Gernot Vonhoegen wrote:
>
> <,to replace the Lucas pump with a Bosch model (quite <common
> swap).>
>
> Sure COMMON BUT NOT WITHOUT ITS OWN PROBLEMS. best use the priming
> pump, say a low pressure solid state pump.
What are people in the TSSC saying about Bosch pumps which doesn't
filter over across the pond? The general assessment I've read is that
the Bosch unit is a superior pump. What are the problems associated with
that one?
> <It seems far more logical to keep the pump outside the car <where
> it's in
> <the airstream, and, if need be, provide some sort of heat sink <for
> the motor case.
>
> True, but that'll expose it to the elements and you need to make sure, that
> its well sealed, otherwise it will only run for about three years and then
> the electrics will play up as anyone playing with hot Minis will know.
> Nevertheless this is probably the best solution.
I won't argue about the environmental exposure--in lots of places in
this country and in Europe, that is a concern. However, I live in
southeastern New Mexico, and the elements don't show up that much around
here (~30 cm of rainfall/yr). When it does rain, I can't drive the GT6,
anyway--it usually floods around here, and that means water starts
coming in the door sills. (!)
> > <Further, if it's below the tank just enough, head pressure
> <in the tank will help feed the inlet. After all, vapor lock is
> <common
> <enough in hot climates with carbureted cars--and it almost <always
> occurs
> <on the inlet side of the pump, causing the pump to starve <and lose
> <prime. Same principle should apply with a high-pressure <electric
> pump.
> Too true, could even save you the priming pump.
One of the other things which can be done, which recently occurs to me,
is that the return line can be teed into the pump inlet line a ways
ahead of the pump inlet. Residual pressure in the return line is
probably higher than head pressure, anyway. This would also minimize the
problem of using a non-PI tank (the PI tank having, as I understand it,
a circular baffle built around the tank outlet, to prevent starvation on
turns when the tank level is low). The concerns with this method, of
course, are two-fold--turbulence interfering with inlet flow, and fuel
temperature at the inlet. I think both of those concerns could be
minimized with sensible design.
> <pressure, since it's entirely mechanical, and in such a <system,
> rate of
> <flow is affected by pressure. I'd have to see the innards of the
> <metering unit to be more positive about that, though.
>
> Another comment, I have read prices of reco metering units, which read a bit
> too low for my liking, make sure you look at the unleaded section of the
> reconditioned units, otherwise the thing just won't run lng enough to
> justify its price.
I wonder about this. This may be a function of the clearances and
materials in the Lucas pump, but a similar problem exists in diesel
injection pumps (and, of course, diesel fuel has never had lead, since
there is no need). About three years ago in the US, allowable sulfur
content in diesel fuel was reduced for emissions purposes. There were
shrieks of outrage from all the truckers that this would ruin their
injection pumps, but it didn't. Sulfur acts as lubricant, and since
there is a little in gasoline, it may be enough to keep the metering
unit okay. Allowable sulfur in unleaded fuel here is something like
0.3-0.5% by weight.
However, it does depend upon the construction of the Lucas metering
unit--they may well need leaded fuel, or need specific reconditioning
for unleaded fuel. For those people with PI systems who are worried
about metering unit life on unleaded, there are fuel additives for
high-pressure diesel injection pumps which may be of help.
> Next comment is that the cr of injection engines is higher than at least the
> one of late ec engines.
I'm told by at least one original PI owner in this country that
compression ratio is a factor in proper performance, and that the
metering curves are adjusted for an engine with approximately 9.5:1
compression ratio.
Cheers, Gernot.
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