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December 05, 2003
Jim...
OK...you want to run "vented" instead
of "closed loop" but wish to retain the
charcoal cannister and use it as a
catch can either in it's present position
or possibly elsewhere in the engine
compartment.
Fine...but you MUST promise to read
the last paragraph! :)
I am strictly a layman in the post '67
emissions systems which were strapped
to our engines as "add on" devici,
providing for a "closed loop"
system to ensure crankcase/fuel tank
vapor evacuation into the combustion
process. Ripped it out myself, and never
used one. I took a look at it under the
hood when I first aquired my '74 Midget.
It made me vomit. I was immediately sick.
Being extremely bright and already having
a healthy distrust of government anything,
I immediately realized it ALL must go
in the interests of power/efficiency.
Back to basics and the KISS principal.
My MGA didn't need all this crap so obviously, the Midget didn't need it
either.
So it all went. All of it. The fuel tank got a
vented cap, and so did the crankcase via
the oil filler cap. A Maxwell House coffee
tin got painted a glorious gloss black and became a catch catch with
appropriate holes in appropriate places.
The graduated orifices had to go. The
orifice valve cover takeoff got snipped off
for a more "manly" 1/2" opening. The
orifice carb. emissions intakes got capped. timing case flame arrestor
hose
got "re-routed". Fuel "expansion tank" got
capped.
The carb. mixture adustment
"range restrictors" got cut. The air pump
got tossed (you know how heavy that
damn thing was? Geesh! And a drag on
horsepower to boot.......sacrilege!
I just want to make this clear. If anybody
knows differently from what I am about
to write, please join in and pipe up so
we can all benefit and learn.
The carbon cannister serves as an
"inbound" filtered air source. Part of that air is coming from the fuel
(tank) system
vapors exhausted into the charcoal
cannister through an expansion tank in
the trunk with lines up to the charcoal
cannister.
So that cannister is serving
as basically an "inbound filtered" air source to the crankcase whose
vapours
are exhausted into the combustion process via the hose from the timing
cover through (via the "T" fitting) "graduated" orifices in each carb.
Engine vacuum provides the motive
for flow and then there's that pesky
gulp valve "powered" by the air pump.
which provides for the required volume
of air under periods of "heavy" crankcase depression.
So I wouldn't even be thinking of using
the carbon cannister for "outbound" flow
considering the fuel tank hookup to begin
with, despite the fact the carbon cannister has an overboard vent,
unless one
"capped off" the fuel tank hook up to the
charcoal cannister (at which point you would need a vented cap for the
fuel tank
"breathing").
Now you would be free to use the carbon
cannister as a "catch can" as far as I
can see, assuming it will be free breathing
both ways. This would require
a nice large vent line from the cannister
to ground. I think this was a tiny line in
the stock hook-up but it's been so long
I'm not sure.
Now I do not like mixing vent ports with
each other on the way to the catch can.
I like individual lines. I wanna be sure
each vent line is feeding into a "free
area" instead of into each other before
they get to a common area from which
there is a LARGE vent line to outside
air providing for unobstructed two way
crankcase breathing.
It's not that I don't like the idea of the
valve cover vent having sex with the lower
crankcase vent(s) or all three having
sex together. True, it's "incestuous
venting" but we are living in the 2000's
after all. :)
You mentioned APT. When it comes to
sound advice in terms of APT, I think a
personal discussion with Dave Anton
(the boss) would be a good thing. He's
the man with the experience level, after
all. There may be something in joining
the vent lines prior to the reservoir
(catch can) which may be a bad idea.
Remember something. Part of the reason
for a Positive Crankcase Ventilation system was to insure against
crankcase explosion. So, positively sucking vapors out of the crankcase
wasn't solely an
emissions consideration.
Now I do not personally know of a case
of crankcase explosion. But I have heard
of the same though I do not know of the
circumstances under which this occurred.
But, methinks this should give one pause for at least consideration.
Cap'n. Bob
'60 :{)
PilotRob@... 27270
Posted on December 5, 2003 06:56 AM
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