
pumps, having been freed from the design constraints of an engine driven
pump, would most certainly have done so.
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>2.If there is an advantage to locating it lower why would the tank design
make a >difference? on the bottom feed it would obviously hold true, and on
the top feed >syphooning would take place making it irrelevant.
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Yes and no. If the tank has a top feed, then you do end up siphoning, but
you still have less line than if you mounted it near the carb - and as I
stated before, pumps were designed to push, rather than pull the fuel, plus
it STILL has the advantage of eliminating vapor lock, which mounting of the
pump closer to the carb would not.
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>3.Joe you suggest mounting the pump in the trunk for safety reasons, but
doesn´t that leave a lot more of your high pressure. line exposed to the
elements (under the car) as well as the under the hood?
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It does leave the line "exposed" as you mention, but unless you have port
fuel injection, you are talking about 3-4 psig for import cars, about 6-8
psig for American iron, and about 9-15 psig for even a throttle bodied fuel
injection system. If you couple the pump with an emergency fuel cutoff,
such as tying it into the oil pressure line, or checking for timing pulses
then the risk of spewing fuel when the engine is not running is minimized
if not eliminated.
Another advantage of running an electric fuel pump is that the carbs will
always have full float bowls upon startup especially after an extended
rest, something an engine driven pump won't be able to do.
Barry Schwartz (San Diego) bschwart@pacbell.net
72 PI, V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
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