More spark and fuel map tuning with reindexed cams

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From: doctorduke_REMOVE_756997_THIS_@yahoo.com

After passing my emission test I've done some more tuning in
non-emission configuration to optmize driveabililty.

To eliminate some idle speed inconsistency I added a second set of
light springs to keep the centrifugal advance from deploying until
1000 RPM - 100 higher than my 900 idle speed. I believe the idle
speed inconsistency was caused by having a small a but varying amount
of centrifugal advance at idle. Consistent and stable idle
characteristics require a fixed amount ignition timing. Any variation
in ignition timing can lead to inconsistent idle speed. Once fully
warmed up you'd almost think it has an automatic idle stabilization
system as on a modern car due to the very consistent idle speed.

My total WOT timing (initial plus centrifugal) is set at 32 degrees
and it's all in by about 2200. This yields about 13 degrees of
initial and the Delco D-1356 vacuum can adds 11 more for a total of 24
degees of idle timing, which is in the mid twenties ballpark that the
engine wants.

As far as fuel is concerning I am looking for the leanest acceptable
mixture in the idle/off idle/cruise range that will not result in any
driveability problems - hesistation, surging, etc. After trying
several different combinations of MAP sensor and idle pot settings, I
was back to having the MAP sensor at the OEM position with the idle
pot full rich - at the "R" limit of travel. This proved to be fine
except for a slight transient hesitation coming off idle. Since I had
not adjusted the throttle sensor position I knew that there was more
throttle travel before the idle position signal went to "off" due to
the lower idle throttle opening required by the reindexed cams.

After adjusting the throttle position switch IAW the shop manual the
hesitation went away about 95 percent, so I will probably readjust it
using an .008" feeler gage rather than the specified .016".

It's tough to attach test leads to the throttle position switch, so
since the ECU was laying on the toe board to facilitate access to the
idle pot I disconnected the harness and attached my test leads to the
harness pins. You can locate the proper pins from the shop manual
schematic, and be sure to pick the correct ground.

The good news here is that the fuel flow can be tuned without having
to deal with the MAP sensor, which eliminates another variable from
the equation.

Bear in mind that all my tuning work is being done with the D-1356
vacuum advance, so if you don't have one you're on your own. The
vacuum advance is necessary to generate enough total idle timing for
the engine to operate at peak efficiency and minimize heat generation,
which can lead to overheating.

During my emission test, which was on a 75 degree day, all the idling
caused the engine to heat up and the gauge was just short of 210
because I had set the initial at 8 and, of course, the vacuum advance
was disabled. This is required to pass emissions.

With the current setup the engine could idle indefinitely with the
temp gage never going above the hash mark between 100 and 210. (I
have the original 195 degree thermostat.) There is very little heat
coming out of the engine compartment, and, as before, you can almost
touch the header, since it's only running about 500 degrees.

Duke






[This is message #10622 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]