Mallory Ignition ACCEL CHEVROLET APPLICATIONS (including LT-1) 74022 - Manual (Page 6)

ACCEL/DFI ACCEL/DFI
ACCEL strongly urges the use of a good quality suppression
wire such as ACCEL 300+ or ACCEL RFI Suppression Wires.
We have encountered problems with various ignition wires
available on the market such as helically wound or solid core
not suppressing electrical noise. The use of these wires may
interfere with the operation of the ECM. Further, some high
energy aftermarket ignition units also produce electrical
fields which will interfere with the ECM’s operation. Use of
these units is strictly at the risk of the owner. Call ACCEL for
recommendations of ignition system compatibility.
The total advance you set the engine to will depend upon the
engine you have. Vacuum advance should be controlled with
the EGR port, which is located on the bottom of the throttle
body. ACCEL/DFI recommends a distributor with
adjustable vacuum advance. Once the total advance is set,
connect the vacuum advance canister. Adjust the vacuum
advance canister to maintain 20-26 degrees with a hot engine
at 800 RPM. Again, this is ACCEL’s recommendation,
depending upon the compression ratio and cam profile, you
may have to decrease timing to avoid detonation.
COMPUTER CONTROLLED IGNITION
If you are using a GM (F or Y body) computer controlled HEI
distributor the MWH’s four pin male black connector must
be used. When using a Y body HEI , the four pin between the
HEI and the MWH is compatible. However, if you are using
a F body HEI, the four pin connection on the MWH will not
plug directly into the distributor. In order to use a F body
HEI you will need additional wiring. ACCEL/DFI’s part
number 74170 will allow you to connect your distributor to
the MWH. You can also control timing with the ECM by
using a magnetic pick-up distributor or crank trigger. In
order to control timing with these ignition systems you
must get a modification done to your ECM (ACCEL/DFI
part number 74043-I), this modification will come with the
necessary additional wiring, but will not come with an
ignition enhancer box that is required. If you will need this
modification contact ACCEL/DFI for further instructions
and a shipping address.
In order to set the initial timing, the ignition bypass
connectors (white-one pin connector), incorporated into the
HEI leg of the main wiring harness, must be disconnected.
With the engine running hot at 800 RPM, manually adjust the
distributor to 6 degrees BTDC. Once adjusted, reconnect the
ignition bypass line. As soon as you connect the bypass line
the timing will then be controlled by the ECM. The spark
curve is preprogrammed into the ECM from ACCEL/DFI. It
has as initial timing of 20 degrees BTDC and a total timing of
34 degrees BTDC in by 3000 RPM. The timing curves, as well
as all other tables in the ECM, can be adjusted to better suit
your engines requirements using ACCEL/DFI’s calibration
software CALMAP.
NOTE: If an aftermarket ignition enhancer box
is used (i.e.: ACCEL 300+, MALLORY Hyfire)
the Y body HEI can be wired as described by
the manufacturer. However, if you are using
an F body HEI or controlling timing with a
magnetic pick-up distributor or crank trigger
please reference figures E and F.
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