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June 05, 2003
Actually, Jeremy...
The crankcase pressure is in and of itself
the propellent in a "ventilated" rather than
"evacuated" system, the former of which
I prefer for exactly the reason you state in
your post to Guy Weller....less dilution
of already diluted octanes.
Fr'instance, I think it was Chris who mentioned dragsters with vacuum
pumps
hooked up to evacuate crankcase pressure and considering THEIR
applications I can well nigh understand
this, considering THEIR crankcase pressures!! Whoa, whoa!! :)
Obviously, for the normal LBC daily
driver this would be overkill but the point
is made, though we are talking apples
and oranges in applications and "extremes" in crankcase pressures.
Our problem in a ventilated system is
"adequate" ventilation to allow the vapours/pressures to escape as they
are produced, most especially in light
of the stock "scroll" set-up which serves
as a rear main bearing oil seal.
In my 90+HP at the wheels Vizardized 1340cc powered '74 Spridget (scroll
seal)
I used two 1/2" vents and one
1" vent into a catch can. No oil leaks.
At 80k miles on this engine there was
some seepage in the scroll area but
pretty minor. This was a 7,000 rpm engine
BTW which saw 6,000rpm pretty often and cruised around 4,000rpm much of
the
time I was commuting down to NYC airports to my "office". A draught tube
was
plumbed into the catch can.
I did drive this car "like I stole it", regularly! :)
My current 1293 is a low/mid-range torque
producer hooked to a Datsun 5 speed using a 3.7 diff. It rarely sees
anything
over 5k. It gets by with one 1/2" vent off
the valve cover and a 1" vent off the old
mechanical fuel pump fitting. The rear
engine plate is the aluminum Rivergate
type with "real" rear mail bearing seal
incorporated in it's manufacture. No oil
leaks. It's not even using a catch can
yet. Just K&N filters on tubes with planned
vertical travel. The 1" takeoff from the
old mechanical fuel pump fitting keeps
liquid in the sump by it's vertical position,
and 1/2" hose off the valve cover is
travels in an "arc" so as to "trap" liquid.
I check it every oil change. So far, no
liquid to drain! Both vents are capped by
small K&N filters which exhaust in airflow
by the radiator and the pistons are equipped with Total Seal rings to
keep
combustion pressures more "up top".
This having been said.....
I see nothing wrong with the
normal PCV system which obviously has
it's good points as mentioned by both
Guy, Chris and others. It's inlet tract can
be "flushed" and kept clean of residue
build-up and the combustion chambers
can be kept clean as well with a spritz
of water injected through the carbs.
every now and then. I used to do this
once or twice a year on my PCV valve
equipped MGB. Not a matter of life and/or death any case. Sort of like
"induction"
spring cleaning!
Back in the days of my PCV equipped
MGB, we had 100+RON gasolines readily
available. A little oil in the combustion process didn't bother me at
the 10.0-1 compression ratio I was running. Just
cleaned everything out twice a year.
octane leaded gasolines. Today, we have
garbage octanes.....insofar as these older
engines are concerned.
And I see nothing wrong with bilge pump
exhaust fans being used to help the
"ventilated" rather than "evacuated"
system, either. If you've got the time and
the inclination....why not?! :)
The point is making an "educated choice"
should one be so inclined. That's why
I buy books by Daniel Stapleton and
David Vizard and read them...again and
again!! :)
Having an aviation background also helps
because I get to talk to a lot of our mechanics who know a great deal
more
about engines than I do. These guys are
definitely into their cars as well, especially
the younger guys who seem to prefer
US "muscle cars".
They see me coming and right away....
"Hey...here comes the dude with the toy
car". I tell them it produces about 100HP
and they about fall on the floor, laughing....very embarrassing!! :):)
Cap'n. Bob
'60 :{)
PilotRob@... 22371
Posted on June 5, 2003 08:08 AM
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