Paul-
I want to revisit the question of fuel line ID from the tank to the fuel
pumps. In the past, you have asserted that standard 1/4" ID lines are
not sufficient -- they do not flow enough fuel. Yet, looking at the
fuel pumps we have, and which were used on the dyno, I see that they are
1/4" ID themselves!
I ask, because it seems odd to plumb the tank-pump side differently than
the pump-injector side.
Also -- I am questioning whether there should be a gascolator in the
system. I believe you've stated in the past that the pumps, since they
are running all the time & returning fuel to the tank, will quickly mix
up the fuel & any water in the system such that the engine will be able
to run even though some water droplets are suspended in the fuel. (You
might want to add some of this design to the book too -- there is
nothing on the web site about this sort of thing)
Mark & Mark
We did not use those MSD pumps on the dyno. We used what ever
high pressure pumps Dave Lemon at Mazdatrix had installed on the
dyno. We did run it with 1/4 inch line but we never got over 250 HP.
People say 1/4" ID plumbing is enough and unfortunately some of the pumps
are 1/4" ID output. I would be more comfortable with 3/8" ID plumbing for
such an engine that might be capable of 300 HP. You don't want
it going lean at WOT or have the high pressure pump cavitate
because the lines are too small. Perhaps the inlet side is the
most important to have 3/8" ID.
Try 1/4" ID if it is easier and watch the mixture monitor, fuel pressure
and the EGT at high power. It might be OK.
I don't think I ever mentioned mixing the water and the fuel.
Seems to me the gascolator would have to be on the input side
of the high pressure pump. Fuel tank condensation is probably
the main source of water. I just don't know anything about this
situation with high pressure pumps and gascolators. They are not
used in EFI cars so maybe it is not a problem.
Gas line freezing was a big problem in the old days with carbs
so we used to carry a can of alcohol with us in the winter time.
In the wilds of Northern Ontario you could be driving down the road
at - 40 deg F and have the engine stop for no apparent reason.
You grab your can of alcohol, jump out, pour it in the tank
and by the time you got back in the car the engine would
start right up. Maybe the answer then is to mix a bit of
alcohol in the fuel. Apparently the alcohol is attracted
directly to the water in the fuel. What are you guys from
up north seeing in the winter time with EFI cars?
Paul Lamar
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