The purpose of the latency is to make up for lost time. The way the distributor
operates causes a delay between when the reluctor passes the pole piece and the
signal reaches the ECM. This delay changes according to the RPM of the
distributor.
The code works by subtracting the latency value from the
spark advance value. However, at this point in the code the SA has already been
converted from an angle to time. Instead of 30 deg BTDC, it will be in
micro-seconds BTDC (In actuality it is usec's ATDC as it will be firing the next
cylinder is sequence. And because of that a subtraction of the latency value has
the SA event occuring sooner, making up for lost time).
Now, if my math
skills are still OK, here are some calc's that show by how much they adjust the
timing. Plug firing or 90 deg crank rotation intervals:
8 cylinders at
1600 RPM:
(1600 rpm) / (60 SecPerMin) = 26.67 Hz
(RPSeconds)
26.67 * (4 CylPerRev) = 106.67 plug firings per
second
1 / 106.67 = 0.009375, or 9.375 msec between plug
firings
9.375 / 90 deg of crank throw = 0.104167 msec per degree, or
104.167 usec
8 cylinders at 6400 RPM:
2.34375 msec between
plug firings
2.34375 / 90 deg of crank throw = .02604 msec per degree, or
26.04 usec
From AXKT the lastest '88 - '92 TBI
Firebird/Camaro BIN the SA latency at 1600 RPM is 305.2 usec's (This is a small
cap distributor).
At 104 usec per degree of crank rotation this is a
little under 3 degrees of timing.
Oddly enough the latency value in
AXKT at 4800 RPM is also 305.2 usec (there are different values at other RPMs).
That value will be used from 4800 RPM through max RPM.
With that at 6400
RPM wiath a latency of 305.2 usec is 11.7 degrees of SA
(substantial).
RBob.
Bookmarks