An interesting development...playing in the garage
just now. Some of you might have noticed the plastic
bag next to my air cleaner covering the electrical connector
of the wideband 02 sensor in the exhaust pipe at Carlisle.
This is a 5 wire, heated, calibrated unit. Not the typical
on/off, 13-17a/f scale 1,2,3 wire sensor. This sensor
will read from 10 to 25 a/f in true lambda format. Circuitry
(lots of it) converts the signal to A/F scale, and is displayed
as a digital readout repeatably accurate to 0.2 A/F
Anyway.... Just before Carlisle I had set the ZS carb needles
with the wb02 reading. A nice steady 14.8 (14.7 is 'perfect' stoic)
Now the interesting part.....
With everyone talking about crankcase pressure and venting
I decided to experiment with my emissions setup. Currently...
as bone stock as it came as designed back in '73. (GT6)
Now the rocker cover vent pipe feeds into the carbon canister and T's
off and feed into two pipes directly into the throats of the twin ZS
carbs. The interesting part is the connection is BETWEEN the piston
and the butterfly valve. That is to say, the crank fumes go back into
the carbs to be burned, on the intake side of the piston and
metering needle.
So.... I thought....what is that doing to the A/F ratio... if pressurized
air is being forced into the carbs, AFTER the needles?
Sure enough! Pop off the hose from the valve cover, and the
revs rise. Well that's expected as it is now sucking air like a
vacuum leak. So I put my thumb over the pipe and the idle
drops right to where it should be (currently set to ~950rpm)
So I look over at the wb02 meter. Thumb on the pipe... idle A/F is now
at 15.8. LEAN! HHmmmm. plug the pipe back on the valve cover...
right back to, and dancing around 14.7-14.9 on the meter.
Again... I ponder...So at high revs...I must be forcing even MORE air
in past the carb piston so it must be running even leaner? hhhmmm
Since the intake is sucking air from a source OTHER than through
and under the piston/needle, I have to believe the piston position is NOT
correct for the breathing rate/requirements of the engine regardless
of needle position or taper as all the air is not passing over the bridge
of the carbs.
So here we go... I'm about to re-design the crank venting system.
to work as it 'should' .
To shorten the story a bit here....the plans are....
re-route the rocker cover vent to a catch tank, with a small diameter
pipette return tap, to allow any accumulated oil to drain back to the pan.
The top vent from the catch tank will be plumbed back to the air
filter side of the carbs to be re-inhaled. (GT6 air filter box 'bottom'
openings) The carbon canister will remain, as the fuel tank vent
and secondary breather vent for the top of the catch tank. My
anti run-on valve will still work that way as it will still apply vacuum
to the carb float bowls at shut down and still vent to atmosphere
as normal.
:-| ... documentation.... see the need for a new web page here.....
Paul Tegler
ptegler@cablespeed.com
www.teglerizer.com
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